Rioja Wine Classification


last update: 22 January 2022

La Rioja Logo

Wine in general, and Rioja in particular, is bound by a series of very precise national and European regulations. In Spain the appellation of origin (denominación de origen or DO) is part of a regulatory geographical indication system used for all foodstuffs, including wines. Geographical indications and trademarks are distinctive signs used to convey information about the origin of goods or services, and consumers indirectly associate them with specific characteristics, qualities and reputations. Geographical indications tell consumers about the place of origin of products, and trademarks indicate the specific company that provides a particular product or service.

An appellation of origin is a kind of geographic indication, and it can be an actual place name, or a name associated with a place. The important feature is that it both defines a geographical origin and a quality or characteristic linked to that place of origin, e.g. Prosciutto di San Daniele is protected by European law (DOP or denominazione di origine protetta) and is an uncooked, unsmoked, and dry-cured ham from San Daniele del Friuli, which is different from Prosciutto di Parma (which has a separate DOP protection). Collectively consumers have the right to expect that producers respect very strict rules concerning the preparation of the foodstuffs such as hams, but in addition consumers expect San Daniele ham to be dry-salted with sea salt and aged for a minimum of 400 days, whereas for Parma ham the cotenna (rind) should be treated with wet salt, the lean part of the thigh with dry salt, and ageing must be for at least 12 months. Physically the two hams look different, with San Daniele being a flatter guitar shape because it's pressed during salting, whereas Parma ham is rounder in shape, and this difference should be seen in the shape of the slice. Parma ham is aged in a more humid atmosphere and should therefore be a bit softer, whereas San Daniele usually will appear slightly darker and have a more mature appearance. Another visible difference is that each ham has a distinctive hot-iron branding on the skin, but in addition a Parma ham has a shorter zampino (stem or foot).

In 2016 the Spanish "
denominación de origen" (DO) was registered as part of the European Union Protected Designations of Origin (denominación de origen protegrida or DOP), the EU-wide geographical indication which protects geographic origins and indication, as well as traditional specialities, for all types of agricultural products and foodstuffs (including wines). This is the system that protects San Daniele and Parma hams, as well as Camembert, Feta and Champagne.

Rioja's denominación de origen protegrida (DOP) is actually a subset of the European Union "Quality Wine Produced in Specified Regions" (QWPSR or QWpsr). The European Union has two quality categories, namely QWPSR and Table Wines, as well as a similar system for sparking wines. However EU Member States may have more than two levels of classification, provided they all respect the minimum standard set out in the EU wine regulations. Spain has taken up this option and introduced a higher level classification called denominación de origen calificada or DOCa.

So firstly, the Spanish
denominación de origen calificada (DOCa) is part of the European Protected Designation of Origin. Secondly, it is a "higher" quality standard that the Spanish denominación de origen protegrida (DOP). Thirdly, at present only two wines have been awarded this category, namely Rioja in 1991 and the Catalan wine Priorat in 2003. Lastly, what is explicitly required is that there must be a standards-based qualification process drawn up by a Regulatory Board (Consejo Regulador) to determine if a wine is eligible for Rioja protection, or not.

It's also worth noting that the rules for
Rioja wines were quite stable until a new set were introduced on January 1, 2019. Rules which included a number of important modifications. This webpage is focussed on the rules for red wines, whilst recognising that the Rioja wine region also produces white, rosé and sparkling wines.

Why was there a need for a new set of rules in 2019? It would appear that both consumers and winemakers were interested in seeing more information on the labels, and in particular information on the specific place of origin of the wine. Until 2018 the aim was to define a single set of quality criteria for a wine simply called Rioja, but now it's possible to designate a Rioja wine as "viñedo singular", or as a single vineyard. Clearly the objective is to allow a single vineyard to promote itself as both a high-quality yet uniquely different Rioja wine. It's mandatory that the wine grapes used can be traced exclusively to the vineyard (requirement of traceability), and that strict limitations on the minimum age of the vines and the maximum yields are respected. In addition there are rules concerning growing practices, harvesting and winemaking techniques that must also be applied. The organoleptic assessment (e.g. colour, taste,…) is also more demanding.

The criteria for the traditional
Reserva, and Gran Reserva have also been revised. The requirement for a red wine Rioja Reserva includes now a minimum period of 6 months ageing in the bottle following a minimum barrel-ageing period of one year. With the additional requirement that the entire maturing and ageing process must last at least 36 months. The requirement for a red wine Gran Reserva is now that it must be aged in the winery for at least 60 months, of which it must have spent at least 24 months in the barrel and at least 24 months in the bottle.


The rule book


But let's
start at the beginning, and work step by step through the rule book. The rule book is the Rioja Protected Designation of Origin Specifications (2020). Remember I'm only looking at red wines.

The rules start with the wine's
analytic and sensory characteristics.
This is followed by specific
vinification practices and imposed restrictions, including growing practices, vinification practices, and ageing.
There are also sections on the
geographic area, maximum yields, grape varieties, and other requirements, etc.

An important point is that official or reference analytical methods and techniques that should/must be used are often described very precisely. For example, the "
Office Internationale de la Vigne et du Vin" (usually abbreviated to OIV) lists 146 different analysis routines. The OIV published a Compendium of International Methods of Wine and Must Analysis - Volume I (2021) and Compendium of International Methods of Wine and Must Analysis - Volume II (2021).

It's worth mentioning that the Association of Official Analytical Collaboration claims to list more than 3,000 validated chemical and microbiological analysis methods.


On this webpage I have quoted directly from the Rioja regulations (
in bold and italics), and have tried to add what I hope are useful additional descriptions and explanations. My additions can be quite extensive, and I've tried to place them in the most logical place in the regulatory text, but it's not always that easy and there could be some repetition.


Rioja wine classification - analytic characteristics


Analytic characteristics are alcoholic strength, volatile acidity, colour intensity, sulphur dioxide content, residual reducing sugars, total acidity, pH, and over-pressure (only for sparking wines).

Analytic characteristics - alcoholic strength


The first analytic characteristic is alcoholic strength, which for a red Rioja wine must be a minimum of 11.5% (by volume).

There are a number of different types of
alcohol, and its ethanol (just one of the monohydric alcohols) that is naturally produced by the fermentation of sugars by yeasts.

Alcoholic strength is a standard measure of how much alcohol (ethanol) is contained in a given volume of the wine (expressed as a volume percent). The % vol. is a dimensionless quality, and is the same as a volume concentration, i.e. what percentage of the total volume is ethanol. It is not the same as mass concentration, molar concentration, or volume fraction (nor alcohol proof).

The simplest way to determine
alcohol by volume is by using a hydrometer, which is a device to measure specific gravity (or density of a liquid with respect to water, which has a specific gravity of 1.000). Prior to fermentation the wine contains sugars which will make the liquid more dense, and so the hydrometer will float higher in the liquid than in water and will therefore give a higher hydrometer reading (e.g. around 1.075-1.095 for wine). During fermentation the sugars are converted by the yeasts into alcohol and carbon dioxide. Alcohol in water is less dense than sugar in water and so this will result in a change in the specific gravity and the hydrometer will now sink further in the liquid compared to the earlier measurement. It will now have a specific gravity closer to water (e.g. around 0.990-1.000 for wine). Then dividing the difference between the two results by 7.36, yields the alcohol by volume (% vol.). Some hydrometers are pre-calibrated for wine and for a specific temperature, other hydrometers come with formulas and charts so that the readings can be converted into accurate results.

The Greek philosopher Archimedes discovered the physical principle of buoyancy. An instrument to evaluate the density of liquids, based on this principle, is the hydrometer, also known as aerometer and as a Archimedean balance. One story is that Archimedes uncovered a fraud by a craftsman who had made a crown of gold-silver alloy but claimed that it was solid gold. Archimedes's method and theoretical assumptions were closely studied by Galileo who in 1612 described a high-precision instrument, the bilancetta or "little balance", whose operation was based on the Archimedean concept of specific weight. Bodies weighed in water are found to be "lighter" than when weighed in air. The difference is proportional to the ratio of their specific weight to that of water. With the hydrostatic balance, we can therefore determine a body's specific weight relative to that of the liquid in which it is immersed. Alternatively, if we know the body's specific weight, we can determine its volume. The balance is a graduated glass cylinder which more or less floats (dips) in a liquid depending on its density. Hydrometers were being constructed in Florence to determine the density of different liquids, including the percentage of spirit in alcoholic beverages, and the density of spring waters. It was recognised that liquids changed density with temperature and savants tried to build thermometers with liquids. They tested various liquids, including water, ethyl alcohol, oil, and mercury. The volumetric expansion coefficient of ethyl alcohol is about ⅓ of that of the air, but is 6.2 greater than that for mercury, and 1.6 greater than that for oil. Water was rejected because of the risk of damage by frost. The preferred liquid at that time was pure ethyl alcohol because it had the largest expansion coefficient and the best instrument resolution. The main drawback was that it was poorly visible, and the addition of dies resulted in the staining of the glass tube, thus worsening the situation. Among the various thermometers, the most accurate and reliable one at that time was the Little Florentine Thermometer, with a scale divided into 50 Galileo degrees (1°G = 1.44°C). The main contributors to this invention were Evangelista Torricelli, and the first was built in 1641. Robert Boyle was in Florence in the same year, and later he studied the laws of gases using a replica of the Little Florentine Thermometer.

Hydrometer and Refractometer

The glass tube in the foreground is a hydrometer and the instrument in the background is a refractometer.

An alternative to using the
hydrometer is a refractometer, another simple instrument that can be used to measure the concentration of substances dissolved in a liquid (often called "total soluble solids"). When light hits the liquid, it changes direction, a phenomenon known as refraction. In the liquid, the amount of sugar affects its density, which affects how light is refracted. Depending on the density of the liquid, the angle of refraction is more or less pronounced. Refractometers work using this property and translate this shifted angle of refracted light using a graduated Brix chart that is visible in the eyepiece of the traditional handheld analog refractometer.

The
sugar composition of grape berries has a key role in wine quality, since it determines the alcohol content of the wines. During grape berry ripening, sucrose produced in leaves by photosynthetic carbon assimilation is transported from the leaves by the phloem, and at véraison begins to accumulate in the berry vacuoles as glucose and fructose (through an enzyme called invertase). Grape berry sugar composition and concentration changes during grape ripening and can be influenced by many factors, such as the environment (sun exposure, temperature, etc.) and viticulture management. Using visual clues, taste and measurements of the sugar level in the grapes, a grape grower will know when the grapes are beginning to mature, how ripening is progressing, and when the grapes can be harvested.

Brix is a measure of the soluble solids content in grapes, and each degree of Brix equals 1 gm of sugar per 100 ml of grape juice (there exist other sugar content scales similar to Brix). So a measurement of 20°Brix means the juice is 20% fermentable sugar, and multiplied by 0.55 gives a rough estimate of the amount of alcohol the resulting wine might have. Like hydrometers, refractometers can also be purchased with a variety of scales. Only a few drops are needed, but those drops need to be representative of both the grapes on that specific vine and all the vines in the vineyard. The measurement of refractive index is subject to temperature effects and therefore must be corrected for ambient temperature. There are also hand-held digital refractometers, many with automatic temperature compensation.

Once the grapes are harvested, measuring Brix of the
must is just as important since it is a way to track fermentation progress. As more sugars are consumed by yeast, the Brix reading will decrease. When a wine is fermented to dryness, the Brix reading will be below 0, suggesting that fermentation is complete. If Brix readings a day or two apart during fermentation are unchanged, this is a sign that fermentation could be stalled. Many texts note that hydrometers should be used during active fermentation because the ray of light in the refractometer is affected by the alcohol and carbon dioxide bubbles and the corrections are difficult to implement.

Theoretically,
yeast converts sugars into almost equal masses of ethanol and carbon dioxide gas. In reality some sugar is actually converted to energy and yeast cell growth, and some ethanol vapour is lost to the environment. So ethanol yields are only ever around 90% of the theoretical value. Brix (or Baumé) measurements are only a quick estimate (a "rule of thumb") of sugar content in a grape sample or must (i.e. 1 Baume equals 1.8 Brix, equals 1% potential alcohol). But this type of measurement (hydrometer) is a volume measurement, and does not actually measure a sugar concentration or sugar weight per unit volume. Instead it measures the specific gravity of a solution, e.g. the hydrometer displaces a volume of liquid, with the equivalent volumes calibrated at known sucrose concentrations. This is a good estimate because ripe fruit is 90-95% sugar, and the rest is pigments, tannins, organic acids, pectins, salts and non-fermentable sugars. Given that only fermentable sugars are converted to ethanol, you could measure the glucose and fructose concentrations rather than Baume or Brix, and then calculate a potential alcohol % by volume. It actually uses a conversion factor of 16.83 g fermentable sugar per litre for 1% v/v alcohol. The problem is that this conversion factor is highly yeast dependent and can vary from 16.5 g/l to 17.2 g/l, which could result in a determined alcohol concentration of between 14% and 15%. It's possible to calculate the exact conversion rate for a specific grape, yeast, and fermentation conditions. But why does the conversion factor change? Firstly, there could be less alcohol evaporation because the fermentation temperature was lower, or because the surface area to volume ratio of the tank was lower than usual. Secondly, aeration during fermentation will increase evaporation. Thirdly, nutrient levels will affect the fermentation rate in different ways depending upon the yeast strain. Fourthly, in hot years grape might be more shrivelled and have a higher solids/skins to liquid ratio, and it is then difficult to extract a representative liquid sample to measure, and more sugars are stored in the grape skins, i.e. the measurement will under-estimate the actual sugar content.

I think the message is clear. A
hydrometer or refractometer are very useful tools but they are not precise measurement tools. For example, EU rules state that the actual volume percentage of alcohol in a drink is only allowed to differ from what is stated on the label by ±0.5%. Logically, a winery needs an accurate on-site system for measuring alcohol levels (and other parameters, as we will see later on this webpage). There are a number of techniques available, some can be expensive, some require highly trained staff, so it's all about picking the right technique. I'm no specialist, but as far as I know you could use a more elaborate version of the density/refractometry method, or use a titration method, or use a ebulliometer (boiling point measurement), or one of several gas chromatography techniques, or a distillation technique, or near-infrared spectrometry (NIR), or Fourier-transform infrared spectrometry (FTIR), etc. There is also the problem of what technology could be used, against what technique and measurement procedure is recognised for regulatory compliance.

The
OIV documents a method for the evaluation of sugar concentrations in grape musts by refractometry (Method OIV-MA-AS2-02). The principle is no different from the hand-held refractometer seen above, expect that it is a Abbe refractometer, i.e. a laboratory instrument that when used with an appropriate table gives sugar concentration in g/l and in g/kg for grape must.

Abbe Refractometer Modern Abbe Refractometer

Newer instruments have replaced the system for circulating water to ensure a constant temperature with a Peltier device. There are automated instruments that measure at different temperatures and wavelengths, and process versions can be installed in-line in large industrial plants.

The
OIV documents two methods for determining the density and specific gravity of must or wine at 20°C. The first procedure for density measurements is when using pycnometry, or electronic densimetry using an oscillating cell, or densimetry with a hydrostatic balance (Method OIV-MA-AS2-01A). The second is when using areometry, which is simply the proper procedure for using a hydrometer to measure the specific gravity of must or wine (Method OIV-MA-AS2-01B).

A
pycnometer is a way to measure density, but in fact actually measures the mass of a fixed volume, and the density is calculated as the ratio of mass to volume (the pycnometer is the name given to the small glass measure with a fixed volume). Often the procedures are in fact relatively easy to perform, but not so easy to visualise, but there are plenty of video descriptions on the Internet.

The working principle of an
oscillation-type density meter is based on the law of harmonic oscillation. A oscillating U-tube of a constant volume at a given temperature, is completely filled with the sample to be analysed, and subjected to an electromagnetic force. The measuring cell consists of a hallow U-shaped tube of constant volume that oscillates at its fundamental frequency, which is a function of the system mass. If we assume that the sample volume inside the cell is constant, then the oscillation frequency is a function of the sample density. Translating the idea into a functional instruments required decisions about the oscillator type, the sensor material, the glass, counter-mass, temperature regulation, the pick-up, calibration, and the effect of viscosity (see article). This measurement instrument will be described in more detail later on this webpage.


Mohr-Westphal Modern Hydrostatic Balance

The hydrostatic balance is a modern version of a Westphal balance, also known as a Mohr balance, which was an early laboratory instrument for measuring the density of liquids. The original balance consisted of an arm first balanced with the plummet totally immersed in water at a known temperature. The plummet had a built-in thermometer and had a known volume and mass. The system was balanced, and then the plummet was completely immersed in an unknown liquid, and the system rebalanced. The series of riders on the beam gave the buoyant force of the liquid relative to water, and hence the specific gravity, which could already be obtained to four decimal places. The description today consists of a very precise balance and a sinker (e.g. a sphere) of exactly known volume that is attached to one scale pan. The sinker is immersed completely in the sample and the apparent weight loss of the sinker is determined by weighing out. The apparent weight loss of the sinker equals the weight of the fluid it displaces, so the precise volume and weight are known. Hydrostatic balances can be both reliable and precise. However they are expensive and very time-consuming. Another disadvantage is that installation (e.g. insulation on a concrete foundation) is challenging and an accurate temperature control is essential and is only possible by means of highly sophisticated air conditioning.

The
ratio glucose/fructose can be determined by an enzymatic method for sample preparation, and using a spectrophotometer measurement at the wavelength of 340 nm (Method OIV-MA-AS311-02). The absorption in the near-ultraviolet is maximum for a first reaction product (glucose), and then the measurement is continued for a second reaction product (fructose).

Spectrophotometers, and the interpretation of the data, are increasingly important for analytical laboratories working on environmental, biomedical and industrial monitoring. A spectrophotometric transducer is the heart of the analyser, since it converts an optical signal into a sequence of raw data representative of the spectrum, i.e. a signal x(λ) for a number of data points N, where λ is wavelength, x is light intensity, The wavelength values ​​cover a broader or narrower subrange [between λmin and λmax] of one of the following standard intervals:-
200 - 300 nm - middle-ultraviolet radiation (MUV)
300 - 380 nm - near-ultraviolet radiation (UV)
380 - 750 nm - visible radiation (Vis)
750 - 2,500 nm - near-infrared radiation (NIR)
2.5 - 10μm - middle-infrared radiation (MIR).

Below we have on the left the
transmittance spectrum, i.e. the intensity of the light by wavelength that passes through a red wine sample. On the right we have the 'opposite', i.e. the absorption of the light by the sample for each wavelength.

Transmittance of Red WineAbsorbance of Red Wine


The practicalities of a particular instrument, e.g. the
resolution of the optical grating and photodetector matrix, means that the spectrum of transmitted light is separated into a series of different optical signals corresponding to a narrow subrange of wavelengths. The machine converts the signals into a current that is proportional to intensity, which is then converted into a code or number for that wavelength. When compiled together the numbers create an intensity spectrum as seen above. The challenge is then to identify and estimate concentrations of the chemical compounds in the sample. The underlying spectral peaks of the chemical compounds present in the sample will be disturbed by noise and 'blurring' of overlapping peaks. The analysis is therefore based upon a calibration involving some spectral standards for the class of substances the machine is designed for. It is the absorbance data that is the most informative parts of the spectrum, because the absorption peaks (e.g. positions, magnitudes, etc.) determine the qualitative and quantitative composition of the sample. It is this spectrum that is often called a "finger-print" of the sample. For example, machines that focus on NIR part of the spectrum are often considered useful for food and drink analysis because the spectra of organic samples comprises broad bands arising from the overlapping peaks corresponding to C-H, H-O, and N-H chemical bonds. This makes NIR spectrophotometry a very rapid and simple analysis machine that often requires no sample preparation. In addition the relatively weak absorption due to water enables these machines to analyse high-moisture products and ingredients. The machines operate more or less as black-boxes, but they do require calibration.
A measurement spectrum might have 1,000's of data points, but the values for one wavelength are highly correlated with those of wavelength values next to them. This decreases the apparent information in the data collected, but this redundancy has its advantages. The key is the calibration with reference data, and the whole data analysis process is called
chemometrics. The best situation is where pure standards are available, and reference mixtures can be designed for calibration purposes.

The key message is that the position of the spectral peaks carry information about the compounds in the sample, and the magnitude of the peaks about their concentrations.

Instruments, designed for measurement of ethanol concentration and sugar concentration in wine, were used by wine makers already in the first half of the 19th century, and started to become routine tools after 1857 when Louis Pasteur explained the biochemical nature of fermentation. However, more complete analysis of wine had to wait ca. 100 years for the development of such modern analytical techniques as liquid chromatography (separation of mixture components) and mass spectrometry (elemental analysis). The age of spectrophotometry came in the early 1970's.
From chemical point of view, wine is a water solution of numerous (ca. 1000) organic and non-organic substances. The most important groups start with
glycerol, nonvolatile acids, phenols, minerals, sugars, amino acids, higher alcohols, volatile acids, etc.. We can immediately see how many parameters (variables) may differ in different wines, depending on their geographical origin, sort of grapes and technology used in their making. The task to be performed by a spectrophotometric wine analyser is to estimate those parameters or at least recognise them. The problem is spectra of different wines may not differ that significantly. However, there are now plenty of machines on the market that can routinely determine the concentrations of ethanol, glucose and fructose, malic acid, volatile acids, total acidity, etc. in both finished wine and must under fermentation.

We have quickly mentioned just one of the analysis tools that are available today. Others permit the determination of the elemental composition of wine, some of which (e.g. As, Pb, Cd) are toxic. Other techniques are used to better understand the fermentation process, others for detecting the illicit addition of sweeteners, or the presence of pesticide residues, etc.

It is possible to directly measure the
dosage of sugars in wine using high-performance liquid chromatography (Method OIV-MA-AS311-03). High-performance liquid chromatography is a specific form of column chromatography generally used to separate, identify, and quantify the active compounds in a mixture.
Column chromatography is a popular way to separate and purify a single chemical compound from a mixture dissolved in a fluid. It exploits the chemical nature of compounds which are
adsorbed and eluted based on their differential absorption in an adsorbent. Column chromatography consists of a stationary solid phase that adsorbs and separates the compounds passing through it with the help of a liquid mobile phase. The compounds move through the column at different rates which allows them to be separated in fractions. The components with a lower affinity to stationary phase travel faster than those with a greater affinity for the stationary phase. The components that move faster are removed first, whereas the components that move more slowly are eluted last.
Various stationary phases, such as
silica, alumina, calcium phosphate, calcium carbonate, starch, and magnesia, and different solvent compositions based on the nature of compounds to be separated and isolated, are used in column chromatography. In column chromatography, a cylindrical glass tube, which is plugged at the bottom by a piece of glass wool or porous disc, is filled with slurry (adsorbent) and a suitable solvent. Samples to be separated are mixed with silica and introduced at the top of the column and allowed to move with the solvent. With polarity differences, compounds are adsorbed at different regions and desorbed with suitable solvent polarity. The compound of higher adsorption ability will be adsorbed at the top and that with the lower one will be at the bottom. By adding the solvent at the top, compounds get desorbed and pass through the column and this process is called elution.

Column Chromatography

What "high-performance" liquid chromatography does is utilises a column that holds packing material (stationary phase), a high-pressure pump that moves the mobile phase(s) through the column, and a detector that shows the retention times of the molecules. The high-pressure pump is used to overcome the flow resistance when the stationary phase packed in the column are small particles. The high-efficiency is due to the small and uniform size of particles. Retention time varies depending on the interactions between the stationary phase, the molecules being analysed, and the solvent(s) used. The sample to be analysed is introduced in small volume to the stream of mobile phase and is retarded by specific chemical or physical interactions with the stationary phase. The amount of retardation depends on the nature of the analyte and composition of both stationary and mobile phase. The time at which a specific analyte elutes (comes out of the end of the column) is called the retention time. Common solvents used include any miscible combinations of water or organic liquids (the most common are methanol and acetonitrile). There are several ways to detect when a substance has passed through the column. Generally UV spectroscopy is attached, which detects the specific compounds. Many organic compounds absorb UV light of various wavelengths. The amount of light absorbed will depend on the amount of a particular compound that is passing through the beam at the time. The output is recorded as a series of peaks, each one representing a compound in the mixture passing through the detector and absorbing UV light. The area under the peak is proportional to the amount of substance passing through detector, and this area is calculated automatically and displayed. This is another procedure that not easy to visualise, but there are plenty of video descriptions on the Internet.

HPLC Parts

The basic instrument components are called a chromatograph, and they are a sample injection, a high pressure pump (a), a solvent injection (b), sample injection (c), the analytical column (d), the detector (e), and data acquisition (f).

It would be a mistake to view chromatography as a 'simple' laboratory instrument, whereas chromatography columns is in fact an industrial tool that in 2019 was worth nearly $12 billion, and the market is projected to be worth over $16 billion in 2026. For example, it is a key tool in the development of therapeutic vaccines.

Now we turn to the real topic of this section, the measurement of
alcoholic strength by volume.
The
OIV describes two methods for determining the alcoholic strength by volume. On the surface both procedures look very similar to the two documents issued by the OIV for the determination of the density and specific gravity of must or wine at 20°C. However there is one common addition in both documents, they both include an initial distillation of the wine that was first made alkaline (i.e. basic) by a suspension of calcium hydroxide.

In the first document for the
alcoholic strength by volume, the same measurement techniques, a pycnometer, a oscillating U-tube, and a hydrostatic balance, are used, but now on the distillate (Method OIV-MA-AS312-01A).

The second method for
alcoholic strength by volume not only makes reference to the use of a hydrometer but also describes the use of a refractometer, both again applied to the distillate (Method OIV-MA-AS312-01B).

The procedures permits any type of distillation apparatus, including
steam distillation, to be used provided that it is tested five times with an ethanol-water mixture with an alcoholic strength of 10% vol. and the losses of alcohol during each distillation are not be more than 0.02% vol.

Distillation is the benchmark for many analysis procedures, and is officially approved by excise authorities in most countries, particularly when any form of litigation is involved. It involves a sample being prepared and the distillate (the product of the distillation) being measured using one of the methods already outlined for the measurement of the density and specific gravity of must or wine at 20°C, and including the use of a refractometer as an additional measurement technique. So effectively the technique involves the determination of the specific gravity of the distillates, and as far as I understand things the preferred measurement technique appears now to be the oscillation-type density meter based on the law of harmonic oscillation.

The alcoholic strength expressed in percent by volume (% vol) is one of the oldest parameters for which quantitative analytical methods have been developed. The foundations for the determination of alcoholic strength were laid down by Gay-Lussac (1776-1850), who not only invented a simple-to-use centesimal alcoholometer (i.e. a hydrometer with a '% vol' scale) but also provided the theoretical background in 1824. For this reason, the percentage by volume is also called the French or Gay-Lussac system. The major impetus for standardising the determination of alcoholic strength was to provide a consistent method for the collection of alcohol taxes (the Gay-Lussac system was already obligatory in France in 1884). Today the indication of alcoholic strength by volume using the symbol '% vol.' is mandatory on labels of alcoholic beverages in the whole European Union. Strictly speaking the term alcoholic strength is preferred over 'ethanol content/concentration' because the measurement is based on densimetry, and a small part of the alcoholic strength is always constituted by other alcohols (mainly methanol) besides ethanol.
While hydrometer-type alcoholometers are still widely applied in industry, they do not have the accuracy needed in a laboratory setting, especially for the purpose of controlling the relatively strict tolerances allowed by EU law for the indication of alcoholic strength in the labelling. For this reason, pycnometric determination of the density was for a long time the only approved reference method to determine the alcoholic strength in spirits and wines. The densimetric measurement typically has to be preceded by a distillation step, because sugars and other solutes would otherwise lead to false results, as the tables for converting density to alcoholic strength are based on pure water-alcohol mixtures.
In the 1980's, electronic densimetry, which is based on electromagnetically-induced oscillation of a U-shaped glass tube, was introduced into the analysis of alcoholic strength. This method showed similar or better performance in terms of accuracy and precision in comparison to established methods like pycnometry, hydrostatic balance or hydrometry. Today sample preparation by distillation followed by some form of density measurement (i.e. pycnometry, electronic densimetry and densimetry using hydrostatic balance) is still considered the gold standard and the reference methodology for determination of alcoholic strength, and figures in the compendium of international methods of wine and must analysis by the
OIV.

While all these densimetric methods have the advantage of being based on Gay-Lussac's principle and therefore yielding directly comparable results, they are relatively time-consuming. They also require special training of personnel if reproducible results are to be obtained, because errors can occur during distillation steps and subsequent densimetric measurements. Other techniques can be used, for example, spectroscopic methods are attractive because they can be used without any sample preparation steps (i.e. without distillation). Some instruments can measure for several different compounds in wine in less than 2 minutes per sample, however they require a relatively large investment which is prohibitive for smaller laboratories and small-scale wineries.

As mentioned above the distillation step before the densimetric measurement is crucial as it separates volatile compounds and non-volatile substances (i.e. removes sugars and other solutes) that would lead to inaccurate results, as the conversion of density to alcoholic strength is performed based on tables using pure water-alcohol mixtures as a reference. Again as mentioned above traditional distillation is time-consuming and requires several manual operations, whilst semi-automated steam distillation is a faster procedure where the steam flows expel the alcohol from the sample in less than 10 minutes, a considerably shorter time compared to the traditional distillation process. There are a number of commercial application notes on the web that describe in detail the measurement procedure, see this example for Method OIV-MA-AS312-01A using a pycnometer. Below we have a example of an automated laboratory steam distillation equipment described in a 2015 publication entitled "Improved automatic steam distillation combined with oscillation-type densimetry for determining alcoholic strength in spirits and liqueurs" (an example of Method OIV-MA-AS312-01B).

Automated Steam Distillation Device

This is an automated steam distillation instrument setup for the determination of alcoholic strength in spirits.
1 - Quick clamping device with clamping block
2 -
Kjeldatherm digestion tube with sample
3 -
PTFE steam inlet tubing
4 - Viton connection stopper (
FKM O-ring)
5 - screw caps
6 -
NaOH inlet (closed with blind cap for alcohol distillation)
7 - glass distribution head
8 - screw cap
9 - glass distillation condenser cooled at 10°C
10 - screw cap
11 - ventilation valve
12 - control panel
13 - standby switch
14 -
USB interface
15 -
silicone outlet tubing for distillate discharge
16 - graduated flask as receiver (filled with small volume of water, in which the outlet tubing must be submerged)
17 - receiver table
18 - drip tray.


Another commercial application note describes density measurements, including
hydrometers, pycnometers, hydrostatic balances, and digital density meters. The digital density meter has already been mentioned. It is based on the oscillating U-tube principle, i.e. a U shaped glass tube, which is excited and starts to oscillate at a certain frequency depending on the sample. Determining the frequency, the density of the sample can be calculated. From 1967 to 2018, all benchtop density meters worked according to the “Forced Oscillating Method” of the U-tube principle. From 2018 the "Pulsed Excitation Method" is also available.
The first method just keeps the measuring cell continuously oscillating at a characteristic frequency. By recording this constant oscillation not only the frequency of oscillation but also damping can be measured. The newer method evaluates the oscillation pattern including an interruption of the characteristic frequency that leads to a natural fade-out of the oscillation. This procedure is repeated continuously and allows evaluation of the fade-out behaviour of the oscillation. A series of values is obtained which not only allowed for a viscosity correction but also checks the repeatability of the density result, and improved detection of sample inhomogeneity (e.g. gas bubbles).
The digital density meters has become the preferred instrument because it provides a fast and precise measurements of fluid densities over a wide range of temperature and pressure. They measure the true density (density in vacuo), so there is no influence of air buoyancy or gravity. In addition, in contrast to traditional static methods (such as hydrometers, pycnometers, or hydrostatic weighing) only a small amount of sample is needed, approx. 1 ml to 2 ml, and they are easy to operate and don't require any special requirements regarding ambient conditions or temperature control. Modern high-precision density meters additionally provide a
viscosity correction even viscosity determination and a reference oscillator to enable accurate results over a wide range of densities, temperatures, and viscosities.

Oscillating U-tube Measuring Method

Above we can see the basic components:-
The
sensor is the key element and can be a straight or U-shaped tubes, made of borosilicate glass glass, metals or metal alloys, or even plastics depending on the required resistance towards the sample and cleaning agents.
A
countermass is linked to the measuring tube to reduce parasitic resonances (“external oscillations”) from other components, e.g. electronic parts.
Glass sensors have a built-in
reference oscillator which eliminates not only long-term drifts due to the ageing effects of the material but also temperature changes that influence the elasticity.
Temperature regulation of the cell is typically performed with Peltier elements, which have now displaced water baths.
Excitation can be with a system of magnets or with a Piezo element.
The
pick-up of the oscillation signal can be with optical pick-ups that detect a light beam that is interrupted by a minute coating on the oscillating tube. The alternative is with Piezo elements, which can be used to both excite and detect the oscillation. Magnets can also be used to measure the period of oscillation as well.
Today
digital signal processors (DSP) are used to analyse the oscillation signals.


For protected wines to have the right to bear the name of geographical units that are smaller than the region or the zones "Rioja Alta", "Rioja Oriental" and "Rioja Alavesa", or that of a minor geographical entity included in one of these zones, such as municipalities, in addition to having been made in their entirety with grapes collected in the territorial area of the relevant zone or minor geographical entity, must also meet the following analytical requirements:


Exceptionally, a wine may be considered to come from the area or from the municipality if its vinification includes no more than 15% of grapes from registered
vineyards in municipalities bordering the area or municipality where the operator is located and provided that it is accredited by legally valid title, that such operator has had that 15% of grapes at its disposal for no less than 10 years.

The red wines with the right to
Reserva and Gran Reserva indications must have a minimum actual alcoholic strength of 12% (by volume).

The previous regulatory system (
Consejo Regulador) for Rioja wines used oak-ageing as the primary indication of quality. The new regulatory system now also allows wineries to mention both regional microclimates and singular vineyard sites. The three official growing zones still exist, namely Rioja Alta, Rioja Oriental and Rioja Alavesa, as do the four ageing classifications, namely Joven (young), Crianza (aged), Reserva, and Gran Reserva. All Rioja wines are a blend of grapes from anywhere in the growing region, and the assumption was that regional specificity did not impact on the quality of the wine. Below we can see the tradition seals used for Rioja wines.

Rioja Tradtional Labels

However, the new regulatory system has changed the definition of a Rioja wine from a particular zone, i.e. "vinos de zona". Now the main requirements for these wines is that the winery be located in the area designated on the label and that at least 85% of the grapes come from vineyards in that geographical area. The rest can be brought from vineyards in neighbouring towns, always proving that the same supply of grapes will be available for an uninterrupted period of at least 10 years. In addition to displaying the name of the area on the front label, these wines will bear the letters "VZ" on the seals of the Regulatory Council, which certifies their traceability.


New Rioja Classification System

In addition, Rioja wines can now add the name of the village/municipality on the front label (Vinos de Municipio o Pueblo), or even limit production to a single vineyard (the so-called Viñedos Singulares). The truth is that some commercial brands of wineries already made reference to historic vineyards or specific places, so what the new regulations have done is to make an asset out of an existing reality. The novelty is that now, those who adopt the category of Viñedos Singulares will have to demonstrate that the grapes are indeed born in the vineyards to which they refer. They will also have to test the specificity of the vineyard and the quality of the product, requirements that go beyond other models that only focus on the soil or on the limitation of yields. For the consumer, a wine labeled as Viñedo Singular will be a guarantee of a particular quality and origin as evaluated and verified by the Regulatory Council, however it does not necessarily mean that it is better than another "classic" Rioja blend.

Clasificacion Vinos Rioja

"Vinos de Municipio" were already recognised from 1999, but in the new regulation they are more strictly defined. The winery (production, ageing and bottling) and the vines themselves, must be situated inside the village or municipal boundary. There is a possibility to include up to 15% of the grapes from a neighbouring vineyard, provided that it is under the control of the winery for at least the next 10 years. The wineries are also obliged to differentiate "Vinos de Municipio o Pueblo" and "Viñedos Singulares" from other wines being produced at the same time, and that separation must include also ageing and storage (i.e. totally separate physical processes and facilities). These wines will bear the letters VM on the seals of the Regulatory Council, which, as in the previous case, proves their traceability.

Viñedos Singulares

Above we can see that 'Rioja Alta' is the zone wine identifier, meaning that the grapes come from that area. Vino de Cenicero is the municipal wine identifier, meaning that the grapes come from that municipality. We see mention of Finca Carrasol, which is a Viñedo Singular, and the rule is that the name may not be bigger than 'Rioja' in typography or thickness. It is here that other allowed definitions can be displayed, e.g. I've see 'Viñedos de Altura' mentioned to describe high-altitude vineyards.

The Regulatory Council approved new Rioja wine labels containing an express reference to new production methods or characteristics of the vineyards, provided that there is real verifiable traceability. It still protects the traditional mention of ageing (crianza, reserva and gran reserva), and expressly prohibits any mention of wood or oak if it does not use the traditional type of barrel (225 litres) and minimum ageing periods, as well respecting the traditional zones and municipalities. The Regulatory Council has been faced with a variety of terms such as 'madurado en bodega' (matured in the cellar), 'las selecciones especiales' (special selections), 'los viñedos viejos y de altura' (old and high-altitude vineyards), 'la propiedad de viñedo y bodega' (vineyard and cellar ownership). Or just 'nuevos métodos de elaboración (lías, hormigón, tinajas…), meaning new production methods (lees, concrete, jars...).

The Regulatory Council did not accept 'single vineyard' because of the confusion it can create with Viñedo Singular wines. The also did not accept the names of certain municipalities, because the wineries didn't guarantee the traceability of the grapes used. Another problem is the expression 'Bodega ubicada en…', meaning 'Bodega located in...' (the name of the municipality). The problem here is that the bottler might be located there but it might not mean that the grapes come from that municipality.

Regarding geographical indications, ill-defined locations or even regions such as 'Sierra de Yerga' or 'Sierra de Cantabria', 'Toloño', etc., are already being used. Since only municipal and regional wines are mentioned in the regulations, there is no legal basis why this other indicators can't continue to be used.

The new labelling continues to protect the traditional mentions of ageing (crianza, reserva and gran reserva). However in the past, some wines have been called 'semi-crianzas', meaning a short stay in the barrel, but not reaching the minimum times required by the regulations. Producers suggested 'cellar matured' (Madurado en bodega) to refer to the fact that they were not young wines. At the time the Regulatory Council agreed to the term, but prohibited any use of 'for xx months'. The subject is controversial because there are several wineries that also use 'matured six months in the cellar...'. However any combination mentioning barrels, oak or wood on the labels is still prohibited, as are any drawings or designs on the label showing barrels, etc.

Special selection, family selection, vineyard selection, collection, limited edition, limited series... are terms that are often found on labels. The Regulatory Council allowed these descriptions provided they describe what the selection consists of and the number of bottles in the batch.

For the first time 'vi
ña vieja' (old vineyard) is regulated and the limit has been established at 35 years, which is the same as the minimum age for the new category of Viñedo Singular. It will also be allowed to indicate 'centennial vineyards' and even 'pre-phylloxera' (some vineyards still exist), but it will have to be proven. It is also authorised to indicate on the label 'Vineyard of more than x years', but that cannot be used on labels of bottles produced with younger vines in the same vineyard.

'Viñedos de Altura' (high altitude vineyards) are for vineyards above the altitude of 550 meters. The term has been used in the past for some old vineyards, and it is a term that has become fashionable and is looked for by consumers. The average altitude of the vineyard can be around 490 meters, but approximately 30% of the vines must be above 550 meters.

'Viñedos en propiedad' is a challenge given that more than 80% of the Rioja vineyards are owned by winegrowers. The problem is that most of them do not bottle. The Regulatory Council decided that traceability must be proven, that the wine must actually come from vineyards owned by the winery (or the business group). If not, a legal title must be accredited that guarantees the availability of the vineyard for a minimum of ten years. It is the same formula, in terms of ownership or fixed lease, which is required, for example, to be able to produce and label a wine as Viñedo Singular.

'Embotellado en la propiedad' (bottled on the property), should mean what it says, and not 'bottled for…' or 'bottled by…'. The mark or brand must be owned by the winery or the business group, and if its a business group they must also own the bottling facilities and it must also be registered with the Regulatory Council (i.e. in the Rioja region).

Nuevas elaboraciones' (lías, hormigón, tinaja…) meaning 'new elaborations using lees, concrete, jars…, are permitted if true. So terms such as 'fermented on
lees' (fermentado sobre lías), 'fermented in concrete' (fermentado en hormigón), 'elaborated (macerated) in a clay pot' (…elaborado (macerado) en tinaja de barro), etc. may be used on the labels when, for traceability, the winemaker can demonstrate that the wine has really been made in that way or using that specific technique.

Viñedo Singular Rioja

The rules for "Viñedos Singulares" requires that the vineyard is at least 35 years old, that the grapes are entirely hand harvested and that an independent tasting committee must note the wine as 'excellent'. In addition, the winery must prove that the exclusive production from that vineyard will be available for a minimum period of 10 years without interruption, e.g. leases on rented vineyards must be valid for at least 10 years, etc. There is also a maximum permitted yield of 5,000 kg/ha for red varieties, and a maximum grape-to-wine ratio of 65%. Only one "shoot topping" is allowed, i.e. the thinning and spreading out of shoots, gives every bunch of grapes more space to grow and ripen, and has a positive effect on grape yield and quality (e.g. cluster weight and number, cluster tightness, cluster length and width, berry weight, total soluble solids, titratable acidity and maturity index). In addition it avoids early bunch stem necrosis, and helps make the vines more resistant to both water stress and diseases. Not being an expert, I'm not sure of the subtile differences between green pruning, bud-rubbing, tucking-in, tipping, topping, leaf stripping, etc., but the objective is to favour sustainable viticulture, and limit vigour and vegetation growth during grape ripening. In any case a specific winegrower card is issued which defines all the allowed cultivation practices that must be respected (i.e. vine training, canopy management, etc.). Only then can Viñedos Singulares be combined with the current Rioja labelling rules on barrel-ageing, and in addition producers are allowed to include their own seal in which the words "Viñedo Singular" appears in capital letters (but always smaller in typeface and size than the word Rioja).

Analytic characteristics - volatile acidity


The second analytic characteristic is volatile acidity of the harvested wines, expressed in acetic acid, which may not exceed 0.05 g/l, for each actual degree of alcohol and may not in any case exceed 0.8 g/l for a red wine.

Volatile acidity is a measure of the low molecular weight (or steam distillable) fatty acids in wine and is generally perceived as the odour of vinegar (i.e. acetic acid). Winemakers are usually most concerned with acetic acid, which accounts for more than 93% of steam distillable acids in wine. The volatile fatty acids found in wine consist primarily of short-chain fatty acids (tails of less than 6 carbons) and medium-chain fatty acids (tails with 6 – 12 carbons). Yeast produces acetic acid during fermentation and much depends on the yeast strain and vigour of fermentation (e.g. temperature and juice nutrient status). Excessive acetic acid production is usually an indicator of microbial spoilage. However an unspoiled wine will always have some level of volatile acidity (e.g. 200-400 ppm), and it can be expected to increase in barrel-aged wine after one year. There is no given "threshold of detection" for volatile acidity, since the perception of these compounds can differ between wines, given that high levels of sugar, and ethanol mask them. However there are indications that volatile acidity is not easily detected below about 0.7 g/l, but above this level wine aroma starts to be affected and flavour starts to deteriorate, such that at acetic acid levels of 0.9 g/l and above, the wine has a noticeable "harsh", "bitter" or "sour" aftertaste.

The classical measurement technique involves firstly removing any
carbon dioxide from the wine, and then separating the volatile acids by steam distillation and titration using the strong base sodium hydroxide (Method OIV-MA-AS313-02). Given that other acids can contribute to volatile acidity, many wine laboratories just analyse directly for acetic acid (Method OIV-MA-AS313-27). This alternative test is quite straightforward, requiring only sample filtering and dilution, and the use of ultraviolet-visible (UV-Vis) spectrophotometer to measure the absorbance at a wavelength of 340 nm resulting from the generation of a by-product of the reaction (i.e. NADH which has a maximum absorption at 340 nm). NADH (nicotinamide adenine dinucleotide) is a coenzyme (organic molecule) which carries hydrogen atoms from the fermentation media and helps the ADH (alcohol dehydrogenase) enzyme incorporate a proton into acetaldehyde, creating ethanol as the final product of alcoholic fermentation. It is the concentration of the reduced form of the coenzyme (NADH) formed that is photometrically monitored at 340 nm.
Acetic acid in wine can also be measured using high-performance liquid chromatography (HPLC). However, the equipment requires a fairly high initial investment and skilled personnel, so it is really only feasible if the winery is using HPLC for other tests.

Analytic characteristics - colour intensity


The third analytic characteristic is colour intensity. The minimum colour intensity for red wines (A420 + A520 + A620) is 3.5 if there was malolactic fermentation (maximum 0.5 g/l malic acid) and of 4 if there was no malolactic fermentation, and minimum total polyphenol index 30.

We all know that
colour is our visual perception of properties we call red, blue, yellow, etc. However, intensity is a more complex term which we might associate with the brightness, i.e. our visual perception of the light emerging from, or being reflected by, a source (in this case, some red wine in a glass or sample holder). But given that the implication is clearly pointing to an analytic measurement we will need to look more carefully at the expression colour intensity.

But first let's look at
what "polyphenol index 30" means. This refers to naturally occurring phenols and polyphenols, which are a large group of several hundred chemical compounds that affect the taste, colour and mouthfeel of wine. In wine they determine many of its sensory properties such as appearance, colour, astringency, bitterness, and flavour, and also its stability through subsequent oxidative processes. One category, flavonoids, includes both anthocyanin and tannins. The content of polyphenols is greatly influenced by a number of different factors, i.e. the type of grape used, the technological practices to which the grapes are exposed, the type of yeast used in the alcoholic fermentation, and the contact with solid parts of the grape during the maceration. For example, during the growth cycle of the grapevine sunlight increases the concentration of phenolics in the berries, thus the importance of canopy management. In the winemaking process, maceration or "skin contact" increases the concentration of phenols in the wine, and oak-ageing can introduce vanillin, another phenolic compound (i.e. an additional vanilla aroma). There are several ways to measure total polyphenol but it would appear that here the reference is to what is often called the polyphenol index I(280), the measure of the absorbance at a ultraviolet wavelength of 280 nm using an ultraviolet-visible (UV-Vis) spectrophotometer, a type of absorption spectrometer. The strong absorption band around 280 nm is a feature of flavanol monomers, and is also common to all phenolic substances. In this assay, the total phenolics value is approximated by subtracting a constant value from the acidified, diluted sample absorbance value at 280 nm to account for interference from other compounds that also absorb at 280 nm. Even though these procedures are simple to perform, the value of the numbers obtained is questionable. Nevertheless, these analytical techniques are widely practiced in wineries.

Check out this article "
Grape and Wine Phenolics: History and Perspective".

The
colour of wine is probably the most easily recognisable characteristics of wines, and it is one element in the classification of wines. Even as early as the 1630's it was recognised that you judged a good claret using "the eye for colour and insistence, the tongue for the taste, the nose for the savour". Interestingly, some of the early work on naming propriety colours actually used "wine" as a name for a particular colour, i.e. with mauve wine, old wine, plum wine, port wine, purple wine (including dark and deep), raspberry wine, red wine, yellow wine, rose wine, ruby wine (light garnet), garnet was considered the same a Spanish wine, strawberry wine, blackberry wine, cherry wine, claret wine, dark wine, grape wine, light wine, wineberry, and last but not least both "lees of wine" and "dregs of wine", which were both considered the same as the colour maroon. In a more recent study based upon text mining, it was found that by far the most popular wine colour descriptor was just "red", whilst in the top 25 descriptors "cherry", "blackberry", and "plum" could be used to describe both colour and taste. In a German wine making manual they offered "brick red, ruby red, garnet, violet red, deep red verging on black, brownish red" as colour qualifiers for red wines. Both the European Brewery Convention (EBC) and the American Society of Brewing Chemists have standards for determining the colour of their beers. Both have standardised on 430 nm as the measuring wavelength, but in both cases there are visually different beers that have the same absorption. This situation is amplified by the arrival of craft brewing, beer-based mixed drinks, and alcohol-free and low-alcohol-content drinks. The EBC has a scale running from 4 for pale lager/pilsener through to 79 for imperial stout, whilst the US based "Standard Reference Method" runs from 2 to 40+ for the same range of beers. Interestingly, the "International Standard for the Labelling of Wines" only mentions the colour of a wine as an optional indication on labels.

The
red colour in wine comes from a pigment called anthocyanin, which is present in many other fruits, including plums, blueberries, and cherries. It is also found in flowers (like orchids, hydrangeas, etc.). The pigment in red wine comes from the skins of grapes. By soaking the skins in the juice, anthocyanin is released and it literally stains the wine. Anthocyanins degrade at higher pH and can be used as a kind of pH indicator, for example:-
  • Wines with a more red coloured hue have a lower pH (higher acidity).

  • Wines with a violet coloured hue range around 3.4–3.6 pH (on average).

  • Wines with a more blueish tint (almost like magenta) are over 3.6 pH and possibly closer to 4 (low acidity).


Different red grape varieties produce different levels and expressions of this group of pigment compounds, making the science behind it very complex. Wine Folly (see chart below) notes that there are hundreds of red wine varieties, but just 32 varieties make up the majority of the wines available in the marketplace. "Boldness" is a combination of several fundamental traits in wine, e.g. the tannin level in wine indicates boldness, and so does the alcohol level. Wines with lower alcohol, less tannin, and higher acidity are lighter-bodied, whereas higher alcohol wines tend to taste bolder, i.e. filling the mouth with a richer, rounder, possibly more creamy taste. Also as a general rule, wines with red fruit flavours tend to be lighter-bodied, and those with black fruit flavours tend to be fuller-bodied.

Red Wine Boldness

It is possible to make a qualitative assessment of the hue (colour) of a red wine by looking at it under natural lighting conditions (daylight illumination from above) and over or against a white background. Pouring a small amount of wine in the glass and tilting it at 45° away from the viewer allows the light to pass through the wine, and reveals the different red shades with more precision. Hue is just one of six appearance parameters, the others being lightness, brightness, chroma, colourfulness and saturation.

Colour Hue Expression

Tilting a glass of red wine against a white wall, window, or candle might look a bit arbitrary. But winemakers dedicate a lot of attention to coaxing the colour from their grapes, so we should also spend some time observing, smelling and tasting a good wine, and not just swig it down and ask for a re-fill. And remember visual appearance and colour profoundly affects the way we smell things, and that also then affects the way we taste things.

The most important thing to remember is that wine has no
colour unless it is illuminated, that is why it is so important to keep some kind of standard for the illuminant so that the observer can evaluate the colour seen. Fortunately hue (the colour) changes the least across a tilted glass of red wine, whilst the brightness we perceive (the light that appears to shine from something) is strongly related to the path-length (thickness) of the span of wine being viewed. So the most important correlation is between the hue at the rim (shortest path length) and age, and it is this hue that is best used to classify the wine's colour. Above we can see the best place for viewing the colour of a wine, and the area represents only about a 10° visual field.

The scientific reality is that tilting the glass against a white background can be a bit arbitrary, so I suppose the practical requirement is to self-calibrate, looking at different wines and trying to keep similar viewing conditions (e.g. type of lighting, background and viewing geometry). Two things worth remembering when viewing wine in this way is that both
contrast and colourfulness increase with luminance (the "Stevens effect" and "Hunt effect" respectively), so as the level of illumination decreases, the ability to recognise and discriminate between degrees of colour differences rapidly decreases. It is equally true that holding the wine glass up to the sun will wash-out all colour variations, so the "best" illumination is probably lightly overcast daylight or any bright but diffused, full-spectrum white light source, and a neutral white background. Different types of illumination can make a wine look completely different, and the perception of hue (colour) of a wine usually leads to naming the colour of the wine (e.g. ruby, garnet, raspberry, etc.). White wines appear reddish-yellow under incandescent lighting (common in restaurants and homes), but greenish-yellow in the daylight (the recommended lighting, but almost never used), and they then progress back to more of a yellowish colour under the other types of lighting. Red wines are even more changeable, where one varietal under one illumination can be easily confused for another varietal under another illumination. Specifically, the illuminants with less long-wavelength content, although still appearing bright and white, will make red wines appear significantly darker. Saturation also has significant dependency on the illuminant. The fluorescent lamp (sometimes recommended) and the earlier blue-pumped LED significantly desaturate the red wines (they look less red) compared with the standard incandescent lamp, daylight, or the more recent high-quality RGBA LED.

Whilst being rather subjective it's possible to use a kind of standardised vocabulary to describe the red colour (
hue) of wine, and even associate with that colour a specific variety of wine grape. However, most of the anthocyanin (the colour pigment in red wine) is lost after 5 years of ageing, and older red wines loose colour as they age, turning more garnet and eventually turning brown. Oxidation in wine also causes it to become brown over time. Higher levels of tannins make wines more opaque, whereas higher sulphite additions reduced colour intensity.

A
colour term is a word or phrase we use to refer to a specific colour, and generally we use names that are monolexemic (i.e. consisting of a single lexeme having a certain meaning and being an emic unit or type of abstract object). In addition we want names that can't be confused with other colour names, and can be applied to any type of object. We mean abstract in that we should try not to use a basic colour term that is also the name of an object that has that colour. Equally important is naming easiness, or "nameability", a colour space where there is no confusion about the name to be assigned to each colour. We can all decide that red, green, blue, yellow, black and white are the most important, but what about brown, orange, purple, pink or grey? The next problem is that whilst we can maybe accept these eleven colours, in real life we encounter a multitude of objects, etc. that don't quite fit to any of these eleven colours. So the next step, might be to introduce degrees of lightness, with very light, light, medium, dark and very dark, and/or saturation with greyish, moderate, strong and vivid), and then we can create an number of lightness-saturation combinations, with for example, pale for light-greyish, brilliant for light-strong, and deep for dark-strong. And we can always stick "ish" on the end to obtain, reddish, greenish, etc. This kind of analysis led to a set of 312 possible colour names in the Munsell colour system, a colour space that tries to define our perception of colour based upon hue (basic colour), chroma (colour intensity) and lightness (our perception of luminance). The original work of Munsell was in defining the colour of soil, and there exists a soil colour book with examples covering an amazing variety of subtile differences in soil colour.

Returning to the basics, another view was to keep seven chromatic terms (red, orange, brown, yellow, green, blue, and purple), and three achromatic terms (white, grey and black). Adding to this some terms for
lightness-saturation yielded 627 different colour names (with only 340 of them found in the Munsell colour book). But some of the possible colours were not that intuitive, e.g. very light greyish greenish-blue.

With the advent of the computer display and graphical interfaces there was a need for a new set of colour names for computer applications. Today this has led to the use of millions of colours, but has not really helped us understand what to call different colours of red wines. This is all the more true when it quickly became apparent that different types of illumination had a major impact on our perception of colour, and on top of that the results of experiments appeared highly conditioned by what rules were imposed (e.g. were terms such "lightish red" or "purplish-red" allowed, and if so, what did they mean).

This may appear somewhat academic, but already in the 1930's it became evident that wines with a stronger more intense
colour were more desirable, and therefore more expensive. That early analysis was based on Chevreul's method, using only five purple-reds and three shades of pure red. Already some of the earliest work on the colour of red wine, was focused on colour intensity and not the actual colour (hue). The idea was to define a unit of low magnitude for the red colour, so that all wines would be greater in magnitude. The lowest "colour" unit was a pre-defined mix of chemicals, against which the wine would be diluted until it matched it. So a "good" red wine was more than ten "colours", i.e. a dilution of nine parts water to one part wine, obtained the colour intensity of one "colour" unit. Later technology replaced the human eye, and the "ROB" became the standard. "ROB" was the optical density at a given wavelength (usually 460 nm), multiplied by the colorimeter calibration constant using crystal violet. And rosé wines had a "ROB" of between 15-50, and red wines between 50-115.


It was in the early 1950's that the maximum of spectral absorption for red wines was established at 520 nm (often written A520), and somewhat later the ratio A420/A520 was used to characterise red wine colour.

Absorption Spectra for White and Red Wines

Above we can see the typical absorption spectra of white and red wines (left and right respectively). There are specific particularities in the shape of the wine absorption spectra that are exploited for wine colour analysis. White wines exhibit a peak of the absorption spectra in the 400 nm to 480 nm wavelength range. Red wines, on the other hand, exhibit an absorption maximum at 520 nm, the absorption of red, representing the absorption of anthocyanins and their flavylium combinations, and a trough at 420 nm (the absorption of yellow representing the absorption of tannins and flavonols).

The real interest at the time was to try to detect possible adulterations, and comparisons were made between wine
musts and synthetic dye dilutions. They found that they could also detect coupage, and additions to deliberate increase the pH. It was only in 1958 that the absorption at 520 nm and 420 nm was offered as a definition of the hue (colour or "tint") of a red wine (this rapid check is still in use). So three absorption maxima were used, A280 (280 nm), A420 (420 nm), and A520 (520 nm). A520 decreased and A420 increased when dealing with aged wines, more than 10 years old (i.e. a shift to red-orange hues). So at the time A420 + A520 was proposed as a satisfactory expression of colour intensity for rosé and red wines. It was in 1980 that for Rioja wines A520 was said to represent anthocyanin and A420 the absorption due to tannins and flavonols. In 1983 it was shown for Rioja grapes and musts that there was a relationship between colour intensity and pH, refractive index, polyphenol oxidase activity, and potassium and tartaric acid content. In 1985 it was understood that polymerisation and condensation of anthocyanins and polyphenols, during the ageing process of wines, caused a decrease in colour intensity.

In 1984 a certain Y.Glories observed that in
colour evaluations, distinctness between young and aged wines was necessary. For young wines (less than a year old), if only A420 and A520 were considered, they were not sufficient. Consideration of the blue absorption component (A620), which was attributed to quinonic forms of free and combined anthocyanins was proposed. This novel component is very important in wines with a pH near 4. He went on to propose a so-called "Modified Colour Intensify" test as the sum of the three absorbances, A420 + A520 + A620, and noted that wines appear more saturated in colour as the blue component A620 increases.

So finally we can now turn our attention to the meaning of "
minimum colour intensity for red wines (A420 + A520 + A620)". It refers to a specific analysis method for characterising the chromatic characteristics of a wine using the terms luminosity and chromaticity. This is the terminology used by the OIV with the Method OIV-MA-AS2-07B. Brightness is the subjective impression of the measured luminance, and in wine corresponds to transmittance, i.e. the amount of light that is transmitted, which varies inversely with the colour intensity of the wine. Chromaticity corresponds to the dominant wavelength (which characterises the hue, tint or shade) and to the purity (clarity may be obtained by centrifugation). In the OIV method, "for the sake of convenience", they prefer to use "intensity of colour" and "shade" for both red and rosé wines.

So we now know that the
spectrum of red wine has a maximum at 520 nm, due to anthocyanins and their flavylium combinations, and a minimum in the region of 420 nm. Colour intensity and hue often only take into account the contributions at 520 nm and 420 nm, but this does not truly reflect the overall visual perception of a wine colour. The current approach to colour analysis in winemaking requires optical density measurements at 420 and 520 nm, with an additional measurement at 620 nm to include the blue component in young red wines. This is the so called the Glories method, and the measurement at 620 nm is an obligation for Rioja wines. These measurements are used to calculate the values ​​employed to describe wine colour.

The OIV method defines wine
colour intensity (I) is an amount of colour, represented by I = A420 + A520 + A620 (the sum of the absorbencies of optical densities for a 1 cm optical path), which can vary greatly with different types of wine. It is this value "I" that is used to define a "minimum colour intensity" for Rioja red wines at 3.5 and 4 respectively with and without malolactic fermentation.

The OIV method also defines wine
shade (N for hue, tint or shade) indicates the development of a colour towards orange, with N = A420/A520. Young wines have a N-value on the order of 0.5–0.7 which increases throughout ageing, reaching an upper limit of around 1.2–1.3.

Whilst not specific to the OIV method, it is possible to define chromatic structure (
chromaticity), as the contribution (in percentage) for each of the three components of the total colour. So A420(%) = A420/I x 100, and etc. for the other two optical density measurements A520(%) and A620(%).

It is also possible to define the brilliance (
brightness) of red wines (dA) as being associated with the shape of the spectrum. When the wine is bright red, the maximum spectrum at 520 nm is narrow and well defined. On the other hand, the maximum of the spectrum is relatively broad and flattened when wine is deep red or brick red. This feature can be presented as follows:

dA[%] = (1 − (A420 + A620)/(2 times A520)) x 100


Expected results of dA are between 40% and 60% in young wines, with higher values indicating a dominance of red, which we might perceive as a bright red.

It is possible to go one step further and analyse the colour in terms
CIE L*a*b*, where L is perceived luminosity (lightness, with 0 for black and 100 for pure white), and a* and b* are for the unique colours of human vision, a* for red-green and b* for yellow-blue. This application note first presented the spectra for 7 different wines. The colour intensity for the 5 red wines varied between 0.989 and 2.133, and the colour hue/shade varied between 0.806 and 0.939, without there being an obvious correlation between intensity and shade.

Absorbance Spectra of Wine Samples

The expected difference between red and white wine is seen clearly in the range between 400 and 650 nm, where red wine samples exhibit an absorbance peak due to absorption by anthocyanin that is absent in the white wines. This peak in the red wine samples may be used in separate methods to determine the anthocyanin content of the wine sample. Below we have the transmittance spectrum of wine sample 3 as compared to a deionised water sample.

Transmittance Spectra of Wine

We can now go one step further and obtain figures for the luminosity, red-green and yellow-blue colours. Luminosity varied between 56.392 and 75.233 for there'd wines, and between 99.258 and 100.185 for the white wines. As expected a* for the red wines varied between +23.064 and +36.660 (+ figures towards red), and the white wines between -0.099 and -0.144 (- figures towards green). For b* the red wines varied between +9.695 and +27.775 and for white wines between +0.819 and +1.621 (+ figures towards yellow, - figures towards blue). It is possible to calculate the square root of the additions of the squares of L, a* and b*, which is often used as a pass/fail for a sample compared to an established standard. For the 5 red wines the so-called ∆ varied between 37.873 and 63.394, and the two white wine samples between 1.037 and 1.842.

Analytic characteristics - sulphur dioxide


The fourth analytic characteristic is sulphur dioxide content, which may not exceed a certain maximum limit of total sulphur dioxide (expressed in milligrams per litre) for wines that are ready to drink. This means that for red wines with less than 5 grams of sugar per litre, the total sulphur dioxide must not exceed 140 mg/l, and for red wines with 5 or more grams of sugar per litre it may not exceed 180 mg/l. In addition, once the fermentation process is over for a dry red wine, the total sulphur dioxide must not exceed 100 mg/l.

Sulphur dioxide and its salts have been added during winemaking since the 17th century, and they remain an essential winemaking additive. No one other additive has the same dual properties of anti-oxidation and preservation. The antioxidant effect prevents the alteration of natural aromas of the grapes and wine due to the contact with oxygen. And the preservative effect helps inhibiting the development of ‘undesirable bacteria’ in the wine. And sulphur dioxide is also used to disinfect barrels.
Sulphur dioxide and its sulphate salts can cause an adverse reaction, but they are authorised food additive. The reality is that alcoholic drinks represented about ¾ of total adult exposure, and secondary sugar in jams and confectionary make up the rest.
Approximately 10-50 mg/l of
sulphur dioxide is formed by the yeast during alcoholic fermentation, and an additional 20-200 mg/l may be added during the winemaking process. So, irrespective of the amount of sulphur dioxide added, a small amount will always be measured. In most wine consuming countries, wines containing sulphites greater than 10 mg/l must include a statement on the label. Test is 2021 showed that 92 mg/l was the mean concentration for sulphur dioxide in Spanish wines, as compared to 89 mg/l for Italy and 58 mg/l for France.
The
EU (2019) has fixed a permitted maximum of 150 mg/l for red wines with less than 5 g/l sugar, and 200 mg/l for red wines with more 5 g/l sugar, but Rioja wines has set itself lower permitted maximums of 140 mg/l and 180 mg/l respectively. These limits are well below those set in the US, New Zealand, and Australia, but are similar to those set in South Africa and Argentina. The reality is that sulphates appear to be important in a wines chemical profile, and removing them would modify the organoleptic characteristics of the wine. For example, the Australian Wine Research Institute has noted that insufficient sulphur dioxide at bottling can provoke sensory deterioration, premature oxidation, microbial spoilage and high concentrations of volatile acidity.

Firstly
sulphur dioxide can be found in several different forms in must or wine. One method is to use direct titration with iodine to determine the free sulphur dioxide. The combined sulphur dioxide is subsequently determined by iodometric titration after alkaline hydrolysis. When added to the free sulphur dioxide, it gives the total sulphur dioxide. Another method is to sparge the sulphur dioxide from an acidified wine sample in an air stream, and trap it in a solution of hydrogen peroxide which oxidises the sulphur dioxide to sulphuric acid. The sulphuric acid formed is then titrated with standardised sodium hydroxide, and the amount used is proportional to the amount of sulphur dioxide in the wine.

The
OIV measurement technique is Method OIV-MA-F1-07, but the best description comes from three AWRI (Australian Wine Research Institute) video's on sulphur dioxide measurements, namely Part 1. Measurement procedures, Part 2. Quality assurance tests, and Part 3. Troubleshooting.

Analytic characteristics - reducing sugars


The fifth analytic characteristic is residual reducing sugars, which may not exceed 4 g/l. There is an exception for medium dry red wines obtained either by stopping the fermentation before its conclusion, or by sweetening dry red wines.

The sugars present in
wine grapes and wine differ in their fermentability, sweetness level and the way they can be measured.

Sugar is naturally present in grapes.
Glucose and fructose are by far the most abundant, and both are fermentable (i.e. consumed by yeast). Sucrose is just one molecule of glucose joined with one molecule of fructose, however sucrose is not a reducing sugar. Pentose is another reducing sugar, but it is non-fermentable, and does not contribute much to the perceived sweetness. Reducing sugars are sugars in juice and wine that can reduce other compounds. Their reducing ability make them measurable, but the simplest measurement method will also include other reducing compounds (such as phenolics), and does not distinguish between fermentable and non-fermentable reducing sugars. You can break down sucrose into its components, and the measurement would then give total sugar.

Residual sugar typically refers to the sugar remaining after fermentation stops, or is stopped, but it can also result from the addition of unfermented must or ordinary table sugar (sucrose). Even among the driest wines, it is rare to find wines with a level of less than 1 g/l. By contrast, any wine with over 45 g/l would be considered sweet, and for example, Château d'Yquem contains between 100 g/l and 150 g/l of residual sugar. How sweet a wine will taste is also controlled by factors such as the acidity and alcohol levels, the amount of tannin present, and whether the wine is sparkling or not. So a sweet wine can actually taste dry due to the high level of acidity, and a dry wine can taste sweet if the alcohol level is high.

There is quite a lot of information available on rapid tests for the approximate
sugar content of wines using one or other type of test pills (many sources appear out of date). However I prefer to align my summary description with the methods of analysis recommended by the OIV.

The
Abbe refractometer measures the index of refraction, is available as a handheld device, and delivers actual sugar content (g/l) for grape juice and grape must. These devices need only a few drops of grape juice or grape must, they calibrate themselves automatically, and compensate for temperature. For must sugar content they are accurate to +/-1 g/l, and they can also be set to measure degree Oechsle. The same devices also measure specific gravity, as well as potential alcohol of grape must and actual alcohol percent by volume of finished wine via distillation.

The
OIV Method OIV-MA-AS311-06 determines polyols derived from sugars and residual sugars found in dry wines, and the technique is high-performance liquid chromatography (HPLC). Sugar alcohols are low molecular weight polyols, and HPLC can be used for the direct quantification of sugars in musts and wines up to 20 g/l and, after dilution, for higher concentrations. Sugars and glycerol are separated by HPLC and detected by a refractometer. Glycerol is an important fermentation by-product (after alcohol and carbon dioxide), and although colourless and odourless, it contributed positively to a wine's texture, body and mouthfeel. This technique is particularly valuable if the equipment and skilled personnel are already available.

Some sources mention the Lane-Eynon method and the Rebelein method, both of which rely on reacting the sugars with
alkaline cupric tartrate and then titrating to determine the excess copper ions. In both cases, red wines must be decolourised, and both of these techniques measure all of the sugars in the wine (i.e. all reducing sugars including pentose) and give higher results than tests that determine just the concentration of glucose and fructose.

There is also mention of the conversion of
glucose and fructose by specific enzymes which can be monitored directly by using a ultraviolet spectrophotometer to measure the absorbance (340 nm) resulting from the generation of a by-product of the reaction (NADPH). This test is quite straightforward and requires only sample dilution, but of course you need the equipment and skilled staff.

Analytic characteristics - acidity


The sixth analytic characteristic is the total acidity of wine, which may not be less than 3.5 g/l of tartaric acid.

The main organic acids in grape juice and wine are tartaric, malic, citric, succinic, and lactic, along with some minor concentrations of other compounds, and they directly affect wine pH. Tartaric, malic and citric are molecules that come from the grape, whilst succinic and lactic acids have a microbiological origin, i.e. produced during fermentation. The first three acids depend upon the grape variety, harvest date, latitude and climatic conditions, seasonal weather conditions, and vineyard management practices. For example, tartaric acid is an organic acid that occurs naturally in many fruits, most notably in wine grapes. Tartaric and malic acid account for over 90% of the total acids present, and tartaric acid is the strongest organic acid in must and wine. Its salt, potassium bitartrate, commonly known as "cream of tartar", develops naturally in the process of fermentation, and can appear as an insoluble deposit in wines.

Acidity is highest in
wine grapes just before the start of veraison, which ushers in the ripening period of the annual cycle of grape vines. As the grapes ripen, their sugar levels increase and their acidity levels decrease. Through the process of respiration, malic acid is metabolised by the grapevine. Grapes from cooler climate wine regions generally have higher levels of acidity due to the slower ripening process. The level of acidity still present in the grape is an important consideration for winemakers in deciding when to begin harvest.

In the
winemaking process, acids aid in enhancing the effectiveness of sulphur dioxide to protect the wines from spoilage and can also protect the wine from bacteria due to the inability of most bacteria to survive in low pH solutions. In red wines, acidity helps preserve and stabilise the colour of the wine. The pH measurement is used in the vineyard to assess the ripening pre-harvest, to calculate sulphur dioxide requirements after fermentation, and to assess oxidation risk because high pH wines are generally more prone to oxidation. Titratable acidity is applied to the sensory perception of a wine’s acidity, i.e. its tartness, sourness, crispness. While pH and titratable acidity are related, pH is a measurement of the likelihood and speed of occurrence of pH dependent reactions, while TA is the best estimate of a wines perceived acidity.

Winemakers will sometimes add acids to the wine (acidification) to make the wine more acidic, most commonly in warm climate regions where grapes are often harvested at advanced stages of ripeness with high levels of sugars, but very low levels of acid. Tartaric acid is most often added, but winemakers will sometimes add citric or malic acid. Acids can be added either before or after primary fermentation, or later during blending or ageing, but the increased acidity will become more noticeable.
However, even without specific acidification or deacidification, the acidic fraction of wines will fluctuate, e.g. one reason is that total acidity and organic acid composition changes after
alcoholic fermentation, i.e. production of succinic and lactic acids. Because of this it is generally recommended to perform acidification or deacidification on the wines rather than the musts.

In the winery titratable acidity is the best practical expression of the organic acid concentration within must or wine. As mentioned above the actual acid composition and concentration within the must or wine is influenced by many local factors and their presence contributes to both a wine’s flavour and to its stability, colour, and pH. For this reason when a viniculturist knows the exact organic acid makeup of a wine or must they can make educated vinification decisions to optimise flavour and stability. During the berry’s progression to veraison, acids accumulate within the fruit. At veraison, the total acidity in the fruit decreases, primarily due to the reduction of malic acid. At harvest, the fruit usually contains more tartaric acid than malic acid, the exact concentrations and ratios to one another being cultivar specific and harvest date dependent. Grapes are one of the rare fruits that contain tartaric acid, and its presence in its salt form is an important constituent, affecting pH and the cold stability of the wine.

It is a mistake to think of titratable acidity and pH as directly correlated as acidity indicators, they are not. The measurement of pH is the number of hydrogen ions in a solution using a logarithmic scale, with a lower number denoting a higher concentration of ions. This means that the difference between a wine with a pH of 4.0 and one with a pH of 3.0 is that the wine with the pH of 3.0 has 10 times as hydrogen ions as the pH 4.0 wine. The measurement of acidic content is the acid’s potential to liberate hydrogen ions as it dissociates. While acid content affects pH, it is not directly predictive of pH (or vice versa). This non-direct correlation is partially due to pH “buffering” caused by a number of compounds in wines, such as sugars, acids, and phenolic compounds. Buffering occurs because these compounds exist in equilibrium between their acid and conjugate base forms, and the ratio of the two forms to one another must be significantly shifted before a noticeable pH change can occur. Just as pH calibration buffer solutions effectively calibrate pH equipment due to their reliable stability, the addition of a given amount of acid to a wine may not reduce the pH as expected due to the wine’s buffering capacity to maintain a stable pH.

In taking pH and titratable acidity measurement one is also measuring two different chemical attributes of the wine or must. With a pH meter one is measuring an electrical gradient created by the solution inside the cell of the pH probe and the wine. With titratable acidity one is measuring the amount of strong base that it takes to raise the solution to pH 8.2 accounting for both acid content and buffering capacity. As we can see in the regulatory definition the titratable acidity is quantified in terms of g/l of tartaric acid, as if it were a quantification of only tartaric acid, whilst in fact, the number represents the concentration of all titratable acids, e.g. including malic, citric, lactic, succinic acids.

To get a better idea of role of titratable acidity and pH through the entire wine making process, check out "
Managing acidity in grapevines and wines", and the eBook "Measuring TA in Wine".

In different parts of the Rioja regulatory texts "total acidity" and "titratable acidity" are mentioned, and "real acidity" is also used as meaning a wines
pH. However, as suggested above they don't mean exactly the same thing. Total acidity is the proton equivalence (i.e. hydrogen ions) of the amount of organic acid anions present in a wine. It is the number of hydrogen ions that the organic acids (lactic, succinic, citric, acetic, and sulfurous acids) would contain if they were totally undissociated (i.e. not disassociated into oppositely charged ions). It is calculated by measuring the acid anion concentration (by spectrometry or chromatography), expressing them as molar quantities (number of molecules per volume), and then multiplying by the number of hydrogen ions that would result from complete dissociation. Titratable acidity is the number of hydrogen ions recovered during a practical titration with a strong base to a specified endpoint. It can also be expressed as a molar quantity. Many people use titratable acidity and total acidity as synonyms, but they are not. The titratable acidity is always less than the total acidity, because not all of the hydrogen ions expected from the acids are found during the determination of titratable acidity. However, titratable acidity is easier to measure. And pH is the logarithm of the concentration of free hydrogen ions, expressed with a positive sign.

The
OIV defines the total acidity of a wine simply as the "sum of its titratable acidities, when it is titrated to pH 7 against a standard alkaline solution" (excluding carbon dioxide). So in their definition total acidity reflects the total amount of hydrogen ions releasable by organic acids. The easiest analysis technique is just measuring the sum of the titratable acidities when it is titrated to pH 7 against a standard alkaline solution. You need to eliminate carbon dioxide and calibrate a pH meter. You then introduce a small quality of wine or must, and add sodium hydroxide solution until the pH equals 7 at 20°C. "n" in ml is the volume of sodium hydroxide added, and the total tartaric acid per litre is equal to 0.75 time "n". The OIV provides Method OIV-MA-AS313-01, which describes how to perform these measurements, however automatic titrators are commercial available. Below we have an ideal automatic titrator, which also doubles as an accurate pH metre. As we can see it's a reasonably simple piece of laboratory equipment, and the procedures are relatively easy.

Features of an Ideal Titrator


Analytic characteristics - pH


The seventh analytic characteristic is pH, which may not be less than 2.8 nor more than 3.3.

From a theoretical point of view, pH is proportional to the reciprocal of the relative activity of hydrogen ions in solution, and in wine the pH is often described as its "real acidity", because its connected to wine freshness and the sensory perception of sourness.

The control of acidic fraction and
pH might be seen as less problematic for red winemaking, simply because red wines are generally less acidic with respect to white wines, and they also undergo malolactic fermentation during ageing. But getting the measurements wrong can compromise the quality of a wine, and in particular now that consumers are tending towards "sweet" tannins and looking for greater colour stability, i.e. an increase in the pH of red wines as compared to some decades ago. Microbiological and physiochemical stability is connected to the pH, as is the malolactic fermentation. A change in pH can affect the natural selection of micro-organisms during winemaking, and its directly involved in the definition of the equilibrium of sulphur dioxide in the wine (affecting the amount of free and molecular sulphur dioxide available).

Interestingly, the determination of
pH is one of the simplest analytical parameters used in wine quality control, yet one of the most important. Different typologies of combined glass/calomel electrodes are available commercially, and the OIV has established specific recommendations for the electrodes and calibration buffers (Method OIV-MA-AS313-15).

Rioja wine classification - sensory characteristics


The Rioja rules and regulations state…

Sensory Characteristics involve the
organoleptic certification of characteristics such as the typicity, colour, limpidity (clear, transparent, bright), smell (aroma), taste and quality of the wine, taking into account the moment of the production process at which the sample was taken.

The Rioja classification documents indicate the following sensory characteristics for each of its wine types, which I presume are targets to be met by winemakers:-

Young Red Wine
Eye: Purple with bluish hues.
Nose: Intense varietal fruit with floral sensations.
Mouth: Flavour-packed with balanced acidity, alcohol and tannins.

Crianza Red Wine
Eye: Garnet and cherry red.
Nose: Harmony between fruit and toasty notes from the oak.
Mouth: Good body with smooth, tasty tannins.

Reserva Red Wine
Eye: Dark-cherry red with a ruby trim.
Nose: Complex, with well-integrated ripe fruit and spicy aromas (vanilla, roasted coffee, tobacco).
Mouth: Good structure and flavours in harmony. Smooth and velvety.

Gran Reserva Red Wine
Eye: Ruby-red with brick hues.
Nose: Very complex, intense aromas, with spicy notes (tobacco, roasted coffee, nuts, cloves, walnuts, cedar).
Mouth: Smooth, fine and elegant, with high persistence.


In order to really appreciate what are these "sensory characteristics", we need to look more carefully on what those characteristics really mean. Under sensory characteristics there is mention of "Eye" with
colour and limpidity (clear, transparent, bright), "Nose" clearly refers to smell or aroma, and "Mouth" must mean taste and more generally mouthfeel.

Wine psychological


Before we turn to sensory characteristics, it's worth looking at
the psychological basis of wine consumption. Traditionally and understandably, research in the world of wine has tended to focus on oenology, viticulture, and wine sensory analysis, but until recently far less on what might be called "wine psychology". But increasingly research has shown that cognitive and perceptual factors (such as learning, sensation, attention, and memory), influence the wine-drinking experience, both with wine experts and regular consumers alike. The perception of wine itself and the wine-tasting experience more generally have been shown to be influenced by everything from the weight of the wine bottle through to the sound made by its closure and the glass from which it is drunk, to the wine’s visual appearance and the multi-sensory environment/atmosphere in which it happens to be consumed. There is undoubtedly a great deal of psychology in the world of wine appreciation not to mention wine choice, however neuro-imaging research has looked at how the brain response changes as a result of increasing wine expertise, and even the effects of pricing/branding information on the brain’s response to wine. Of all the food and beverage products that could potentially be studied, it is wine that has received by far the most research interest over the last half century or so. In fact, no matter whether one is talking about the impact of colour, glassware, packaging, branding, label design, closure type, pricing, or perceptual expertise, there is just so much more research in the world of wine than in any of the world’s other more popular drinks such as, for example, coffee, tea, beer, or water.

The context, or atmosphere, in which a wine happens to be consumed also turns out to have a profound effect on the tasting experience, e.g. the
Provencal rosé paradox is where the wine tastes delightful while on holiday, but often tastes very different, and much less enjoyable, back at home.

The fact that
colour influences aroma, taste, and flavour has long been known in the world of wine. For example, there was a famous tasting of white wine, rosé wine and a deliberately mis-colouring white wine made to look like a rosé. The group consisted of 22 beginners, 62 "who knew what they liked", and 79 experts with 5+ years formal wine tasting experience. Overall, the fake rosé wine was liked less than either of the authentic wines, and the participants found it more difficult to describe the fake than the authentic rosé wine. However, they nevertheless used the red fruit terms to describe fake rosé's aroma and flavour. And the experienced tasters appeared to be more influenced by colour than the non-expert participants, presumably because the subtle gradations of colour in wine have more meaning, and hence set more specific flavour expectations, for experts than for the beginners. It must be said that wine experts can correctly group red and white wines on the basis of their aroma when served in black tasting glasses, but they struggle when it comes to categorising rosé wines correctly.

The
clarity/limpidity is another important aspect of a wine's visual appearance, even if the intensity of a wine's appearance is often described in terms of simple adjectives such as pale, light, and weak at one end of the spectrum through to deep, dark, and intense at the other. To the knowledgeable wine taster, intensity can indicate climatic conditions, with warmer years and warmer regions producing wines with deeper intensity. White wines pick up a deeper colour as they age, whereas red wines tend to go paler. Thicker-skinned red grapes tend to produce wines with a deeper colour, whereas mature reds tend to take on garnet and tawny hues. Youthful red wines often have a bright slightly-blueish tint. However, the warning signs are there since it is also known that everything from the colour of the wine label, through to the colour of the wine glass itself, to even the colour of the environment in which a wine is evaluated has now been shown to bias people's wine expectations/judgements.

Studies have demonstrated that even wine experts, when
tasting blind, are unable to correctly judge many of the attributes of wines that they actually describe in their writings. In one trial they were unable to correctly judge the percentage of white grapes in sparkling wines, nor correlate their hedonic ratings with the price of the sparkling wines, despite the fact that the wines varied from around £18 to an "eye-watering" £400 a bottle for the most expensive. Other blind trials have shown that experts had difficulties differentiating single varietal wines from blended wines, and even single malt whiskies from their blended counterparts. The reality appears to be that wine tasting is far more complex than initially imagined. Experts are expert because they perceive and integrate a whole range of sensory inputs, but are challenged to discriminate wines blind on the basis of just their age, or quality, or price. However there is evidence that experts are most able to name and categorise wine-relevant aromas. It would appear that experts tend to learn in situations where only a single specific attribute is varied, but blind trails are often designed to vary a number of attributes simultaneously.

This may appear rather academic, but in fact it strongly impacts
wine marketing. There was a wonderful study in 1990's showing that shoppers in a UK supermarket bought significantly more French (than German) wine when French music was played, whereas they purchased more German wine on those days on which German music was played. Yet very few shoppers thought that the music playing in the background had influenced their choice. Elsewhere, it has been demonstrated that playing classical music rather than top-40 hits resulted in people spending significantly more money in a North American wine store. This bias has since been replicated in the restaurant/cafeteria context with people’s selection of food.

At a far more practical level, it has been shown that shoppers often have difficulties finding the bottle they want, and they often don't ask for help because they can't remember/pronounce the name of the wine they are looking for, i.e. try pronouncing Eitelsbacher Karthäuserhofberg Riesling Kabinett, Piesporter Goldtröpfchen, or Cserszegi Fuszeres. Some shoppers expect a more complex tasting experience from a
wine with a complex name. But we must not forget that luxury brands have known for some time the power of "sound symbolism", i.e. high-end fashion magazines are full of easy to remember yet evocative brand names. If it's easy to pronounce, it's easy to remember. We no longer live in a world where a producer just sticks a label on his bottles. Chardonnay's aroma characteristics, namely buttery, citrus, floral, smoky, and vegetable, are often echoed with simple labels using red, brown, yellow, and green (in particular yellow). Red and black wine labels for red wine are most likely to create tangy flavour expectations, while red and orange are most associated with fruity and flowery flavours instead. A correlation has also been demonstrated between the weight of the wine bottle and the price. Consumer were willing to pay an average of £1 more for each 8 grams extra weight of glass. The presence of additional weight may also help to explain why so many people prefer drinks from a bottle rather than from a can. Trails have shown that people associated better quality wine with the action and sound of a cork-stoppered wine bottle being opened, as opposed to opening of a screw-top bottle.

In the world there are more than a million wine producers, all producing a new wine every year, so it's not surprising that people can be a bit overwhelmed and confused. This obviously makes the wine-taster’s job much harder on blind tasting, at least as far as identifying specific wines, and when it comes to the regular consumer purchasing wine in the store, the marketers have to fight to stand out from the
constantly changing competition on the wine shelf.

Whenever we drink, there is always a receptacle, be it a glass, beaker, mug, bottle, or can. At least 20 studies have been published assessing the impact of the shape/size of
the wine glass on people’s rating of the aroma/bouquet and taste/flavour of wine. The research clearly shows that if the taster does not know which wine glass they are evaluating a wine in/from, either because they have been blindfolded while the glassware is agitated under the taster’s nose, or because the glass in which the taster evaluates the wine is different from the glass in which the wine has been allowed to breathe, the glassware seems to make little difference to the taster’s experience. However, as soon as the latter become aware of the nature of the glass from which they are tasting, the glassware can suddenly make a huge difference to the tasting experience. Yet on the other hand it looks as if the specific shape of the glass, or the headspace above the wine, makes no noticeable difference to the tasting experience.

One of the most extensive public wine tasting (almost 3,000 people) involved a single 100-ml glass of
Campo Viejo Reserva 2008 Rioja red wine under four different ambient conditions, involving regular white lighting followed by either red or green lighting. Both of the latter two coloured-lighting conditions were then presented together with putatively "sweet" or "sour" music. The participants were given a scorecard on which they rated on line scales “How fruity vs. fresh does the wine taste?”, “How intense the flavour?” and “How much do you like the wine?” The results revealed that the wine was rated as tasting significantly fruitier under red than under green lighting, and with putatively sweet rather than with sour background music. Others have reported that changing the visual atmospherics in a room (introducing flowers, pictures, and coloured lighting) had no effect on 105 wine consumers’ ratings of a red wine. We all know that if something induces a positive mood or emotion then its likely to impact on the way we taste wine (and food, etc.). It's also worth remembering the fact that the consumption of significant amounts of alcohol has been reported to give rise to a change in perception of those of the opposite sex. And it equally important to remember that alcohol can sometimes dramatically affect our decision making.

As a counter-point to the above have a read of "
Wine-tasting: it's junk science".

What are sensory characteristics?


Sensory evaluation or
sensory analysis is a scientific discipline used to evoke, measure, analyse, and interpret reactions to the characteristics of foods and materials as they are perceived by the senses of sight, smell, taste, touch, and hearing. Sensory evaluation is used throughout the winemaking process to aid in decision making. To ensure that production decisions are made, based on an understanding of true sensory differences, it is vital that regular assessments be performed. Without the proper sensory evaluation techniques, it is difficult to interpret sensory responses and make logical and sound decisions.

In looking at the quality of Rioja wines, we can see reference to a variety of sensory characteristics, i.e.
typicity, colour, limpidity (clear, transparent, bright), smell (aroma or odour), and taste. The descriptions outlined in the Rioja rules and regulations concern the final product, but in fact sensory characteristics are tested throughout the production process, and concern not just what makes a high quality final product, but also how to manage the winemaking process after each harvest, and above all, how to rapidly detect faults and avoid the risk of spoilage.

We will try to understand some of the descriptive sensory methods used for the
sensory analysis of wine.

In very simple terms,
sensory analysis can involve both analytical testing (e.g. discrimination testing, quantitive descriptive analysis), and affective or subjective testing (e.g. rating which wine might have the more fruity aroma, and which might be the most appreciated, and do people "like" or "dislike" something).

Commonly used
affective methods include a paired preference test, a preference ranking test, and the hedonic test method. The test method has to be simple and easy to understand, so the consumers (or experts) making up a tasting panel will know how to respond. Once a significant difference has been established between two wines (using a discrimination test), a separate preference test can be performed. For example, this is useful in determining which wine blend or which yeast fermentation is preferred (presuming that they can discriminate between the two). In determining preference, it is also important for the tasters to consider the desired wine style required before tasting the wine. The preference decision is not a personal preference, but a preference for the wine which best suits the desired wine style. If more than two samples are evaluated, a preference ranking test can be used. Normally three to five samples are the most that can be efficiently ranked by a consumer. A hedonic scale is used to determine the degree of acceptability of one or more samples. It generally involves a category-type scale with categories ranging from "dislike extremely" to "like extremely", with a neutral midpoint (neither like nor dislike) included. One variation on the discrimination test is the "triangle test" where three samples are used to determine if a difference exists between two wine samples, i.e. two samples are in fact identical and the panelists are asked to pick the odd-one-out. A slight variation on the "triangle test" is the "duo-trio test" involving a reference wine and two test wines. However, one of the two samples is the same as the reference wine, and the tasters are asked to identify the identical sample. The "pair comparison test" is a variation of the significant difference (discrimination test) in the sense that the question might be "which sample is more acidic"? Another variation is the "same/different test" where tasters are asked to identify whether they think the two wine samples are the same or different.

Many researchers view
quantitive descriptive analysis as the best approach because it is both empirical and yet provides precise measurements and permits a detailed analysis. In quantitative research design, the researcher will count, classify, and build statistical models to explain what is observed. The idea is to use a small number of people who are both experienced and sensitivity to product differences. They may use a standardised vocabulary or they may develop their own terms for the sensory attributes. The aim is a degree of objective facts, but they are more likely to use "bitterness" rather than "alkalinity", Here the aim is to go well beyond simplistic descriptions such as "like", "dislike", "better", "good", or "bad". The questions could simply be about product differences (discrimination testing) or they could be about characteristics of different products (descriptive analysis). The aim is not an absolute assessments, but a relative assessments of the characteristics of a series of wine samples.

What are the basics that can be assessed using
sensory analysis? The first point to think about is how wine samples are presented to a tasting panel. For example, wineries generally serve all their whites at one temperature, and all the reds at another. However, this may not be optimal, because cooling tends to reduce the sense of sweetness of sugars and the bitterness of alkaloids. And on the other hand, cooling tends to increases the sense of acidity and the bitterness and astringency of tannins.

Sugar concentrations above 0.2% are generally required for a wine to exhibit perceptible sweetness. However when sweetness is detected in dry wines, it is often due to the presence of a noticeable fruity fragrance. Association between fruity odours and sweetness has trained us to instinctively affiliate the presence of fruity odours with sweetness, even in its absence. Sugars begin to have a pronounced influence on the perception of sweetness at or above a concentration of 0.5%. The influence of aromatics on the perception of the sweetness of sugar can be very important, and the fragrance may not only evoke the perception of sweetness, but also increase the perceived intensity of sweetness.

Body is often mentioned in the overall assessment of the quality of a wine, despite the fact that its precise origin remains unclear. Many people correlate body with flavour and/or perceived viscosity. In sweet wines, body is often viewed as being roughly correlated with sugar content. In dry wines, it has often been associated with alcohol content. Features such as a wine’s fragrance can influence the perception of body and, conversely, increasing the sugar content can increase the perception of fragrance.

Ethanol slightly enhances the sweetness of sugars, while reducing the perception of acidity. At high concentrations (above 14%), alcohol increasingly generates a burning sensation, and may contribute to the feeling of weight or body, especially in dry wines.

Acidity diminishes the perceived sweetness. Of the common acids found in wine, malic acid is the most sour tasting, whereas lactic acid is generally considered the least sour. The perceived intensity of a mixture generally reflects the intensity of the dominant component, not a summation of their individual effects. pH also impacts taste perception, both directly by influencing the ionisation of salts and acids, and indirectly by affecting the shape and biological activity of proteins. Structural modification of receptor proteins on tastebuds can significantly affect taste responsiveness. The use of oral hygiene products can impact tastebuds, making most wines taste much more acidic. The so-called "Orange Juice Effect" is the result of sodium lauryl sulfate (or sodium dodecyl sulfate, two names for a common toothpaste ingredient) that can react with tastebuds. This is a primary reason why sensory evaluations are generally not conducted too early in the morning.

Salt of some cheeses can suppress the bitterness of red wines. In some cases the duration and maximum perceived intensity can be affected.

Astringency (puckeriness) is primarily induced by flavonoid tannins that come from grape seeds and skins. Anthocyanins can enhance the perceived astringency of tannins, but do not contribute to wine bitterness. Both astringency and bitterness perceptions develop comparatively slowly and possess lingering aftertastes. Astringency may partially mask bitterness, and is more often confused with bitterness than the inverse. Astringency is thought to result from the binding and precipitation of proline-rich salivary proteins and glycoproteins with phenolic compounds, and is one of the slowest in-mouth sensations to develop. Depending on the concentration and types of tannins, astringency can take up to 15 seconds before reaching maximal intensity. The decline in perceived intensity occurs even more slowly. The intensity and duration of an astringent response often increases with repeat sampling. This phenomenon is less likely to occur when the wine is consumed with food, owing to reactions between tannins and proteins in the food, as well as due to dilution.

Mouthfeel is a generalised term used to describe multiple sensations including astringency, viscosity/body, a burning sensation, prickling from carbon dioxide, etc. The combination of these sensations with those from the nose produces the perception of flavour. Unlike gustatory (taste) and olfactory (smell, aroma or odour) sensations, mouthfeel activation occurs slowly, and adaptation is also slow or may not develop. The latter is particularly evident in the increased intensity of astringent sensations on repeated exposure to red wines. This is why the use of palate cleansers during tasting is recommended. Taste- and mouthfeel-components can affect taste, for example:-

Professionals in the field always use plain bread and wash it down with water to cleanse their palettes. It should be a small amount of bread or crackers. After eating the piece of bread, it should be washed down with plain, unflavoured water (not carbonated or spring water).

There are guidelines on performing sensory analysis provided by the
Organisation Internationale de la Vigne et du Vin, which in addition to providing advice on the tasting room and sample preparation, also mentions the use of special tasting glasses (established in ISO 3591:1977). This glass must be made of colourless, transparent crystal glass containing about 9% lead (so lower than usual), and have the dimensions indicated below.

ISO Wine Tasting Glass

The ISO tulip-shaped tasting glass with a volume of 215 ml is a bit different from the "classical" wine glass which has a volume of 230 ml. The ISO glass has a rounder bowl and narrow sides making it easier to swirl around the wine without any spillage. Being narrower is said to help contain the aromas, but the shape is also designed to prevent a taster being influenced by the colour or transparency of the wine. There have been suggestions that a medium sized "classical" wine glass shape with a slightly larger bowl, higher walls and a medium size opening might actually perform better, particularly for fruity, spicy and nutty aromas, as well as for a sulphur defect.

As mentioned above there are International Standards (ISO) that serve as guidance for establishing sensory profiles performed by trained assessors. The sample may be almost anything, e.g. food, beverage, tobacco product, cosmetic, textile, paper, packaging, sample of air or water, etc. Profiling can be carried out in a number of ways. Over the years, a few of these have been formalised and codified as descriptive procedures by professional societies or by groups of producers and users for the aim of improving communication between themselves. And the purpose of the International Standards is to provide agreed guidelines for the overall process for establishing a sensory profile. Some applications of sensory profiling are as follows:-

  • To develop or change a product

  • To define a product, production standard, or trading standard in terms of its sensory attributes

  • To define a reference "fresh" product for shelf-life testing

  • To study and improve shelf-life of a product

  • To compare a product with a reference product or with other similar products on the market or under development

  • To map a product's perceived attributes for the purpose of relating them to factors such as instrumental, chemical or physical properties, and/or to consumer acceptability

  • To characterise by type and intensity the off-odours or off-tastes in a sample.


Many of the ISO standards concern methodologies, guidelines, and vocabularies, but there are also some very specific standards concerning tasting glasses, cork stoppers, glass containers (e.g. bottles), testing grape harvesting machinery and presses, as well as more generally topics such as odour, flavour and taste detection thresholds, and general taste sensitivity and mouthfeel.

So according to expert advice, a
sensory session should be held in the mid- to late-morning, with blind and coded samples, and involve a small number of properly trained people who are both experienced and proven to be sensitivity to product differences. Generally, for the evaluation of wines, three groups of sensory attributes should be assessed, namely the appearance, the odour and the flavour (being a complex combination of the olfactory, gustatory and trigeminal sensations perceived during tasting).

Sensory characteristics - colour


I guess
colour, as a sensory characteristic, is determined by the statements that:-
  • A young red Rioja must have a purple colour with bluish hues.

  • A Rioja crianza must have a garnet and cherry red colour.

  • A Rioja reserva must be dark-cherry red with a ruby trim.

  • A Rioja gran reserva must be ruby-red with brick hues.


Purple has often been quoted as a characteristic of very young wines with short or no ageing in oak or tanks at the winery. The purple hues can be observed only to the rim, as a purple wines look dark and generally appear nearly black to the core of the wine glass.
Garnet is often mentioned when the wine is slightly tainted by some orange hues, making it look a little bit brown.
Ruby is the most common colour mentioned for red wine, a ruby wine is a clearly-bright red wine, without any purple or orange/brown hues.
Tawny is occasionally used to describe a red colour with clear brown hues to it.

We have already encountered colour intensity as a specific analytic characteristic, and defined by the
OIV in Method OIV-MA-AS2-07B. In the description it was suggested that it is possible to go one step further and analyse the colour in terms CIE L*a*b*, and that is what the OIV does in Method OIV-MA-AS2-11 on the "Determination of chromatic characteristics according to CIBLab".

The
colour of a wine is one of the most important visual features available to us. Colour is a sensation that we perceive visually from the refraction or reflection of light on the surface of objects. Colour is light, and wine absorbs a part of the spectrum of light and reflects another part. It is the reflected part of the spectrum that reaches the eye, and provides the sensation of colour. For instance, the appearance of very dark red wines is almost entirely due to the fact that incident light is absorbed by the wine.

The description and measurement of colour is defined by something called the
CIE L*a*b* colour space, where L* is perceptual lightness, and a* and b* represent the four unique colours of human vision, namely red, green, blue, and yellow (i.e. the colour space is three-dimensional). The idea is that the colour space is perceptually uniform, which means that each numerical change corresponds to a different perceived colour. It is also both device-independent and observer-independent (i.e. based upon a "standard observer"), and covers the entire range of human colour perception, or gamut. It is based on the opponent colour model of human vision, where red and green form an opponent pair, and blue and yellow form a different opponent pair. The lightness value, L* defines black at 0 and white at 100. The a* axis is relative to the green-red opponent colours, with negative values toward green and positive values toward red. The b* axis represents the blue-yellow opponents, with negative values toward blue and positive values toward yellow. In theory the a* and b* axes are unbounded, and depending on the reference white, they can easily exceed ±150 to cover the human gamut. However, in a practical situation, such as the evaluation of wine colour, they will be bounded.

Apple 1Apple 2

Here are two apples with slightly different colours. Taking the same spot on both we can obtain L*a*b* colour space coordinates for each. For Apple 1, the coordinates are L* = 43, a* = 48, and b* = 14. The difference for Apple 2, as compared to Apple 1, is only L* = +4 (a bit lighter), a* = -3 (a bit less red), and b* = +1 (very slightly yellower).

With wine the aim is to adopt a
spectrophotometric method to measure its chromatic characteristics in a way that imitates how real people observe colour. Three attributes or specific qualities are defined, namely:-

  • Tonality is defined as "colour itself", i.e. how much of red, yellow, green and blue is in the colour as seen

  • Luminosity is defined as how much the wine is luminous

  • Chromatism is defined as the "level of colouring" or the intensity of the colour.


The
Organisation Internationale de la Vigne et du Vin defines these three attributes as "Tonality, colour itself, is the most characteristic: red, yellow, green or blue. Luminosity is the attribute of visual sensation according to which a wine appears to be more or less luminous. However, chromatism, or the level of colouring, is related to a higher or lower intensity of colour. The combination of these three concepts enables us to define the multiple shades of colour that wines present".

I'm not sure about the exact significance of "tonality" is this context, simply because in colour theory "tone" is produced either by mixing a pure colour with grey, or by both tinting and shading. Tinting is a mixture of a pure colour with white (and increases lightness), shade in a mixture with black (increasing darkness), and a tinted colour mixed with a shaded colour can produce an identical colour to a specific tone. My understanding is that a mix of red, yellow, green and blue produces a specific hue, i.e. the specific colour that the wine appears to have. The hue (colour) of a wine will often be described as being more or less colourful, intense (i.e. saturated), light (dark), or bright (dull).
My best idea for
colourfulness is when we look at the same glass of wine on a sunny day or on an overcast day. In a measurement instrument the wine will always have just one colour spectrum, but depending upon the natural illumination it will look completely different from one moment to another. Chroma is the wine colour, as defined by its spectral properties, and represents the colourfulness of an area as compared to a white area of the same brightness (so its how much the colour departs from the neutral colour). The intensity of the colour is usually called "saturation", and is the colourfulness of the wine in proportion to its brightness, i.e. how much the colour is different from white. The less the colour is free from the "whitishness" of the light coming from the area, the more it is considered colourful or "saturated". My understanding is that colourfulness, chroma, and saturation are attributes of perception and cannot be physically measured.

I guess that luminosity is the amount of light we see that has passed through, been emitted from, or was reflected by the wine. A instrument would make an objective measurement of this, whilst a person looking at the wine would use the subjective term brightness. This would be how much light appears to shine from the wine, and will normally be affected by the viewing environment.

Chromatism appears to be defined as "level of colouring" or the intensity of the colour, but I am not sure how this compares to "saturation" which is also used to define the "colourfulness" or intensity of a colour. Chromaticity exists and is specified by a combination of hue (colour) and colourfulness (which can just as easily be called saturation, chroma, purity, or intensity). Chromatism is used in the measurement procedures text, but in a graphic included in an annex the combination of chroma and hue is called chromaticity.

So whilst I am not sure how these parameters map to the traditional view of colour space, nevertheless the Organisation Internationale de la Vigne et du Vin provides a detailed procedure for their measurement.

A spectrophotometer measures the
intensity of a light beam transmitted through a sample of wine. The spectrophotometer must perform transmittance measurements at a wavelength of between 300 and 800 nm, with illuminant D65 and 10° observer cone, and have a resolution equal to, or better than, 5 nm. Visible blue to visible red covers a spectrum from about 400 nm to 700 nm.
A small but representative sample of the wine is taken (
clarified if dull), and the transmittance is measured every 5 nm across the entire spectrum from around 300 to 800 nm, with a wide viewing cone of 10°. There is usually a standard software package that calculates L*, a*, b*, and eventually C* and H*.

Colour Space for Wine

Above we can see the CIE L*a*b* colour space, where L* is usually called the "lightness" value, and is defined as black at 0 and white at 100, whereas here it is called "clarity" and is explained as being the visual sensation of luminosity. The red-green and yellow-blue components are a* and b* respectively. C* is called chroma and is defined as a vector in the (a* b*) space, and H* is defined as tone. In the official documentation the tone H* is defined as "the angle of hue", which appears to be an angle (expressed in °) between +a* and +b*. The 90° angle space between +a* and +b* covers all lighter coloured reds and some of red colours slightly tinted with blue.

Chromatic Characteristics of a Young Red Wine

Above we have an example of the measurement results as provided in the official measurement procedure (it is for a young red wine).

Franky, what we see above is a complex description, and the
OIV has done nothing to make it more understandable, nor are there any videos on the measurement procedure.

Here we mentioned the
transmittance of light through the wine sample. Light incident on a sample can be reflected, absorbed, or transmitted, and the ratio of the light transmitted through the sample to the light incident on the sample is defined as the transmittance. However, in fact, it is absorbance that is routinely quoted in spectrophotometer measurements. The reason is that absorbance is both proportional to the concentration and to the optical path length (Beer-Lambert-Bouguer Law).

If we return to an earlier graphic (repeated below) we can see an alternative way to view to view H* (which others have preferred to simply call
hue and not tone). Here we can see H* defined as the angle "T" of the straight line drawn through the minimum at A420 and the maximum at A520, i.e. T = A420/A520.

Absorption Spectra for White and Red Wines

With respect to wine ageing, red wine assumes a shift from strong red towards orange-red, due to the transition from monomeric to polymeric anthocyanins, respectively. In the spectral domain, this translates to a decrease of A520 and an increase of A420, which influences the hue accordingly.

Brightness (dA[%]) measures the clearness of the wine and is linked to the shape of the absorption spectrum, as prescribed by equation

dA[%] = (1 − (A420 + A620)/(2 times A520)) x 100


and corresponds to the A420, A520 and A620 triangle median length, as seen in the above figure. So brightness measure the contribution of red, i.e. the flavilium cations of the free and combined anthocyanins to the wine colour. Accordingly, a larger brightness value stands for a dominance of the red colour of the wine.

The "chromatic characteristics" of a wine have also be defined as its
luminosity and chromaticity. Luminosity depends on transmittance and varies inversely with the intensity of colour of the wine. Chromaticity depends on dominant wavelength (distinguishing the shade) and purity. Conventionally the chromatic characteristics of red wines are described by the intensity of colour and shade, and are measured using a spectrophotometric method. The intensity of colour is given by the sum of absorbencies (or optical densities) I = A420 + A520 + A620, using a 1 cm optical path and radiations of wavelengths 420 nm (violet), 520 nm (green) and 620 nm (orange). The shade is expressed as the ratio A420/A520 of the absorbance at 420 nm to the absorbance at 520 nm.

Colour is the first impression that the consumer receives from wine and it will influences how they taste the wine. But colour also informs the consumer about a wines quality, age, oxidation and structure, so it has an important repercussion on how they perceive a wine. It is not obvious how to move from what appears an overly complex way to define the colour, to the practicalities of look at a glass of wine before we taste it.
During winemaking some
yeast metabolites react with grape anthocyanins during fermentation forming pigments with slightly different chromatic features. Vitisin A and vitisin B are both natural phenols found in red wine, and both are formed from different reactions with malvidin (M3G in below graphic), a major grape anthocyanin. These are interesting because they have a stable colour intensity under variable pH, are resistant to oxidative damage, and are not sensitive to sulphur dioxide bleaching.

Spectrum of Vitisin A and B

Above we can see that the chromatic properties of vitisins are slightly different from grape anthocyanins. The maximum of absorption in visible spectra for malvidin is approximately 528 nm, but vitisin A shows a maximum of 515 nm and vitisin B of 495 nm. That means that vitisins are red‐orange pigments and consumers currently prefer red‐bluish colours in wines. However, the normal evolution in wine colour during ageing is from purple to red‐orange, and, in this situation, colour of vitisins can be better integrated in wine appearance, and even improve it.

The colour of wine evolves from red‐bluish to red‐orange during the ageing and as seen below this phenomenon is affected by oxygen levels and temperature. During
barrel ageing, micro-oxygenation through the porous surface of wood promotes the browning of the wine pigments, and, at the same time, helps to modulate the aromatic profile and smooths the tannins. It is also known that long reductive ageing, as happens in vintage Porto wines, helps to keep red‐bluish pigments and to preserve initial colour. During ageing, the colour of wine, initially due to grape anthocyanins, is being substituted by polymeric pigments. These pigments could be responsible of 50% of the colour density after the first year.
What is happening is that
polymeric pigments are formed by more than one flavonoid unit, and in the polymer, the colour is due to the anthocyanin moiety but the non‐anthocyanin fraction is affecting the colour tonality. Polymeric pigments show red‐orange colours and higher stability against both oxidative damage and sulphur dioxide bleaching, so they are really important in the colour of aged red wines. The red‐bluish or red colour comes from anthocyanin monomers and a red‐orange colour from oligomeric pigments.

Typical wine colour evolution during barrel ageing

The background for the above description is that some non‐Saccharomyces yeasts promote the formation of polymers better than S. cerevisiae, and therefore mixed or sequential fermentations involving non‐Saccharomyces yeasts could be a way to increase stable pigments in wines. Check out this article for more information on the more general topic of effects of yeasts on wine production and colour.

Wine colour might appear to be one of the most characteristic and predictable feature of a red wine, but many, many things can influence a wines colour. For example, wood is used during the process of red wine
ageing in most of the world’s wine producing regions. During wine ageing in oak barrels, beside oxygen diffusion through the pores, many compounds are extracted into wine and are involved in a great number of reactions phenolic compounds, particularly with anthocyanins. In addition, the oxidation of anthocyanins during wine ageing in oak barrels leads to reduction in red colour and their combination with oak tannins increases their stability and gives the wine a red-purple tone. The relationship between oak wood and the colour of red wine has been studied in depth, but there has also been an interest in using non-oak woods such as cherry and acacia. From a sensory point of view, the red wines aged in contact with oak woods showed a tendency for higher aroma scores than the red wines aged in contact with acacia or cherry woods. However, taste descriptors showed no real differences for red wines. And it would appear that the use of acacia or cherry woods did not introduce any additional variability in wine colour, as compared to the variability already noted between different winemaking techniques and ageing with different oak woods.

Another example concerning the colour of red wines involved the study of "
cover crops" in the Rioja wine growing region. These crops were found to compete with vines for soil nutrients, and modify grapevine development as well as must and wine quality. The alternatives to conventual tillage were barley and clover, and it was found that after four years barley actually decreased plant vigour and increased the polyphenol content and colour intensity, but more so in the must than in the Rioja wine itself.

Frankly, the definitions look complicated, but I can only presume that they are useful in practice.

Sensory characteristics - limpidity


The Rioja rules and regulations mentioned colour as one sensory characteristic, and
limpidity (clear, transparent, bright) as another separate characteristic (the opposite is turbidity). Both experts and regularly consumers tend to focus on colour, intensity and clarity when evaluating the visual appearance of wine. The technologies available are driven by the need to control water supplies, which in itself involves a spectrum of applications from fish farming to cell culture growth. Turbidity is the scattering and absorption of light by solid particles, and scattering can be in all directions, so in effect a non-linear phenomena.

Prior to bottling most wines require some filtration, in many cases through
membrane filters. As wine is a complex medium with a wide variety of constituents, it is not always easy to tell how well the filtration will proceed. Even wines that appear very clear can block filters and cause delay and extra expense if they need extensive filtering prior to bottling. There are two specific tests that can be used to determine how easy the wine will be to filter, and this ease of filtering is commonly known as filterability. The first uses a bench-top turbidity (nephelometery) meter. The second, less common but also important measurement, is to determine the "filterability index".

The
OIV proposes Method OIV-MA-AS2-08 for measuring wine turbidity using a turbidimeter. They also warn the reader that measurements of turbidity are largely dependent upon the design of the equipment, and it's usually not possible to compare results from one instrument to another. The measurement technique uses a nephelometer incorporating a double beam with optical compensation. It is also worth noting that this type of measurement is not comparable with electro-/chemical measurements where clearly defined quantities or concentrations of substances are reacting and can be isolated and analysed.

Observing glass of wine directly against a light source will show any suspended particles. A cloudy wine could be caused by one or more "defects", including excessive contact with the air for a wine not properly stabilised, excessive and sudden temperature changes between cold and warm, prolonged exposure to light, an improperly sterilised bottle, presence of traces of copper or iron, colouring substances or unstable
tannins, bacteriological or microbiological infection, or the presence of yeast's residuals or proteins.

And in addition limpidity is strongly linked to clarification. The removal of colloidal matter and sediment is accomplished by
fining, filtration or both. Fining uses processing aids, or fining agents, to clarify wine to a desired level. Traditional fining agent types include:-
Milk, eggs and shellfish are classified as allergens by regulatory agencies in many countries. Some have implemented mandatory allergen labelling for wines processed with these types of fining agents. Because of increasing consumer concerns about what goes into wine and possible allergies, stricter rules imposed by regulatory agencies, the movement toward more “natural products”, and that some fining agents may strip wines of aromas and colour, the winemaking industry has been researching alternative sources of proteins for fining applications. The Australian Wine Research Institute has an extensive webpage on fining agents.

Of course turbidity measurements beg the question about the need to filter. When the viniculturist has got the complex bond between chemistry and microbiology of the wine right there is no need for filtration. This means that the following criteria have been met:-
  • Alcoholic fermentation is complete, i.e. less than 1g/l of the fermentation sugars glucose and fructose are present.

  • Given that Brettanomyces and Pediococcus are capable of using the unfermentable sugar pentose. Less than 1g/l of pentoses must be present.

  • Malolactic fermentation is complete, i.e. less than 0.2 g/l of the sour tasting malic acid remains.

  • Brettanomyces management has been performed and no Brettanomyces populations are present.

  • The necessary amount of free molecular sulphur dioxide is present in correlation with the pH of the wine, including a small excess to account for loses during and immediately after bottling.

  • The wine is stable in terms of cold stabilisation and protein stabilisation (and pinking in white wines).

  • All visibly suspended solids have settled out completely, including yeasts and bacteria.

  • For blended wines, the final blend should have been stable at cellar temperatures for at least six months.

  • Test bottles of the wine have been stable at room temperature for at least one month.

Unfortunately, if your wine does not meet these requirements filtration will most likely be deemed necessary. The first step might be to opt to use conventional gravity clarification or selective fining agents. Perpendicular flow filtration includes screen filtration, depth filtration and membrane filtration, and filter media can either be diatomaceous earth, or powder, or paper/pads. Cross- or tangential flow filtration involves filtering the wine across the surface of the filter matrix, thereby significantly reducing the potential of the filter to clog and block. Crossflow filtration is used effectively to remove large quantities of solids in a single filtration and is also an efficient technique for cleaning high sugar wines and juices that the perpendicular filters struggle with. Crossflow filtration is a useful tool in removing larger molecules, like proteins and phenolics, achieving protein and colour stability.

There exists also laboratory equipment for measuring of how easy a wine is to filter, i.e. determining the "filterability index" where the higher the number the lower the filterability. This can be very useful when the wine appears clear but has non-particulate materials that can cause filter clogging.

Sensory characteristics - taste


I guess
taste as a sensory characteristic is determined by the statements that:-
  • A young red Rioja must flavour-packed with balanced acidity, alcohol and tannins.

  • A Rioja crianza must have a good body with smooth, tasty tannins.

  • A Rioja reserva must have a good structure and flavours in harmony. It must be smooth and velvety.

  • A Rioja gran reserva must be smooth, fine and elegant, with high persistence.


Wikipedia has a whole webpage dedicated to
wine tasting descriptors, and even a "wheel of aromas", in French, of course (see below).

Roue des Arômes


"
Flavour-packed" is almost everywhere, and it sounds almost self-explanatory, however I've not found a definition of what it actually means.
We are on safer ground with
body, since full-bodied means containing a high alcohol content (>13.5°), and being fuller in the mouth. Other words often associated with full body is richness, weight, complex flavours and powerful aromas, and even "hearty". Some texts mention light body, medium body and full body, but not "good body". Light body is "lean and delicate", with low viscosity, and is easy to drink and pair with light, lean food. Medium body appears to sit between light and full (surprise, surprise). One cool comparison was that light-bodied is like skim milk, medium-bodied is like whole milk, and full-bodied is like cream.
A
smooth wine appears to have a "pleasing velvety texture", associated with soft tannins, so not bitter or astringent. A velvety texture is considered more assertive that a "silky texture".

  • A good structure is

  • Flavours in harmony means

  • A wine that is fine and elegant

  • A wine with a high persistence means

  • Finesse: A wine of high quality that is well balanced
  • Elegant: A wine that possess finesse with subtle flavors that are in balance.
  • Balanced: A wine that incorporates all its main components—tannins, acid, sweetness, and alcohol—in a manner where no one single component stands out.[7][3]

  • There is a clear requirement that participants should be both trained and tested to
    detect the five basic tastes (sweet, sour, salty, umami and bitter) as well as astringency. For the sense of taste, there are five kinds of basic tastes, namely:-
    Concerning taste discrimination, experts should be able to detect concentration >5 g/l sucrose (sweet), >0.5 g/l citric acid (acid), >1 g/l sodium chloride (salty), >0.2 mg/l caffeine (bitter), >0.5 g/l monosodium l-glutamate (umami), and >1 g/l tannic acid (astringency).

    Sensory characteristics - smell


    I guess
    aroma as a sensory characteristic is determined by the statements that:-
    • A young red Rioja must have an intense varietal fruit aroma with floral sensations.

    • A Rioja crianza must have a good harmony between fruit aroma and toasty notes from the oak.

    • A Rioja reserva must have a complex, with well-integrated ripe fruit and spicy aromas (vanilla, roasted coffee, tobacco).

    • A Rioja gran reserva must very complex, intense aromas, with spicy notes (tobacco, roasted coffee, nuts, cloves, walnuts, cedar).






    Olfaction, the sense of smell, is the least understood of the five senses. Although the detection threshold concentrations of substances that evoke a smell are slight, a concentration only 10 to 50 times above the detection threshold value often is the maximum intensity that can be detected by humans. This is in contrast to our other senses where maximum intensities can be many more multiples of threshold intensities. The maximum intensity of sight, for instance, is about 500,000 times that of the threshold intensity and a factor of 1 trillion is observed for hearing. For this reason, smell often identifies the presence or absence of odour rather than quantifies its intensity or concentration. For example, we can detect the presence of chlorine at 0.01 ppm, but we need >0.3 ppm to recognise the smell as chlorine. We can rapidly become tolerant (olfactory fatigue) to higher concentrations, but yet higher concentrations can cause coughing and choking, and severe exposure can cause death. We have a yet lower detection thresholds to sulphur dioxide (0.009 ppm), hydrogen sulphide (0.00047 ppm) acetaldehyde (0.004 ppm). The ability to perceive an odour varies widely among individuals, and there is more than a thousand-fold difference between the least and the most sensitive individuals. In many cases people can be totally insensitive to one or more particular molecules (e.g. 1 in 10 people cannot detect the extremely poisonous hydrogen cyanide). Yet small changes in molecular structure can also lead to large perceptual differences, e.g. the molecule d-carvone smells like caraway seeds, whereas l-carvone smells like spearmint. Unfortunately the olfactory sensory nerves atrophy with age, and our ability to like or dislike a particular odour decreases with age (our olfactory acuity is less than 40% at the age of 60).

    For the
    sense of smell, there are 5 to 10 thousand compounds which can produce different perceptions in a persons brain, however our nervous system integrates the responses from a number of cells to determine the identity of the primary odour stimulus being received (e.g. a perfume or the bouquet of a wine). Based on psychological tests, seven primary classes of olfactory stimulants have been found to preferentially excite separate olfactory cells, namely:-

    Humans can perceive individual odourant molecules (e.g. coconuts and bell peppers have an odour created by a particular molecule, namely lactone esters and the so-called "bell pepper pyridine" respectively), but we usually associate naturally occurring odours as a blend of several odourant molecules. However, the overall perception of a sub­stance as far as its chemical properties are concerned is due to the combination of smell and taste senses, and includes the so called trigeminal sense (responsive to irritant chemical species).

    Concerning the testing of odour discrimination, the guidelines use the following test solutions, i.e. acetic acid solution (0.1 g/l to 0.7 g/l), 2,4,6-trichloroanisole (TCA) solution (1 ng/l to 7 ng/l), ethyl acetate solution (10 mg/l to 100 mg/l), and 4-ethylphenol solution (0.05 mg/l to 0.45 mg/l). Collectively acetic acid and ethyl acetate are responsible for "volatile acidity" in wine, and for a Rioja red wine "volatile acidity" may not exceed 0.05 g/l, for each actual degree of alcohol and may not in any case exceed 0.8 g/l. TCA is often associated with an off-flavour, a musty/mouldy/earthy type odour often termed "cork taint". Tests show a TCA odour detection threshold of about 1 ng/l in red wine (the taste detection threshold was just under 2 ng/l), and above about 15 ng/l the wine would be rejected. 4-ethylphenol concentrations above the sensory threshold (0.15 mg/l) produces an aroma described as barnyard, medicinal band-aid, horse sweat, acid cheese, and mousy, and a wine will usually be rejected above a concentration of 0.25 mg/l. It is produced by the undesirable slow-growing brettanomyces yeast during barrel ageing, and masks more subtle varietal notes (measures are allowed against this yeast).

    Sensory characteristics - wine tasting



    Young Red Wine
    Eye: Purple with bluish hues.
    Nose: Intense varietal fruit with floral sensations.
    Mouth: Flavour-packed with balanced acidity, alcohol and tannins.

    Crianza Red Wine
    Eye: Garnet and cherry red.
    Nose: Harmony between fruit and toasty notes from the oak.
    Mouth: Good body with smooth, tasty tannins.

    Reserva Red Wine
    Eye: Dark-cherry red with a ruby trim.
    Nose: Complex, with well-integrated ripe fruit and spicy aromas (vanilla, roasted coffee, tobacco).
    Mouth: Good structure and flavours in harmony. Smooth and velvety.

    Gran Reserva Red Wine
    Eye: Ruby-red with brick hues.
    Nose: Very complex, intense aromas, with spicy notes (tobacco, roasted coffee, nuts, cloves, walnuts, cedar).
    Mouth: Smooth, fine and elegant, with high persistence.



    https://www.winetasting-demystified.com/wine-tasting-wheel.html


    Below we have
    a typical taster's form for one type of red wine, where each criteria must be assessed value in a small range of options.

    Appearance
    Opacity - The degree to which light is not allowed to pass through a sample
    Purple - Intensity of the colour purple in the sample
    Brown - Intensity of the colour brown in the sample

    Aroma
    Overall fruit intensity - Intensity of the fruit aromas in the sample
    Red fruits - Intensity of the aroma of red fruits and berries, such as raspberries, strawberries, cherries, cranberries
    Dark fruits - Intensity of the aroma of dark fruits and berries, such as blackberries, plums, black currants
    Dried fruit - Intensity of the aroma of dried fruits, such as raisins, prunes, figs
    Oak - Intensity of the aroma of wood, oak, sawdust, wood shavings
    Vanilla - Intensity of the aroma of vanilla
    Sweet Spice - Intensity of the aroma of various sweet spices, such as cinnamon, nutmeg, cloves, aniseed
    Grassy - Intensity of the aroma of fresh cut grass, leaves, stalks
    Mint - Intensity of the aroma of mint, menthol, eucalyptus
    Green Capsicum - Intensity of the aroma of fresh green capsicum (green
    bell pepper)
    Cooked Vegetables - Intensity of the aroma of various cooked vegetables, and the water vegetables have been cooked in
    Earthy - Intensity of the aromas of wet earth and organic matter
    Dusty - Intensity of the aroma of dust
    Smokey - Intensity of the aroma of smoke, burnt or charred wood
    Pungent - Intensity of the aroma and effect of alcohol

    Palate
    Overall fruit flavour - Intensity of fruit flavours in the sample
    Red fruits - Intensity of the flavour of red fruits and berries, such as raspberries, strawberries, cherries, cranberries
    Dark Fruits - Intensity of the flavour of various dark fruits, such as blackberries, currants, plums
    Oak - Intensity of the flavour of oak, wood, sawdust
    Green - Intensity of the flavour of green stalks
    Sweet - Intensity of sweet taste, i.e.
    sucrose
    Viscosity - The perception of the body, weight or thickness of the wine in the mouth (from 'low' meaning watery, thin
    mouthfeel to 'high' meaning an oily, thick mouthfeel)
    Acid - Intensity of acid taste in the mouth, including
    aftertaste
    Astringency - The drying and mouth‐puckering sensation in the mouth, including the textural, mouth‐coating aftertaste that lingers after
    expectorating
    Bitter - The intensity of bitter taste perceived in the mouth, or after expectoration
    Hotness - The intensity of alcohol hotness perceived in the mouth, after expectoration ('low' meaning warm to 'high' meaning hot)
    Fruit aftertaste - The lingering fruit flavour perceived in the mouth after expectorating.

    One of the more expensive ISO standards is
    ISO 5492:2008 and concerns the vocabulary to be employed in sensory analysis, which I guess would need to be customised to wine tasting, and perhaps to the specific wine or wines being tastes, as well as the overall objective of the tasting. However, the above taster's form for a red wine is sufficiently clear for the purposes of this webpage.

    I've seen
    tasting forms that vary considerable, going from a binary choice (yes/no or 0/1) concerning two different colours and the "clearness" of the wine, through a 0-1-2 for typicality, to a 0 to 6 for the aromas, and a 0-10 for taste. Other tasting forms included light-amber, amber, dark-amber, brick-red, reddish, brown, and even sour-cherry for colour. Another tasting form looked to isolate primary, secondary, tertiary and quaternary aromatics (often termed "bouquet"), and yet another tasting form brought together olfactory, gustatory and trigeminal sensations under the heading "flavour".

    One particular tasting form was aiming to isolate the
    presence of defects, e.g. ester-like (of varnish, glue, herb), burning (sharp, of alcohol), toast crust-like, herbaceous (of grass), burnt, smoky (smoke-like), mouldy (of mould or dampness), stale (of stagnant marsh), dish-like, plastics-like, rubbery, thoroughly cooked-like, flat (of filter paper), cloth-like (of wet tea-towel), pod-like, earth-like, strange, flat, one-sided, rancid oil-like, sourish, metal-like, oil-like (petroleum), aromatised, strawy (of hay), chemical (acetone, acrolein, hydrogen sulphide etc), woody (rough), aldehid (of green) etc.

    Another tasting form focussed on
    subjective aromas, with unpleasant (repellent), pleasant (likeable), short (quick-cutting), long (long-lasting), tender, nice, rich, poor, luxurious, complex, velvety, hard (robust), strong, exuberant, delicate, floral, fruit, refined (noble), vanilla-like, artificial, overly sweet, specific (distinct), vegetative, chemical, etc.

    In many cases
    taste was a key characteristic, but the criteria (and vocabulary) could range from the precise to the very open-ended, e.g. empty (weak), semi-empty, medium full, full, markedly full, oil-like, astringent, acrid, acerbic (harsh), non-harmonious, medium harmonious, harmonious (tuneful), completed, light, heavy (tiring), prickly, herbaceous (of grass), petroleum-like (of oil), soapy, honeysweet, fruit, meadow-like, thoroughly cooked-like, floral, cute (of alcohol), rancid, non-drinkable, moderately drinkable, drinkable, markedly drinkable, fluttery (velvety), velvety, spicy, vanillin-like, plastics-like, metal-like, dry, insipid, sourish, sour, markedly sour, one-sided (not nice), blunt (tired), mild, rubbery, undeveloped, developed, defective, sweetish, burnt, smoky (smoke-like), aldehid (of green), perfume-like, aromatised, refreshed, thoroughly cooked, etc.

    As seen above tasting vocabularies can have an enormous variety and will depended on the expertise of the tasters, however much additional information can be gained from identifying
    alterations (defects) in the wines.

    Any testing or training for the tasters would usually also include the
    detection of common defects (presented in black glasses), and the evaluation of different types of tannins, using 0.1 g/l samples of anthocyanidic tannins (grape) and gallic and ellagic tannins (from oak).

    The main
    visual alterations in red wine samples are:-
    • Browning (premature oxidation, oxidation of polyphenols) is far less common than in the past, and red wines can withstand significant oxidation during handling due to the higher content of phenolic compounds, which are natural antioxidants

    • Hazy appearance (wine yeast and bacteria) is a reference to the amount of light that can (or cannot) pass through the wine

    • Lack of colour (lack of pigments and excess sulphates)

    • Premature brick-red colour (insufficient tannin-anthocyanin combination)

    • Bubbles in a red wine, along with a yeasty smell and taste, suggest a secondary fermentation in the bottle due to an excess of residual sugar (there are some red wines that are intended to be "frizzante").


    Olfactory alterations include:-
    • Herbaceous like freshly cut green grass and leaves (cis-3-Hexen-1-ol, also known as leaf alcohol). Cut grass can be pleasant or become an off-note if too strong, and may be due to the wine grapes not being fully ripe at harvest.

    • Green bell peppers (from 3-Isobutyl-2-methoxypyrazine). The green bell pepper odour appears to be related to excessive leafy parts of the vines, and thus can be managed by pruning and better vineyard management.

    • Freshly turned wet earth, mushroom or musty odour from geosmin, which is very similar to the odour of rain hitting the ground. It can impart a pleasant note, but becomes a fault is too pronounced. It is related to the complementary action of two fungi, botrytis cinerea and penicillium expansum.

    • A dusty, musty, mouldy, damp cellar aroma comes from 2,4,6-trichloroanisole related compounds, and is typically called "cork taint", i.e. an off-aroma transferred to the wine from moulds growing on the cork. It is one of the most odour intense compounds known and the consumer rejection threshold of only 3.1 ng/l has been reported, whilst the consumer detection threshold was 2.1 ng/l. There are several other compounds responsible for cork taint.

    • A sharp odour of vinegar from acetic acid is directly linked to volatile acidity which for Rioja red wines should not exceed 0.05 g/l, and may not in any case exceed 0.8 g/l. Increased levels of acetic acid in stored wines are usually attributable to growth of acetic acid bacteria (generally of the genus Acetobacter).

    • Nail polish remover or solvent odour from ethyl acetate, can contribute to the sensory perception of volatile acidity. Ethyl acetate is the major ester produced by yeast and at low levels can contribute ‘fruity’ aroma properties and add complexity to wine, but rapidly becomes a defect at higher levels. Factors that can influence ethyl acetate formation by yeasts include the yeast strain employed, temperature of fermentation, the amino nitrogen content of the juice and sulphur dioxide levels. Ethyl acetate is also produced by acetic acid bacteria.

    • A pungent smell of rotten egg, onion, garlic, cooked cabbage, canned corn, or even burnt rubber (so-called "reductive" off-odours caused by low volatile sulphurous compounds). Sulphur compounds occur naturally in wine due to the metabolism of the microorganisms (yeasts and lactic acid bacteria) involved in fermentation. At low levels it can add a truffle, mushroom, radish, or green olive-like smells to wine. These have been accepted as positive traits and increase complexity in the wine, but at higher levels, they become a fault. Most winemakers will be familiar with the aroma of hydrogen sulphide or "rotten egg gas", and the detection threshold in wine is very low, at about 1-2 µg/l (parts per billion). The various forms of sulphur (e.g. sulphate, sulphite and sulphur-containing amino acids) are important for yeast biosynthesis. During alcoholic fermentation, yeast will excrete hydrogen sulphide into the fermenting juice when placed under stress, e.g. when the yeast starts to run out of nitrogen. Some winemakers remove excess hydrogen sulphide from red wines by aerating at the first racking, thus volatilising it. Many winemakers remove objectionable hydrogen sulphide by fining with copper sulphate, i.e. copper sulphate reacts with hydrogen sulphide to form copper sulphide, which is highly insoluble. Aromas described as cabbage, garlic, onion and rubber are due to compounds known as "thiols or "mercaptans". Their presence in wine above the threshold is generally regarded as a defect, however, the odour of these sulphur compounds is important to many foods. Ethyl mercaptan (ethanethiol) has an onion-like or rubber-like aroma, and the odour of methyl mercaptan is usually described as rotten eggs or cabbage. Removal of these defects requires the creation of reducing conditions, by the addition of ascorbic acid and sulphur dioxide, in order to reduce these compounds back to the reactive species (methanethiol and ethanethiol), which may then be removed by treatment with copper.

    • A pungent penetrating aroma, similar to a just-struck match, which reacts strongly with receptors in the nose (olfactory nerve) causing sneezing and often a choking sensation typical of free sulphur dioxide. It is one of two preservatives permitted for use in wine production in most winemaking countries, the other being sorbic acid. Total sulphur dioxide (expressed in milligrams per litre) must not exceed 140 mg/l for Rioja red wines with less than 5 grams of sugar per litre. It must not exceed 180 mg/l, and for red wines with 5 or more grams of sugar per litre, and once the fermentation process is over for a dry red wine, the total sulphur dioxide must not exceed 100 mg/l. Winemakers add sulphur dioxide to wine to minimise the effects of oxidation and also to inhibit microbiological activity, and total sulphur dioxide represents the sum of both the free and bound fractions. It is the molecular form of sulphur dioxide that is responsible for the antimicrobial effect and is the form that we can smell when too much is added.

    • A pungent smells of horse barn, medicinal band-aid, and sweaty leather saddles, is due to 4-ethylphenol concentrations, and is produced by the undesirable slow-growing brettanomyces yeast during barrel ageing. Some people love low level woodsy and leathery aromas but they are generally considered a wine fault. The presence of the yeast is associated with barrels and winemaking equipment that have not been properly cleaned.

    • A cardboard, straw or hay-like aroma means that the wine has become oxidised. The sensory characteristics of oxidation can range from a dulling of the aroma, to the extreme "wet wool" or varnish-like aroma. In some wine styles, such as sherry, oxidation is deliberately encouraged.

    • A stale/rancid odour of "over-ripe bruised apples" or sherry and "nut-like" characters, is due to acetaldehyde (ethanal) concentrations above about 125 mg/l. Yeast can oxidise ethanol to acetaldehyde under oxidative conditions, and ullaged in tanks can lead to surface yeast infection where acetaldehyde is produced. Ethanol represents the primary source of carbon in aerobic film-yeast growth, and acetaldehyde levels will increase as wines age due to chemical oxidation of ethanol. Apart from chemical and microbiological formation, winemaking practices can influence the level of acetaldehyde present in wine, i.e. addition of sulphur dioxide during fermentation can increase the concentration of acetaldehyde, as can increases in pH and fermentation temperature.

    • A "mousy taint", an off-flavour reminiscent of caged mice, may be perceived late on the palate or after the wine has been swallowed. It tends to linger and leave a most obnoxious taste in the mouth, but those who move quickly to the next wine in a line-up might miss it. Mousy taint is rarely detected by sniffing because the compounds involved are not volatile. The main compound responsible for "mousiness" is 2-acetyltetrahydropyridine (ACTPY). Usually of microbial origin, most strains of lactic acid bacteria can produce the taint, and it is more likely to occur in wines with low concentrations of sulphur dioxide and low acidity. A suggested approach is to focus on cellar hygiene to prevent unwanted microbial growth and the possible formation of "mousiness", e.g. increasing total sulphur dioxide to between 50 and 80 mg/l.

    • The odours of plastic, paint, or medicinal are associated with a numbers of chlorophenol compounds, notably 2,4-dichlorophenol. Chlorine-based sterilising agents, such as hypochlorite solutions, can react with traces of phenol present in materials such as plastic or fibreglass tanks or linings, phenolic-based resins, paints and fittings. Sometimes wooden pallets loaded with cartons are stored near processing areas where disinfectants containing available chlorine are used. In situations such as this, chlorophenols can be generated in the cartons or pallets if they contact chlorine. In addition, products such as fibreboard and paper made from recycled materials can often contain relatively high levels of chlorophenols, which can then contaminate food products or packaging made with fibreboard or paper.

    • An undesirable smoky character is associated with guaiacol (and 4-methylguaiacol), associated with heavily toasted oak barrels. Guaiacol, along with other oak volatiles, increase during the barrel toasting process. Intense toasting is liked with the formation of various volatile phenol compounds that are extracted from oak and pass into wine during storage. The composition reflects the structure of the lignin in the particular oak, as well as the toasting temperature.

    • A wine smelling "jammy" that is also bit amber-tawny and tastes roasted can be due to the bottle being exposed to too much heat, i.e. poor transport, storage, etc.


    Taste alterations include:-
    • The oxidation flavour is due to multiple compounds including a range of aldehydes (e.g. vanillin is one of this group, as is acetaldehyde which is often associated with a hangover). Aldehydes produce both the taste and odour of "over-ripe bruised apples" or sherry and "nut-like" characters, and are associated with a loss of colour brightness and a browny colour.

    • The "cork taint" is a combination of aroma and taste often mentioned as wet newspaper to mouldy cardboard.

    • A "eucalyptus" aroma in red wines has also been described as being spicy and mint-like. This character in wines has typically been attributed to the monoterpene compound 1,8-cineole (1,3,3-trimethyl-2-oxabicyclo-[2.2.2]octane) which is commonly known as 'eucalyptol'. Eucalyptol has been described with terms such as fresh, cool, medicinal and camphoreous. One proven route is where gum trees are growing close to vineyards. They give off the highly volatile eucalyptus oil in warm conditions, with the oil vaporising, becoming airborne, and coming to rest on the surface of grape berries. The character is generally reported to be more pronounced in red wines because red wine fermentations are performed with the grapes in contact with their skins, and thus the oil is extracted from the skins into the wine.

    • Mousy taint is an off-flavour reminiscent of caged mice or sometimes cracker biscuit. The taint is generally perceived late on the palate or after the wine has been swallowed or expectorated and usually takes a few seconds to build. It tends to linger and leave a most obnoxious taste in the mouth for some time. If a taster moves quickly to the next wine in a line-up, they might miss a mousy wine. Mousy taint is rarely detected by sniffing because the compounds involved are not volatile at wine pH. Note that there is considerable variation in the sensitivity between individuals to the taint. There is no satisfactory method to remove a mousy off-flavour, but it is more likely to occur in wines with low concentrations of sulphur dioxide and low acidity.

    • Unripe grape or lemon taste suggests that some grapes have been picked before they were ripe. Unripe grapes have a high acidic content and a sour, sweet-tart flavour, and to make a good wine you need ripe grapes. Some winemakers have shifted to picked grapes later in order to obtain a red wine with a darker, more concentrated look, and a sweeter fruit profile with more alcohol. When coupled with expensive new oak, they are often termed the "international style", i.e. different from the classical European models. Some experts argue that these denser, riper, and more alcoholic wines, created through later picking, lower yields, more ruthless selection, and the use of increasing proportions of new oak, have lost the sense of place (the terroir). So in contrast, some consumers are looking for something different, and have turned to "greener" wines. However, "green" wines become even more green as they age, so the lesson is "herbaceous is good, greenness is not".

    • A harsh, bitter taste like that of raw chicory, unsweetened cocoa, green tea or quinine, points to tannins and possibly quinine sulphate. Tannins add bitterness to the wine, a bit like the taste of a bag of wet black tea which is almost all tannin. If the bitter quality dominates the wine's flavour or aftertaste, it is considered a fault. In young red wines bitterness can be a warning signal, as it doesn't always dissipate with age. Normally, a fine, mature wine should not be bitter on the palate. Quinine has been used for some considerable time in a variety of drinks, e.g. quinine tonic with gin, quinine and Dubonnet, or mixed with sweet Malaga wine, or even Barolo (and 12 grains of quinine sulphate mixed with Madeira or Malaga wine was an early medicinal concoction).

    • A rough, harsh taste that makes your mouth pucker, is usually from tannin or high acidity, and when it stands out, the wine is called astringent. The cause is a chemical compound that makes body tissue and blood vessels contract, and the biggest contributor to the level of astringency felt in a wine is polymeric flavan-3-ols, a building block of anthocyanidins or common plant pigments. Flavan-3-ols is mostly associated with grape seeds, and appears to increase the later the harvest.

    • The attributes acidic, bitter and astringent are considered defects only when excessive and the wine structure lacks balanced.


    There are a number of different ways to
    organise a sensory analysis of wine, including:-
    • Triangle - tasters assess three samples, then pick the sample which is different from the other two, or the odd one out

    • Duo-trio - tasters assess a reference, then the two test samples, and must indicate which test sample is the same as the reference

    • Paired comparison - tasters are asked to identify which sample is higher in an attribute (e.g. identify which sample is sweeter)

    • Same/different - tasters assess both samples and indicate whether they think the samples are the same or different

    • Paired preference - tasters assess both samples and indicate which one they prefer (they cannot say neither)

    • Descriptive tests - there might be a need to first perform "discrimination tests" and then follow that with "descriptive tests" to provide a quantitative measure of a wines characteristics that might allow a comparison between two products.


    The "
    Office Internationale de la Vigne et du Vin" has also published a standard for international wine competitions. The object is somewhat different from a wine tasting to identify defects or isolate preferences resulting from a change in winemaking practices, etc. Firstly, there is a complete segregation concerning the type of wine (e.g. sparkling whites through to still reds and spirits) and including the definition of sub-groups based upon sugar content and overpressure (i.e. still red wines should be separated into two sub-groups, above and below 4g/l of sugar). All samples must be certified for alcoholic strength, sugar (glucose+fructose), total and volatile acidity, and total and free sulphur dioxide. However, the actually assessment of the still red wines is confined to attributing numerical scores to a small number of variables, and an overall "harmony" judgement. The wine's appearance is evaluated for limpidity and "other aspects, excluding limpidity" (so colour, intensity, viscosity). The wines nose for genuineness, positive intensity, and quality. And the wines taste for genuineness, positive intensity, harmonious persistence, and quality. The possibility exists to reject a wine due to a major defect.
    Genuineness appears to be about identifying any viticulture based defects, or oenological characteristics that are foreign to the specific wine. Quality touched on both aroma and taste. Complexity, richness and finesse of the aromatic palette is about perceiving several and changing odours. The priority for taste is richness which is an overall impression of aromas (complexity), structure (acid, tannins, alcohol), coating elements (fatty), residual sugars, and bitterness.
    In addition
    persistence is isolated as a separate evaluation criteria. This is about measuring the length of residual olfacto-gustatory sensation. This descriptor is equal to one time measurement, and is calculated in seconds (caudalie), starting once the wine has left the mouth. Counting is done by chewing and discreetly opening the lips and exerting a small depression in the mouth to allow air to enter. Slow chewing corresponds to approximately 1 second.
    Finally the overall "
    harmony" judgement can include an analysis of the difficult issue of typicality and appraisal of potential of the wine to evolve over time.



    Sensory characteristics - grapes tasting



    People tend to think of wine when a tasting is mentioned, but
    grapes can also be tasting as well. Many would claim that wine grapes are far more heterogeneous than wine, since their composition evolves much during ripening and varies with the grapes origin. One particular point often mentioned is that grape tasting is all about identifying the characteristics, and not if they are pleasing or not. Generally there are 20-30 descriptors and each can simply be low, medium or high. It starts with the bunch of grapes (size, shape, compact/loose, wings/fishtail, colour), and heterogeneity of the sizes, shapes, colours. The more heterogeneous the more berries will need to be tasted. It's interesting to note that below-spec berries can have a high impact on the style of wine, e.g. just 10% of insufficiently ripe skins can force the winemaker to shorten the maceration cycle to avoid excessive greenness (i.e. a slight smell/taste of green vegetables).

    Grape Colours

    Here is a list of some of the most important wine grape descriptors:-
    Berry colour - this means that the average colour of the selected grapes must be estimated as well as the percentage of "red" grapes, as opposed to the more mature "dark red" and "black" or "dark blue" colours. It is the red grapes that will force the winemaker to adapt. So grapes should be first assessed for their size (large, medium, small) according to the variety and location in the vineyard. The colour must be assessed in the last fully coloured skin zone nearest the pedicel (stem has a different meaning to a viticulturist). The colour of the pedicel and the transparency of the berry are also assessed. If the berries show too much heterogeneity, then the inspection should be done for different groups, i.e. low-colour, medium-colour, and high-colour.
    Elasticity - the berries should be slightly pressed between the fingers to assessed their mechanical fragility (i.e. little resistance, elastic, high-plastic).
    De-stemming - the berries should be de-stemmed and assessed, i.e. was it easy and did the pedicel have almost no attached pulp, or was the pedicel difficult to remove and did it come out with large part of the pulp, or was the pedicel difficult to remove (the "brush" is the connection of the pedicel and the vascular bundles inside the grape).
    Colour of juice - pressing lightly the grape and examining the colour of the juice obtained. For red grapes, poor (low) would be a yellow-green juice with hints of pink on the outside of the drop, average (medium) would be a light pink juice with hints of red, and mature (high) would be a dark pink juice with abundant hints of red.

    Grape Berry Diagram

    Now comes the issue of taste which requires a certain expertise and practice (above on the right we can also see the berry flavour zones). You need to put three similar berries in the mouth and separate with the tongue the pulps, skins, and seeds, without touching the skins with the teeth. In winemaking the initial grape juice will usually contain something between 7% and 23% of pulp, skins, stems and seeds.
    Fluidity of the pulp - this is the ease of separation of the pulp and skin, and a "high" would be when the pulp melts and becomes quickly liquid, leaving no pulp inside the skins.
    Sweetness, acidity, herbaceous flavours and fruity flavours of the pulp - during the separation of the pulp and skin, the pulp must be tasted for sweetness, acidity, herbaceous flavours and fruity flavours. The skins need to be kept separated between teeth and cheek. The seeds should be spat out onto a paper and examined. Assess the colour and if pulp was attached or not. Assess if the pulp separated easily from the skin, in particular if the pulp melted quickly and there was no pulp left in the skins. This routine appears to also suggest that the sweet and acidic sensations are assessed on the "main sweetness and acidic zones of the tongue". However, it is a fallacy to think that the tongue has well defined sweet, bitter, sour and salt areas. Whilst there is a specific taste receptor for sweet, and bitter activates a different receptor, the different receptors are found across all the "taste areas" in the mouth (taste buds contain a mixture of receptor cells). In addition, we now know that messages are sent to the brain via two specific cranial nerves, one at the back of the tongue and one at the front, and that we have special neurons attuned to a particular taste (and not taste zones on the tongue). Nevertheless many experts still suggest using the front part of the tongue as the "sweet" receptor, so I presume this is more about training and experience than physiology. The viticulturist is then expected to go on and assess also the "herbaceous" and "fruity" flavours of the pulp. High intensity "herbaceous" is like biting into a fresh green bell pepper, and high intensity "fruity" means a jammy flavour for a specific fruit (and not just a general "fruit" appreciation).
    Tasting the skins - The skins should be chewed in the area of the last premolar and first molar (always making the same number of bites (e.g. 10) with the same muscular effort). The ease of chewing must be assessed, including the amount of pulp stuck in the skin, and if possible the acidity and flavours of the juice released, at different times during chewing. Leaving the skins in place between the teeth after chewing, it is now time to assess dryness and astringency of the mix of saliva and juice from the skins.
    Aptitude of the skins to trituration (crushing) - a simple low-medium-high.
    Acidity of the skins - the acidic sensation must be assessed during chewing on the skins, in particular between the 4th and 5th bite.
    Herbaceous flavours - at the same time as evaluating the acidity, determine herbaceous flavours as null, low/medium and high.
    Fruity flavours - make the same evaluation as above, but classify according to null, medium (fresh fruit), and high (jammy).
    Acidity of the skins - make the same assessment of acidity during the 8, 9 and 10 bites.
    Herbaceous flavours - as for acidity at the end of the chewing phase.
    Fruity flavours - as for acidity at the end of the chewing phase.
    This kind of assessment gives in the winemaker a feel for the acidity, flavour and tannic profile, and what might be the outcome of a shorter or longer
    maceration process.
    Tannic intensity of the skins - after chewing, with the tongue, pass the juice extracted from the skins on the palate. Pass two times the tongue on the palate starting from the back of the mouth until touching the incisors. Each passage should lasts one-second with a one-second interval between two passages of the tongue. The friction that the tongue encountered during the second passage should be assessed as low, medium or high.
    Astringency of the skins - with the tongue, gums over the upper incisors should be wet with the mixture of saliva and juice extracted from the skins. Spit the mix of saliva, juice from the skin and skin fragments, if possible on a white background (paper or plate or plastic cup), or on the ground in the vineyard. Within 2 seconds after spitting, pass the upper lip on the upper incisors twice, with the so-called "rabbit mouth movement". Each passage should last one-second with a one-second interval between two passages of the lip. The astringency should be evaluated at the second passage of the lip.
    Dryness of the skins - Two-seconds after assessing the astringency of the skin, pass twice the tongue on the palate, from the back to the front until it touches the incisors. Each passage should last one-second with a one-second interval between two passages of the tongue. The friction and resistance that the tongue encounters during the second passage should be evaluated, as should the difficulty to salivate again. In addition the tactile aggressiveness, and the tannin grain and roughness should be assessed.
    Aspect of the spit mixture of saliva and skin fragments - the appearance of the mixture saliva, skin fragments and skin juice that has been spit out should be assessed according to low (light red-blue liquid with medium size fragments), medium (dark red-blue liquid, with small fragments of skin), and high (very dark blue liquid, dark blue paste, homogenous, almost no visible fragments).
    Colour of the seeds - low (white or yellow green), medium (brownish-green), or high (dark brown).
    Resistance of the seeds - only for the dark brown seeds, introduce two or three seeds between the incisors and apply an increasing pressure. Then assess the fragility by chewing to reduce the seeds into fragments (low, medium, high).
    Ripe flavour's of the seeds - low (green, herbaceous), medium (toasted), high (smell of coffee).
    Tannic intensity of the seeds - pass the tip of the tongue on the fragments of the seeds then, pass these fragments on the palate and gums. Pass twice the tongue on the palate starting from the back until touching the incisors. Each passage lasts one-second with a one-second interval between two passages of the tongue. Evaluate the friction and resistance that the tongue encounters during the second passage (low, medium, high).
    Astringency of the seeds - pass twice the upper lip over the gums and the incisors. Each passage lasts one-second with a one-second interval between two passages of the lip. Evaluate the friction and resistance that the lip encounters during the second passage.

    The above analysis might appear quite complex, but it is only the first step to making a decent wine. The key is to understand the berry, pulp and seed profiles and adapt the winemaking process. Based upon the berry and pulp tasting, an expert might decide how to approach extraction, reinforce or not the colour, decided on the maceration cycle, determine the yeast strain to be use to obtain the best mouthfeel, manage the pH, etc., and possible also decided on the use of oak fragments. These choices should be confirmed by the skin tasting, and the tasting should also confirm the best way to avoid braking the seeds during pressing and maceration. The expert winemaker will need to understand how to best extract the fruit aromas, pigments and polysaccharides from the pulp and skins, and the hydrosoluable tannins from the skins. The will need to avoid amplifying any aggressive tendencies by picking the right yeast strain, the right fermentation cycle, the right oxygenation program during maceration, the right bacteria strain and right time of inoculation, the right program for racking, actions needed during the malolactic fermentation, preparation for barrel ageing, etc.


    https://www.frontiersin.org/articles/10.3389/fbioe.2016.00081/full






    Sensory characteristics - the quality of wine



    Let's look at each of these
    organoleptic characteristics for Rioja red wines, and starting with the easiest, the "quality" of the wine.

    It may appear non-intuitive that "quality" is one of the easiest characteristics to define for Rioja wines. Some people argue that it is subjective, and will depend upon a magical mix of
    terroir, climate, the wine grapes and vineyard management, the winemaking process, and finally the wines appearance, aroma, taste, etc. There are those who have a more technical focus, and mention geology, water-holding capacity, pruning, canopy microclimate, anthocyanins, etc. The viticulturist would certainly argue that wine quality was dependent upon the raw materials, i.e. grape sugars, acidity, tannic substances, aromatic compounds, and in particular the phenolic component in red wines that influences colour, taste, and overall longevity. Other viticulturists would prefer to stress tradition and letting nature run its course, with small berries, old vines, limited yields, narrow rows, vertical trellises, etc. And there are those that look to sensory descriptive analysis, and linking positive feedback with practical improvements made in the vineyards and wineries. Mouthfeel, along with taste, smell and texture, is often mentioned as a fundamental sensory attribute.
    And what about
    ageing potential, stylistic purity, varietal expressions, balance, harmony, complexity, uniqueness? Geographic origin and reputation strongly influence wine connoisseurs, and history and traditional are central to the quality percepts embodied in most appellation control laws. However for the "average" wine drinker, knowledge of geographic or varietal origin tends to be secondary, and for them, ease of availability, price, and previous experience are the overriding factors in selecting one wine over another. Pleasure on consumption is usually assessed on subjective, often highly idiosyncratic criteria. Is it better to rely on the results of blind-tasting by experts, or is "quality" just about delivering "sustainable consumer satisfaction"?
    Maybe the real definition of quality is best seen
    when people don't like a particular wine. It may be difficult to agree on what makes a wine of "quality" but almost everyone knows when a food (or wine) is tainted or has an off-odour (or just an atypical odour), e.g. cork-taint (TCA and TBA), heat damage (maderised, baked) and premature oxidation, goût de lumière (excessive exposure to ultraviolet light in white wine), guaiacol (undesirable smoky taste), too much ethyl acetate (smell of nail polish remover), acetic acid (vinegar smell and taste from a poorly controlled fermentation), too high level of acetaldehyde ("green apple"), too high a level of fusel alcohols mask the fruit and produce a harsh aroma and taste, too much sulphur dioxide (burnt rubber), etc.

    Rioja and Bordeaux have a
    hierarchy of quality which is completely different. Bordeaux's focus is cadastral (possible right down to the plot where the grapes were grown), whereas Rioja imposes a bottom to top hierarchy with Joven (young), Crianza (aged), Reserva, and Gran Reserva. This was established according to the time that the wine spent in oak barrels and then in bottles in the bodega, before being marketed. So in Rioja its the length of ageing that conditions access to each of the quality categories, i.e. the longer the ageing, the higher the wine is in the quality hierarchy.

    Until recently (2019) the regulatory system (Consejo Regulador) for
    Rioja wines used oak-ageing as the only effective indication of quality, and the assumption was that regional specificity did not impact on the quality of the wine. The new regulatory system now also allows wineries to mention both regional microclimates and singular vineyard sites. The three official growing zones still exist, namely Rioja Alta, Rioja Oriental and Rioja Alavesa, as do the four ageing classifications, namely Joven (young), Crianza (aged), Reserva, and Gran Reserva.

    It may surprise some people that Spain was one of the first countries to introduce a national system to link wine to "place". At the beginning of the 20th century, the need for wine regulations became self-evident in the fight against wine fraud, where quality wines were routinely being diluted with low-quality bulk wine.

    Rioja was a leader in the charge for legislation to guarantee wine origin. In 1902, a Royal Decree defined the origin of its wines by establishing a geographical link between the name of a product and the place where it was produced. Just a little over two decades later, in 1926, the first Consejo Regulador (Regulating Council) was created in Rioja. In the years that followed,
    Jerez and Málaga also gained regional protection.

    The most significant move towards quality came with the passage of the 1932 Wine Statute. This law officially created the
    Denominación de Origen/Denomination of Origin (DO) system. Nineteen DO's were officially awarded, and each was allowed to create their own Consejo Regulador. This law remained in effect until it was replaced by the Statute on Vineyard, Wine and Alcohol Regulations in 1970. This law, in addition to delineating production zones, defined production methods and created a national monitoring body.

    In 1988, a new Royal Decree established criteria for the creation of a superior quality level which would rank above the DO designation in both quality and prestige, namely the
    Denominación de Origen Calificada/Qualified Denomination of Origin (DOCa). In an effort to better align Spanish agriculture within the EU system, Spain, in 1996, unveiled its own multi-tiered, sub-classification system. Finally, the Wine Statute was again updated in 2003. In this revision, both the Vino de Pago/Single Estate (VP) and Vino de Calidad con Indicación Geográfica/Quality Wine of Geographic Indication (VC) were created.

    Spain Wine Quality

    Spain’s wine quality pyramid is more specific regarding quality and geographic origin than EU requirements. The official classifications are as follows:-

    • Vino de Pago (VP) are wines produced under a single estate category. Wines must be made under the distinctive conditions representative of the area and must be produced and bottled wholly within the estate. In 2021 there were 20 Vinos de Pago.

    • Denominación de Origen Calificada (DOCa) is the category that represents the highest level for a wine appellation in Spain. The region must have had DO status for a minimum of 10 years. Wine must be produced and bottled within the region, and wines must cost at least double that of the national average for DO wines. Currently, only DOCa Rioja and DOQ (Catalan) Priorat occupy this elite category.

    • Denominación de Origen (DO) is a category comprising the largest portion of Spain’s quality pyramid. A number of quality standards must be met for an appellation to gain DO status, including the use of authorised grape varieties, production levels, winemaking methods, and ageing regimen. Zones of production need to have been recognised for their quality for a minimum of five years. In 2019 there were 68 DO's.

    • Vino de Calidad con Indicación Geográfica (VC) is a category that is a kind of a “stepping-stone” to DO status. Wine appellations in this category are typically in limbo between the Vino de la Tierra and Denominación de Origen categories. A region must spend a minimum of five years as a VC prior to applying for DO status. In 2019 there were seven appellations with VC status.

    • Vino de la Tierra (VT) is the only label under the European Union’s “Protected Geographic Indication” category. Wines in this classification possess identifiable local characteristics but have more relaxed viticultural and vinicultural standards than those of DO/DOCa appellations. Due to the greater flexibility within this category, many winemakers in high-quality regions have opted to label some of their wines as VT. In 2018 there were 42 VT's in Spain.

    • Vino de España/Vino are wines previously labeled "Vino de Mesa", and they represent wines produced without any specific indication. Wines labeled as such are only authorised to mention country of origin, grape variety, and harvest year on the label. Similar to the 20th century Super Tuscans of Italy, many Spanish winemakers intentionally declassify their wines as "Vino de España" in order to increase flexibility in blending options as well as in the utilisation of non-traditional winemaking techniques.


    This classification system has taken root nationally, however many wine appellations are following the example of Rioja wines and are also creating individual
    terroir classifications to further delineate the quality within their respective areas.

    Rioja Wine Classification

    With the most recent changes (2019) in the Rioja regulatory system (Consejo Regulador) the minimum ageing requirements for each quality level also changed:-

    • Vino joven (literally “young wine”), remains un-oaked, from the most recent vintage, and is made to be consumed young (it can also be labelled "sin crianza").

    • Vino de crianza had to be aged for two years, with at least one year in oak barrels. Now ageing must take place in a registered winery, so that it can be inspected regularly, etc. And it is the Control Board (Consejo Regulador) that determines when the ageing period starts. The new rules demand that ageing must be for at least two calendar years (for red wines). The wines must be subjected to the traditional mixed ageing system in oak barrels of approximately 225 litres capacity, continuously and without interruption for no less than one year (for red wines). And this period must be followed and complemented with ageing in the bottle.

    • Reserva had to be aged for three years, with at least one year in oak barrels. Now a "reserva" must be ageing in oak barrels and in the bottle for a total period of at least thirty-six months, with a minimum of twelve month barrel ageing, followed and complemented by a minimum six months ageing in the bottle.

    • Gran Reserva had to be aged for no less than five years, including at least two years in oak barrels. Today ageing in oak barrels and in the bottle must be for a total period of at least sixty months, with a minimum twenty-four months barrel ageing, followed and complemented by a minimum twenty-four months ageing in the bottle.

    • "Viñedos Singulares" is a new classification that requires that the vineyard is at least 35 years old, that the grapes are entirely hand harvested and that an independent tasting committee must note the wine as 'excellent'. In addition, the winery must prove that the exclusive production from that vineyard will be available for a minimum period of 10 years without interruption, e.g. leases on rented vineyards must be valid for at least 10 years, etc. There is also a maximum permitted yield of 5,000 kg/ha for red varieties, and a maximum grape-to-wine ratio of 65%. Only then can Viñedos Singulares be combined with the current Rioja labelling rules on barrel-ageing.


    Rioja Quality Regulations

    The Rioja quality pyramid also now includes two other intermediate categories in addition to "viñedos singulars", i.e. "vino de zona" and "vino de municipio". The "vino de zona" are the classic Rioja Alavesa, Alta and Oriental, and "vino de municipio" is roughly equivalent to the French villages categories. As the borders for zones and "municipios" are political rather than natural, the denominations can still be used even if up to 15% of the grapes come from neighbouring areas.

    So we can see that whilst the four ageing classifications, namely Joven (young), Crianza (aged), Reserva, and Gran Reserva provide a quality guarantee, they do not link to a particular style. So these quality criteria based upon ageing remain intact, whilst the style of Rioja wines can evolve with the market.

    Sensory characteristics - the typicity of wine


    The next organoleptic characteristics for Rioja red wines, might be the most difficult to define and quantify, the "typicity" of the wine.

    Interestingly, the Rioja classification documentation mentions typicity, but does not define it, nor suggest its roles except as a "sensory characteristic". Wikipedia defines typicity as a term in wine tasting used to describe the degree to which a wine reflects its varietal origins and thus demonstrates the signature characteristics of the wine grape from which it was produced, e.g., how much a Rioja red wine "tastes like a Tempranillo wine coming from the Rioja wine growing region". Others extend this definition to include the terroir and the authenticity of a wine, i.e. soil, climate, grape varieties, the history and "the various know-how of a terroir" (which I guess this includes the uniqueness of the vineyard management and winemaking expertise). So is it about the unique taste of Tempranillo grapes coming from the Rioja? Or is it all about authenticity, i.e. the mix of geographic origin, the grapes used, winemaking techniques, the year, the taste, etc.? One writer defined typicity as "simply" being about the similarities and differences between two different wines. Another saw typicity as making it possible to differentiate, identify, and recognise a particular wine in a group of similar wines. The problem today is that making wine is increasingly based upon chemistry, and the skills needed are available in most parts of the world. So is typicity, which describes a certain grape grown in a specific region and subject to specific winemaking techniques in that same region, really about what is genuine and what is a copy or a fake?

    Whatever method used to define or analyse
    typicity, there are still other questions that need answers. Tempranillo is grown all over Spain, and in Portugal, the US, Argentina, Chile, Mexico and Australia, so is the varietal typicity of Tempranillo specific to Rioja, or to Spain, or does it show the same characteristics as Tempranillo grown in Chile or Australia? Which of those Tempranillo's reveal the true identity of the grape variety? In which climate or terroir does Tempranillo thrive better? Which of those regions is most typical or atypical? In the Rioja region some producers prefer not to work within the boundaries of the Rioja appellation system. Their wines may not be typical but nevertheless they may still show typicity of the Rioja terroir and viticultural practices. And the final question, looking forward 50 years, what will be the impact of climate change on the typicity of Rioja wines?

    Descriptive sensory methods are commonly used for the sensory analysis of wines, and are used to characterise sensory differences between products after a first step of discriminative tests to highlight differences. These descriptive methods may use qualitative and/or quantitative approaches, and comprise a multitude of standardised tests developed in the food and drinks industry.

    All these tests have been adapted from the conventional descriptive analysis, also called the Conventional Sensory Profile, in line ISO 11035:1994. This test was based on the variation in individual perceptions with stimuli concentration. One problem is that tasting panels need to be trained to apply an independent intensity scale to the sensory analysis of a complex matrix of options, which is usually too time consuming. According to the norms of the conventional profile, a sensory test takes approximately 120 hours, including vocabulary generation, training and the evaluation of training, before the sensory evaluation can be performed (according to ISO 13299:2016). This is unworkable in practice, so many
    wineries have turned to a sensory profile specific to a wine, and with only one variable, e.g. changing sulphur dioxide levels.

    The "Just About Right" methodology (JAR) is a direct approach to measure the deviation from ideal levels per attribute. With JAR, assessors directly assess deviations from ideal, usually in terms of labelled scales with the end points "too weak" to "too strong’", and the midpoint of the scale labelled as "just about right". This is a direct measure of the perceived attribute intensities, but it does not directly quantify them. JAR is usually expressed as the percentage of respondents who consider the attribute level as too high, too low, and just about right. Also, with JAR, overall liking is collected and deviations from the ideal can be related through penalty analysis, i.e. a way to identify potential directions for product improvement in order to go towards "liking" or typicality data. Surveys can be used to evaluate consumer expectations concerning a brand name, the origin of the wine, or
    grape variety, and establish a practical meaning to the concept of terroir. Tests can be performed to assess the consumers (and winemakers) ability to discriminate between different wines in terms of typicality, i.e. based on dominance of some sensory descriptors. At the same time biochemical characteristics commonly used to assess wine quality were also determined: e.g. alcohol level, acidity, pH, total phenols, colour parameters, spectrophotometric parameters and CIELab parameters.

    In addition, although not mentioned the
    Rioja classification documentation, there is a laboratory technique available for fingerprinting a wine. In fact, infrared spectroscopy (FT-IR) not only can detect and quantify key wine compounds, but it can also be used to classify wines and monitor their fermentation or ageing process. One problem is that although anthocyanins and tannins present in skins, must, etc. can be assayed, direct correlations between analytical parameters and the wines produced are not always easy to find. On the other hand there are some valuable correlations already available, e.g. between CIE L*a*b* colour parameters for grape hue and colour intensity and the phenolic characteristics of wines. This kind of analysis can be used, along with traditional measurements of technological variables (i.e. sugars, acidity, pH), to determine a harvest date.

    ?
    Wine encapsulates the expression of multiple inputs - from the vineyard location and environment to viticultural and
    winemaking practices - collectively known as terroir. Each of these inputs influence a wine's chemical composition and sensory traits, which vary depending on cultivar as well as provenance. These aspects underpin the overall concept of wine typicity, an important notion that enables wine from a delimited geographical area to be differentiated and recognizable in national and international wine markets. Indeed, consumers are increasingly more aware of the significance of regionality and may use this to influence their purchasing decisions. Understanding which sensory attributes represent regional typicity and how these are best conveyed to consumers is therefore important for the prosperity and reputation of producers. As reviewed herein, the sensory typicity of wine can be identified using different types of testing methods, with the most effective being a combination of approaches, such as sorting task in combination with descriptive sensory analysis. Consumer perceptions of regionality and wine typicity are then examined to provide insight into their behaviors. This includes consideration of the importance of origin to perceptions of quality and typicity, in terms of meeting expectations and engaging consumers. Based on the literature reviewed, it is proposed that wine typicity can be defined as a juxtaposition of unique traits that define a class of wines having common aspects of terroir involving biophysical and human dimensions that make the wines recognizable, and in theory, unable to be replicated in another territory.







    Specific Vinification Practices and Imposed Restrictions


    Growing practices


    Vineyards are considered to be producing Rioja grapes provided three or more years have elapsed since planting and the vines have attained their fourth growth cycle. Planting means the final placement of vine plants, grafted with an authorised grape variety, with a view to produce grapes.

    Perennial fruiting plants such as
    vines are fairly quick to establish and usually start fruiting sooner than fruit trees. However it can take a full three years to get from the initial planting of a brand-new grapevine through the first harvest, and the first vintage might not be bottled for another two years after that.

    The starting point is to
    assess the soil and climate and choose the right vines for each site in a new vineyard. In the Rioja there are strict rules concerning where a vineyard can be established, and what are the allowed varieties of grapes. In addition, decisions will be needed about the row orientation, how to space and trellis the vines, and how to treat the soil, if necessary.

    Minimum Site Requirements for the Planting of
    Vitis vinifera:-
    • Frost free season exceeding 150 days

    • Minimum mid-summer temperatures no lower than minus 25°C

    • Minimum temperatures during the shoulder months of November and March no lower than -20°C (-10°C to -15°C may cause damage at this time depending on the dormancy stage of the plant)

    • A minimum of 1200 growing-degree-days with temperatures greater than 10°C are needed to mature the fruit for a Bordeaux-type red wine grape

    • Well drained soils

    • Sunshine between April 1 and October 31 to exceed 1250 hours


    Key questions are as follows:-
    • Soil - Vine health and productivity is dependent on a healthy root system. Roots operate most effectively in neutral, deep, well drained, and well-aerated soil with good organic matter and an adequate supply of nutrients. Grape vines are deep rooted plants requiring adequate soil depth and are not suited to shallow soils. Often areas of poor vine vigour can be traced back to poor underground soil conditions.

    • Temperature - Is it a costal or inland site? Are the summers hot and dry? Grapes grow best under mild, dry spring weather conditions, followed by long, warm dry summers after bloom. Cold temperatures and rainfall during the flowering period may interfere with fruit set.

    • Rain - What are the rain and moisture patterns over a typical year? Significant amounts of rainfall during the growing season can have an adverse effect upon disease development and grape quality. Rain and wet weather at any time can be conducive to the growth of pathogens detrimental to crop production and vine health. Rain at harvest may also reduce fruit quality. The advantages or disadvantages of rain depends on when, how long and how much it rains.

    • Frost - Are there likely to be problems with cold air or frost? Frost during the winter can penetrate soils to a depth of about 50 cm, and may damage or even kill vines. Cold air flows down slopes and collects at the base creating frost pockets and areas with late spring frost and early fall frost.

    • Sunlight - How long is the growing season? What would be the average number of growing degree days per year? Radiation from the sun has an effect on air and soil temperature, transpiration, soil moisture, atmospheric humidity, and all plant processes such as photosynthesis, cell division and flowering. It also affects sugar accumulation, bud fertility, wood maturity, and crop yield and quality. Growing degree days is an expression of the amount of heat a vine receives above the basal development temperature. One growing degree day is accumulated for each degree the mean daily temperature is above 10°C. Each day is added to previous days to give the total growing degree days accumulated over a season.

    • Elevation - Grapes can be grown over a wide range of elevations, however there are limits above which grapes can not be grown economically. Increases in elevation of 100 meters may reduce the average annual temperature by as much as 1°C. Vineyards at higher elevations are therefore generally cooler than vineyards at lower elevations in the same region. Higher elevations are generally wetter due to increased precipitation during the growing season and winter months. Cooler temperatures at higher elevations delay bud break, flowering and ripening dates. The list of varieties suitable for viticulture at higher elevations becomes shorter and more restrictive.

    • Slope - The amount of heat accumulated at a site varies depending on the slope of the land and the direction of the slope. South facing slopes are the best choice, and total accumulated heat units are generally greatest near the mid-slope, less on hilltops and lowest near the base of the slope. Exposed hilltops have lower maximum temperatures and slightly cooler minimum temperatures than mid-slopes. The angle of the slope, in relation to the location of the sun, is very important to maximise the amount of solar radiation collected at a site. Gentle slopes are the best because they provide good air flow and drainage, and maximises heat accumulation.

    • Wind - Moderate air flow is beneficial to grapevines as it generally results in reduced disease. However, significant winds can cause serious damage to grapevines, and have a negative effects on vine growth, production and fruit quality. Vines create a special climate between the rows and in the leaf canopy that is altered or destroyed by winds. Exposure to moderate and high winds has a desiccating effect due to the high evapotranspiration rates, which causes physical damage. High winds often result in tattered leaves, smaller leaves, broken shoots, extensive lateral growth, shorter and fewer shoots, and smaller clusters. Winds in excess of 12 km/h cause stomata to close, resulting in reduced photosynthesis. In the winter, wind can remove snow cover which may increase the risk of soil drying and root desiccation. In regions with significant wind issues, row direction should run parallel to the prevailing wind where possible in order to reduce shoot damage. Sheltered vines protected by artificial or natural windbreaks have higher percentages of bud break, more shoots, higher pruning weights, larger clusters and more berries per cluster, lower pH, and potassium.

    • Sea or Lakes - Large bodies of water moderate temperature effects on the surrounding areas. They have a large heat storage capability which has a cooling effect in the summer and warms the surrounding area in the winter. In addition to this moderating effect, vineyards located on slopes close to large lakes, rivers or the sea, benefit from the reflection of solar radiation from the water surface increasing the length of the frost-free period. Lakes, large rivers or the sea, can also increase the surrounding area humidity and cloud cover. All of these factors reduce the risk of late spring or early fall frosts and extend the growing season.

    • Row Direction - Rows should be planted north-south if the slope of the site allows. This allows for the canopy to maximise the amount of solar radiation it intercepts. The fruit on the east and west sides of the canopy will develop at the same rate, increasing the vineyard uniformity and quality. East-west row orientation exposes the southern facing fruit to more heat and sunlight which results in uneven development between the north and south sides of the canopy. In areas with very high wind speeds the row orientation should be parallel to the wind in order to minimise damage to the canopy. In areas with a high frost risk the rows should run parallel with the slope to increase air drainage.

    • Vine Spacing - The decision on plant density should be determined by how well the vine’s roots will exploit the soil. There is little evidence to suggest a higher density results in a higher quality wine. However, the higher densities do allow for a lower yield per plant to achieve production goals and this could offer a greater chance of survival from a severe winter. Vineyard establishment costs, as far as vine spacing is concerned, are influenced more by the number of rows per hectare than by the number of vines per hectare. Between-vine spacing in the row should be designed to spread the wood of a vine on a trellis in such a way that the vines produce the desired yield without crowding. The pruning system (cane or spur) that will be used will influence the in-row spacing. Cane pruned vines will need room for 12 to 14 bud canes when laid along the wire, with 10 cm between cane ends to prevent shoot and fruit crowding. Cordons with spur pruning do not need as much space on the wire. The most common distance between rows is about 240 cm, with a vine spacing of about 120 cm.


    A vine can be grown from
    a single grape seed. Seeds can be collected from the bottom of the fermentation tank during winemaking, because they are not harmed by fermentation. Seeds can also be collected simply by cutting mature grapes open and removing the "pips". Firstly, the seeds need to be put in water and only those that sink should be kept. Next, the remaining seeds should be placed in a Ziploc bag with a very small amount of moist peat, and left in a fridge. Three months at around 4°C is enough to "stratify" grape seeds. The seeds can then be potted and, if kept at between 18°C and 24°C, they will germinate in one to four weeks. Later they can be replanted in a nursery, and the following year replanted in test rows (a one wire trellis). Below we can see some vines that have been nicely trained on trellises for one year.

    One Year Old on Trellises


    Even though most commercial vines are
    self-pollinating, grapes have a lot of variation in their genes. Plant a thousand seeds and none of the seedlings will be exactly like the original variety. But if a variety has no resistance to powdery mildew, the seedlings are unlikely to have any either. However, if a grape has some resistance to mildew, it’s possible that a seedling could inherit a new combination of genes and wind up with greater resistance. Also, for many traits it’s possible that there may be hidden "recessive" genes that will appear spontaneously. More than a few traits are reshuffled in the seedlings, so dozens are recombined in any one offspring. This means an improvement in one trait might be offset by a weakness in another. To beat the odds, it is usually necessary to grow a lot of seedlings to find a few that have all the positive traits. There is no set number, but 1,000 seedlings is a good baseline. About half the young vines will be subject to diseases or will grow too slowly, etc. Each of the remaining vines can be trained to produce one good cane. Some will not be self-pollinating, others will be eliminated after the first crop of grapes, and again after the first sample batch of wine made from each vine. About 1% of those original seeds will have the desired characteristics, but even then long-term consistency will not be guaranteed. Ten years of winemaking with a new vine is just barely enough to be sure it’s quality is consistent and it grows well in different conditions.

    Bleeding Bud Break

    In the Rioja, "bud break" (or "bud burst") can begin in mid-March, and becomes widespread by the end of March. In fact, in 2020 the bud break in Rioja was on the 10 April, and the rain in April and early May boosting the rapid growth of the plants. The start is signalled by a "bleeding" of the vine, meaning that the sap has started to flow. Bleeding is mainly sugar coming out of the cuts made during pruning, and signals that cellular activity has started again after the winter dormancy. The first buds can grow by 1 cm to 4 cm per day, and in May the vines can start to bloom. Grape petals are green, and unopened buds are often mistaken for small green grapes.

    The period from bud break to flowering is very temperature-dependent, and low night temperatures can damage the tender shoots, especially once the buds start to swell into flowers. The
    flowering stage starts about a month after bud break. Grape vines have "perfect flowers" and are self-pollinating, but pollen release and dispersion is better in dry weather, with rain and strong winds reducing pollen density. The initial inflorescence contains hundreds of flowers, but not all flowers will turn into berries.

    Bud Break and Pruning

    Canes grow new shoots, which will later turn into new leaves, and mature vines need to be pruned to promote the right balance between the number of shoots and the number of buds which will produce grape clusters. Too many shoots and not enough buds means that the vines will have too many leaves shading the fruit, making it hard for the clusters to ripen. Too many buds and too few shoots produce a similar problem, i.e. so much fruit that none of it will ripen properly. Poorly pruned vines can't produce high-quality fruit, and winemakers can’t make high-quality wine.

    Many vineyards will try to remove weeds and
    till and aerate the land in order to avoid the unwanted presence of insects which may harm the vines. In the Rioja with the rain in April and early May 2020, it was important to trim the vines to improve exposure and ventilation through the canopy. With the higher than average rainfall and higher temperatures, growers had to also check for the possible appearance of mould.

    Vine Flowers

    In mid-June 2020 the fruit setting became widespread, i.e. when the fertilised flower began to develop a seed and grape berry to protect the seed. Each flower can "set" and become a single grape, however in most varieties only about 20% of the flowers set, at most. This is a positive, because the grapes would otherwise be so tightly packed that mature clusters would hold too many crushed and split grapes. The weather conditions during fruit set determine not only the yield but also the quality.

    Many winemakers stress the mantra that "
    wine is made in the vineyard". The key is that growing grapes for wine is non-intuitive. The economics of a winery is based upon the fact that fewer grapes means better quality grapes, which means a better quality wine that can be sold for a higher price.

    Setting

    In the Rioja zones which had been most affected by the rain during flowering, setting was less and looser, more open berry clusters were formed (as seen above). At the end of June 2020 veraison had started throughout the Rioja growing region, taking place quite quickly due to the hotter summer temperatures. Veraison can be seen as the change in colour of the grape berry, which indicates the transition from berry growth to ripening.

    Veraison


    The high temperatures in 2020 accelerated the build up of
    sugars in the grapes and lowered the acidity levels. A few weeks later, after the September rains, the grapes reached a "point of balance", so that picking was widespread by the end of the month. With the threat of a wet October looming, as well as the second wave of Covid-19, the harvest was one of the shortest recorded.

    It's important to realise that growing conditions will vary in the three official
    Rioja growing zones, namely Rioja Alta, Rioja Oriental and Rioja Alavesa.

    Rioja Alta is the coolest zone, and in 2020 conditions were wet but hot during the summer months, leading to a degree of stress for the vines. However, that helped to block the development of fungal diseases and ensured optimum ripening. Precipitation was spread over the whole year but rainfall was especially heavy in the spring and there were also cases of torrential rain and hailstorms. In general the winter of 2019-20 had been mild, but spring was hot, favouring the start of the cycle of weeping and bud break. The average temperature for the whole month of May was over 15ºC, which translated to midday temperatures of almost 30ºC. At this point in the cycle, the evolution of the vines was up to 10 days ahead of its usual schedule. The summer began with mild temperatures until mid-July, then until the end of August every day saw temperatures rise above 30ºC. Generalised harvesting began by 25 September, just a few days earlier than in a typical year.

    Rioja Oriental is the sub-zone with the greatest Mediterranean influence, and "bud break" began in mid-March, becoming widespread at the end of March. The main challenge was managing the high rainfall and the unusually high moisture levels, especially for growers following organic methods. In the winter, temperatures rarely fell below zero, and a hot summer brought high temperatures, and maximums of 35ºC on several days during July and August 2020. This led to a marked acceleration in ripening and the first grapes from early-ripening varieties were picked in mid-August. By mid-September, with diurnal temperature differences of up to 20ºC in the vineyards, vines were able to mature with no stress and reach the optimum point of ripeness at the right time.

    Temperature in the
    Rioja Alavesa more or less followed those in Rioja Alta, but rainfall followed that registered in the Rioja Oriental. The result was a greater variation in acidity levels and anthocyanins in the Rioja Alavesa wines.

    The DOCa Rioja Control Board awarded the rating of 'Very Good' to the 2020 vintage.


    A very important topic in terms of growing practices is
    grafting. Grafting is the process of adding a scion (a grafting) to a rootstock to produce a new grape vine. This practice in modern viticulture was discovered in the 19th century to be the best defence against phylloxera.

    Phylloxera was one of several diseases that came from America and almost destroyed Europe's vineyards. The long trip from the Americas to Europe meant that the lice died during the voyage, but when the trip was shortened with steamships, the eggs survived, and the pest slowly crawled its way through Europe devastating every vineyard in its path.

    Phylloxera first "landed" in London, then appeared in France in 1863, but would only arrive in the Rioja wine growing region in 1899. It was in 1887 that French scientists finally discovered that they could graft French vines (
    vitis vinifera) onto American rootstock (specifically vitis labrusca) and save their plants.

    Today, most plants are grafted throughout the world specifically to prevent phylloxera. A North American vine species (
    vitis labrusca, vitis riparia and especially vitis rupestris) is used for the bottom vine (or rootstock) and the higher quality European species (vitis vinifera) is grafted on top (the scion). This is because North American vine species form scabs over the feeding areas of the phylloxera louse and prevent the vine from dying. In fact the louse sucks the juice out of vine roots and thereby destroys the vine through lack of nutrients. American vines were stronger and more resistant, but did not produce grapes of wine quality. Grafting, a technique known since ancient times, was the solution.

    Vitis rupestris - is a species whose native soils are gravels and banks of mountain streams. It has a strong vertical root system. It is somewhat drought resistant and has a long vegetative cycle and matures late. It is tolerant to some lime conditions.
    Vitis riparia - is found on river banks, islands or upland ravines. It is fond of water, but does not grow in swamps. It likes rich soils, but not lime (but is still more tolerant of lime than rupestris). Riparia has a short vegetative cycle and ripens early. It has excellent cold resistance, but it has low vigour.
    Vitis labrusca

    Nowadays, the grafting business is fully evolved. Viticulturalists will choose various rootstocks for soil suitability, frost prevention or to control vine vigour, and they can order fully grafted vines from vine nurseries (the unit cost for 35 cm high, bare root grafted Tempranillo is <€20). However, my understanding is that estates such as the Marques de Riscal apply their own field-grafting technique.

    ——
    Today we tell you about a millenary wine growing practice that continues to this day besides the new technologies, the "acodo" layering; also known as "mugrón" or "morgón" in areas of La Rioja.

    The vine plant, as a living being, has its life cycle and this sooner or later will come to an end. The layering, frequently used during the phylloxera period, is carried out for the substitution of death vines also called "faltas" and it consists in bending down to touch a hole dug in the ground (where the death vine was) at about 25 cm depth, a long-growing stem left from the past year and cover it with soil and some weight. Then the extreme will be pinned in place, the buried part of the stem will grow new roots and will become a new vine plant, that will be fed by its own roots and by the ones of its progenitor and as in all vegetative propagation will be a clone of the original.

    https://en.wikipedia.org/wiki/Vine_training
    https://en.wikipedia.org/wiki/Basal_shoot








    Growing practices - planting density


    Minimum planting density is 2,850 vines per hectare, maximum planting density is 10,000 vines per hectare.

    A question often asked is
    how many grapes are in a bottle of wine? It's a simple question that has no simple answer. It depends upon the grape variety, soil type, planting location, etc. But starting with the idea that there are about 70 to 100 grapes on a cluster. A mature vine can produce about 40 clusters, if nothing is done to limit its yield. This could mean that a vine could produce up to 10 bottles of wine (i.e. 400 grapes for one bottle). Nobody thinks of yields in this way, but yield per hectare is more credible. In Europe it was reported that yields could range from 35 to 400 hectolitres/hectare, remembering the lower the yield, the higher the quality of the wine. One estimate was 70 grapes/cluster, and 5 cluster per bottle, another was 130 grapes/cluster and 9 cluster per bottle. Some winemakers went for an average of about 700-750 berries per bottle, plus or minus 100.

    It's a bit of a fools game, but a nice glass of wine might be about 1 cluster of berries.

    So what is
    planting density, beyond just the number of vines per hectare? Planting density is one of fundamental aspects of vineyard planning since it impacts on vine density, and thus on vineyard profitability throughout the entire life of the crop. However, even on this simple criteria information is contradictory. One source mentioned that the "standard density for traditional European viticulture is 10,000 vines/ha", but densities of less than 600 vines/ha were mentioned, as were experimental densities of 40,000 vines/ha. But another source noted that in hot regions, where competition for water is particularly high, planting density can drop to 2,000 vines/ha, and that the most frequently planting density is between 3,000 and 6,000 vines/ha.

    Planting density is not the same thing as
    yield. In Europe yields are often expressed in hectolitres/hectare (hl/ha), or eventually tons of fruit/hectare (t/ha). The lowest is often mentioned as Yquem, with a 9 hl/ha, or the equivalent of one glass of wine per vine, but a respectable average might be 50 to 60 hl/ha for quality wines.

    And neither planting density not
    yield are directly linked to value. At least according to some experts one metric tonne of picked grapes can range in value from as little as about €140 through to nearly €50,000, with the average in Spain being about €500/tonne.

    Planting density translates into
    distance between rows and distance between vines. Before discussing rows, it is just as important to decided on the direction of the rows, which will depend on the slope of land, the need for optimal light exposure, and wind (remembering that good airflow through the canopy helps control fungal diseases). In the past the distance between rows was often determined by the width of the tractors, sprayers and tillers available at that time, however today there is a broad selection of equipment that can fit into a row width of as little as one metre. Row spacing is now more likely to depend upon the training and trellising system used (as well as the trellis height), with a distance of three metres between rows being a common compromise. Obviously another key consideration is canopy width and avoiding wide rows where sunlight will be "lost" to the vineyard floor.

    Vine spacing in a row was traditionally determined by the vine size and vegetative vigour of the particular cultivar, and the target was to optimise the number of buds per unit area of land. It would appear that in France and the US a vine spacing of about 250 cm is practiced. Yields will increase up to the point where shoot crowding and shading begins to reduce the juice quality. There are a multitude of variables in play, ranging from the number of tractor turns through to the increased cost in spraying more widely spaced vines for pest control. If irrigation is used, then costs will again vary for drip or sprinkler irrigation. Another way to look at vine spacing is to look at buds per vine. Small vine spacings will require few buds per vine for the same yield per unit surface area, and reducing the crop load per vine will, all other things being equal, produce less, but riper fruit. And yet another important parameter impacting vine spacing is the potential of the soil in terms of fertility and its water holding capacity (which of course will vary as a function of the grape variety, e.g. root depth, etc.). Vine spacing is all about the fine details, e.g. a particular variety/rootstock combination might be more vigorous and produce more buds (risk of shoot crowding) and leaf coverage (risk of excessive shading) and might therefore be best planted further apart. However, planting these vines nearer together might increase competition between vines for water and nutrients, thus reducing their vigour. The vines will be forced to send their roots deeper rather than grow laterally, improving the interaction between vine and soil (i.e. terroir) and increasing their resistance to water stress. So it's all about balancing vine density, soil potential, and the inherent vigour of the cultivar and rootstock, not forgetting other less obvious parameters such as canopy height, allowable pruning options, etc. It is worth repeating that producing wine is intuitively contradictory. Higher density planting leads to lower grape production per vine and smaller grapes which are, however, of superior quality. This is because the timely slowing and arrest of vegetative activities in the phase leading to véraison works to increase the accumulation of sugars and tannins in the bunch resulting in greater alcohol content and better wine structure and colour.

    One study involved rain fed,
    trellised Tempranillo, pruned to 10 buds per linear metre, and 2 bud spurs. With a constant width of 240 cm between rows, vine spacing varied between 100 cm, 140 cm, and 180 cm. Over a five year period they found that grape yield (+7%), cluster weight (+5%), and berries per cluster (+5%) was superior for the 140 cm spacing. Berry weight, total soluble solids, sugar concentrations, pH, titratable acidity, and total polyphenol index did not significantly change. The key different appeared to be linked directly to the weight of berry clusters, and therefore a 140 cm vine spacing was the optimum in terms of production and economics.

    Hidden within planting density are a number of other important topics, albeit less evident, all aimed at better managing vineyards to product better and more profitable wine.
    One topic is
    yield forecasting, which traditionally involves using score sheets to determine vigour, leaf status, exposed leaf area, canopy porosity, fruit exposure, etc. all linked to the final grape and wine composition and quality. These techniques are somewhat imprecise, time consuming and expensive. Now image processing can be used for disease detection, smart spraying efficiency, colour classification and yield estimation.

    Another important aspect of planting density concerns the essential role of
    solar radiation in plant photosynthesis (this is the so-called "photosynthetically active radiation" in the wavelength range 400-700 nm). Ultraviolet (UV) solar radiation on the vines is needed for the production of certain important chemical compounds that are directly related to yield and wine quality, and in addition, UV-B (280-320 nm) can affect plant-disease interaction, affecting both pathogens and the host. Plant photosynthesis is affected by vine variety, planting density (row and vine spacing), trellis height, pruning, etc. However, the important point is that in addition to the direct solar light component, we now know that the diffused solar light component significantly contributes to plant efficiency under shaded conditions. And given that UV-B is more highly diffused than other components of solar radiation, we now know that plants have a specific UV-B photoreceptor that influences plant growth and development, activates plant-defence mechanisms, and thus can reduce disease and pest incidence. An interesting aside concerning UV-B is the effect of a projected increase due to global warming. It was found that Tempranillo vines did suffer physically from an increase in UV-B, but that it was modest and did not affect their photosynthetic performance.

    Increasingly agricultural robots (i.e mobile robotics machines) are being used in the field of
    precision viniculture. Agricultural ground robots can acquire large amounts of data, but the performance of their non-invasive sensors will be affected by planting density. There are a number of different robots that assess canopy nitrogen status, berry anthocyanins, canopy density, leaf temperature, fruit health, leaf transpiration, vine water status, and yield estimation. Pruning weight is an important indicator of biomass reduction, carbon storage, and vigour, and is particularly sensitive to soil fertility and water availability. The Ravaz Index is the ratio between pruning weight and vine yield, and is an indicator of grape quality. Computer vision, used with ground robots and sensors, is used for the evaluation of berry and cluster characteristics, number of flowers per inflorescence, canopy architecture, grapevine phenotypic, and yield prediction. And it can also be used to assess vine pruning weight, even if industrial applications are still not routinely used. The idea is to determine cane number and diameter, and thus derive total pruning weight. Their usefulness depends on being able to deal with shoots that are also inclined, and of course it all depends the form of the vine and on row and vine spacing.

    Pruning Wood Assesment

    (A) is the image of the vine at night, and (B) is the segmented image of the pruning wood using image analysis. The blue pixels correspond to pruning wood, brown is the truck and cordon, and the red rectangular is the region of interest.
    Below is a map of the pruning wood weight for a Tempranillo commercial vineyard in the Rioja. Brown is low vigour and green is high vigour.

    Map of Pruning Wood Weight

    The statement that the minimum planting density is 2,850 vines per hectare, may appear a little academic, but the Rioja control board has in the passed clearly indicated that failure to meet this requirement would mean that the vineyard would be rejected and would not be registered in the DOCa Rioja Regulations. Calculating this lower limit just means dividing the number of vines by the row and vine spacing, i.e. 10,000 vines with a row spacing of 280 cm and vine spacing on 120 cm would yield 2,976 vines/ha (accepted), but with 10,000 vines and a row spacing of 300 cm and vine spacing on 120 cm would yield 2,777 vines/ha, and would be rejected.
    However, it would appear that a certain flexility did exist for older vineyards, e.g. one famous 45-year-old Rioja winery clearly states that its planting density is 2,800 vines/ha. Many of the better know Rioja
    wineries appear to operate in the range 2,800 to 3,000 vines/ha, and the regulatory maximum of 10,000 vines/ha appears to be very unlikely.

    Growing practices - pruning/training systems


    Permitted
    vine training and pruning systems are as follows:-
    • Traditional bush or gobelet and its variants.

    • Double cordon.

    • Rod and spur.

    • Single or unilateral cordon

    • Double Guyot is exclusively for white varieties.


    All red varieties are pruned to a maximum 12 buds per vine, except for
    Garnacha where 14 buds are allowed.

    In the winter months, with the low temperatures, the
    vegetative cycle stops and the vines have a chance to recover and stock up on reserves in their trunk and roots. Pruning helps vines complete their essential hibernation process. It consists of cutting all leafless shoots to prepare the vine for the ensuing budding period. Controlling the grape yield improves the quality, and strengthens and extends the vines productive life. In the case of younger plants, pruning is also used to train the vine in the shape desired by the viticulturist.

    Primitive Secateurs

    Pruning knives have been around for centuries, but to cut shoots with a fast and clean blow requires experience, patience and a good deal of energy. Secateurs made the process much more efficient, since they distribute the force better and, above all, make the pruning more accurate. The first ones used by grape growers at the end of the 19th century were similar to those in the picture above. One of the two opposite blades had a kind of axe on the back, which allowed the small knots of the vine shoot to be cut in the “old-fashioned” style. So this tool represented the transition between a pruning knife and modern secateurs.

    Goblet Trained

    Historically, the free training or goblet system (as above) is the most widely used system in Spain and throughout the Mediterranean basin. The most common alternative is the trellis system (with the unilateral or single cordon, or the bilateral cordon as seen below), in which vines are trained vertically using wires strung between posts.

    Cordon Trained


    At least one report on
    Rioja wines mentioned that older vines were bush or goblet trained and spur pruned. The alternative is where the younger, more productive vines are trellised and cane pruned (or Guyot trained). Trellises allow machine pre-pruning and make many of the vineyard routines easier.

    Another form of
    pruning is "espergura" (best translation de-suckering) which is vine green pruning, or the removal of branches that would otherwise create a mass of leaves and prevent entry of air and light into the plant. In particular this involves the removal of long sterile stems from the trunk, which would otherwise not provide grape clusters and would weaken the plant. Another aspect is to prune but avoiding too many cuts, since a cut is a major entry point for fungi.

    Even pruning is being affected by global warming with temperatures projected for the Rioja region to increase by as much as 2°C over the next 30-50 years. High temperatures during
    berry development can delay the onset of anthocyanin accumulation ultimately leading to lower levels at harvest. During berry maturation high temperatures can also cause inhibition of some key biosynthesis enzymes and even result in anthocyanin degradation. In addition, high temperatures can accelerate grapevine phenological stages leading to a decoupling of phenolic and technological maturities (i.e. sugar concentration, titratable acidity and pH of the grape juice). Whilst sugar accumulation becomes earlier and more rapid during a warmer period of the growing season, phenolic accumulation is inhibited and berry anthocyanin concentration may not reach an optimal level at harvest. The combination of high "total soluble solids" and low acidity can produce a high-alcohol, unbalanced wine.

    For an established vineyard, the negative effects of global warming on fruit maturation could be mitigated by adopting techniques that delay maturation, such as shoot trimming, post-veraison distal leaf removal, late winter pruning, double pruning, or so-called minimal pruning (MP). In traditional pruning, 85% to 90% of vine annual growth (dry
    canes) is removed, and six to eight two-bud spurs (approx. 12-16 buds/vine) are usually retained per vine. Minimal or light pruning is usually firstly carried out mechanically with a pre-pruner, and then any damaged spur tips are manually pruned and touched up. In light pruning, 10-12 longer spurs, with four buds per spur, were retained on each vine (approx. 40-48 buds/vine). Pruned wood is usually crushed, and then incorporated into the vineyards soil.

    In fact, in trials in the Rioja region it was shown that minimal
    pruning produce moderately higher yields and delayed berry development (as compared with severe trimming after fruit set and late pruning). Berries ripening correctly, and a higher anthocyanin concentration was found, probably due to smaller berries rather than an improved anthocyanin synthesis capacity. Minimal pruning also improves canopy light and vine health conditions by reducing vine vigour, and in addition it can save labour costs. Perhaps most importantly, minimal pruning delays maturation makes it effective in counteracting the impact of climate warming.


    The rules and regulations concerning
    pruning in the Rioja are very clear, and growers are constantly reminded that pruning work in vineyards must be completed within the dormancy period, before "bud break" (i.e. so-called green pruning). There does not appear to be any preference or advice concerning cane or spur pruning. The main difference is that spurs are short stubs with two or three buds each, whilst canes are longer, and typically have around 6 to 12 bids.

    However, the Rioja rules impost that a traditional bush or "
    en vaso" system and its variants (e.g. gobelet or goblet) must be pruned to a maximum load of only 12 buds per vine over a maximum of six spurs (i.e. spur pruning). This form of vine is frequently used where shading and fungal diseases are not such a problem and indeed protection from sunburn is useful. It doesn't need expensive posts and wires, but also can't be mechanised.

    The allowed alternative in Rioja is the
    espalier or trained pruning. The idea is that a thick healthy and fully lignified cane (i.e. brown and woody) is tied to a trellis wire. The objective of the pruning is to stop what is called "apical dominance", i.e. the very highest bud produces plant hormones to stop lower buds from growing, so the vine will try to get taller rather than grow side branches.
    One of the most popular
    training systems is the Guyot method, popularised by Charles Guyot in the 1860's. This is a head-trained system with a permanent main trunk, plus one cane and a spur for a single Guyot, or two canes and spurs, for the double Guyot. The canes are tied to trellis wires and then the buds on the cane grow into the vine's canopy and fruit for that year. Usually the canopy is then further trimmed and tied to trellis wires in a method known as "vertical shoot positioning". This allows good exposure of leaves to the sun for photosynthesis, and an evenly spread fruit zone close to the trellis. The canopy may even be topped or hedged by machine to keep leaf growth in check and help ensure good fruit ripeness. Pruning aims to ensure even "bud break" and growth along the cane.

    Spur and Cane Pruning

    What's the difference between the cordon system and the Guyot method? It's really more about cane (Guyot) and spur (cordon and "en vaso") training. In cane pruning the arms are pruned back, and the cane is the annual growth on which shoots will carry the fruit clusters. We can also see the renewal spurs which are shoots which are kept and will become canes the following year. In spur pruning the cordon (arms) are well established wood, from which spurs grow annually, and from the spurs there are the shoots and fruit clusters. Cordon systems usually consist of spurs where two or three buds are kept, and evenly spaced along the cordon. Both can be single or double, and there are numerous variations on the two basic forms. It would appear that the cane-based Guyot is favoured in cooler lower-vigour vineyards, and the cordon in warmer, more fertile locations able to support a slightly more vigorous growth. The goblet training is best suited to warmer, dryer vineyards.

    The Rioja rules require that in a double cordon system, the maximum load must not exceed 12 buds distributed over a maximum of six
    spurs.

    The Rioja rules also stipulate that for the
    cane and spur system the load will be distributed along a cane and one or two spurs with two buds with a maximum of 10 buds per vine.

    The
    Garnacha variety has a specific exception, where the maximum load can not exceed 14 buds per vine.

    Vinification Practices


    For red wines made with destemmed grapes, a minimum 95% of grapes should be Tempranillo, Grenache (Garnacha Tinta), Graciano, Mazuelo, and Maturana Tinta (Trousseau). For red wines made with whole grapes, this figure should be no less than 85%.

    Harvesting involves the collection grapes, and there are different ways to do this:-
    • Manual selection based upon visual inspection is the most traditional way. It is time consuming and not that precise, but is a fairly simple activity. This approach becomes more important, but more difficult, if the vineyard shows extensive berry damage, possible due to bad weather or infection, or both.

    • Manual picking of parts of a cluster of berries can involve the early removal of bunch tips if higher acidity and lower sugar content is desired.

    • Creating berry groups from different areas of the vineyard (for a particular harvest date). It is known that in a vineyards there will be different vigour zones. Low vigour zones will usually have a higher leaf area/yield ratio and lowest bunch and berry mass, whereas zones with the highest bunch and berry mass usually have the lowest leaf coverage. And as vigour and yields increases, must reducing sugars and phenolic traits decease.

    • Time-differential harvesting is about exploiting the fact that there are variabilities across a vineyard in terms of grape quality and ripening. So during the single harvest two different groups of grapes are picked, resulting in two different vinification processes. Why do this when it's possible to harvest on two different dates? The argument goes that leaving part of the vineyard to later can involve additional risks. First a change in the weather, and second, the possibility of a pest spreading. In addition, if the weather gets hotter it becomes more delicate to control the exact sugar accumulation, acidity, etc. in the remaining grape bunches, and fix on the date of the second harvest.


    Bunch Sorting Berry Sorting

    In addition to the selection in the vineyards, grape sorting is also carried out in the winery. Often two selection routines are adopted, i.e. first removing leaves, etc. and then after the destemmer, removing unripe, damaged, and rotten berries. Grape sorting after destemming has become increasingly important for premium wines. This type of sorting table often consists of a food-grade conveyor belt that lets the individual grapes spread out, making manual sorting easier. There are also optical sorters able to sort grapes by size, shape, and colour.

    Destemming is part of the first vinification phase, here grapes coming from vines are carried to the destemmer-crusher units that separate the stalks/stems from the grapes. Destemming is performed before the crushing phase and it’s very important because it removes a lot of water and tannins that are inside the stalks. The waste is usually recycled back to the vineyard as fertiliser.

    The working principle is very simple, grapes are loaded into the hopper and fall inside an holed stainless steel, or polyethylene, cylinder, where a beating shaft can detach grapes from stalks. The destemmed grapes are then sent to the crushing phase, that may be carried out in the same machine.

    Although destemming is a near-essential procedure in
    winemaking, the consequences must be understood. Stem mass can represent up to 30% to the volume to be processed, and if destemming is not performed a larger-volume press would be needed. Destemming raises the wine's alcohol content and total acidity (stems contain some water and very little sugar), but it noticeably reduces total polyphenols (by about 20%), and the hue of wine is slightly less red (although the resultant colour might be seen as slightly more intense). It is often argued that phenols derived from stems are more astringent and bitter than phenols derived from skin or seeds, so its good that they are removed.

    Destemmer-Crushers

    Nearly all commercial destemmers currently in use are horizontal rotating destemmers which have two basic components, namely the beater shaft and the rotating drum. The basic layout of a typical horizontal rotating destemmer can be seen above. Grapes are fed into the hopper at one end of the machine, the feeder being a variable-speed rotating corkscrew-shaped auger. The grapes pass through a rotating drum in which there is a beater shaft which runs along the centre of the rotating drum. The beater shaft is fitted with paddles which are arranged in a spiral around the shaft. The beater shaft not only feeds the bunches of grape into and through the rotating drum, but the paddles also beat the berries from the stems. The rotating drum has holes in it which act like a sieve, and it can be changed to adapt to the size of the grape variety. The berries can pass through the holes in the drum, but the stalks with the stems remain behind and are discharged at the other end of the drum. The aim is to remove the stalks and stems without tearing the grape. The berries then move through the crusher rollers where the skin is broken to release the juice. Depending on the manufacturer, the rotation of the drum and the beater shaft can either be in the same direction or in opposite directions. The ratio between the rotation speed of the drum and the beater shaft is usually fixed, but the rotation speed is usually adjustable on smaller machines to achieve optimum performance for each batch of grapes.

    Stalks and Stems

    Since the drum and the beater shaft are the two main components of a destemmer, the most important variations between destemmers involve these two components. Drums can vary in length, diameter, rotation speed and the direction of rotation, as well as hole size and shape (round or square). The size of the holes is of great importance and is usually chosen depending on the cultivar the machine would most often process.

    It's interesting to note that some of the earliest
    Rioja wines included the stalks and stems (and almost everything else) in the winemaking process, and the result was a thick wine with bits (and more) floating in it. Destemming was one of the processes imported from Bordeaux in the 19th century which led to a major improvement in the quality of the high-end Rioja wines (along with oak barrel ageing, etc.). So it's interesting to see today, people arguing in favour of whole-bunch fermentation (including the stalks and stems, etc.) because it is said to add a more savoury and less sweet character to the wine. One argument is that stems help break up the mass of skins and pulp, thereby affecting temperature and the movement of oxygen and carbon dioxide gases, meaning that whole-bunch fermentation is more regular throughout the tank because the liquid circulates more easily. That means the escaping carbon dioxide doesn’t produce such a thick "cap" of skins, and it also allows oxygen to permeate the fermentation to keep yeast active. Furthermore, the overall temperature tends to be lower so the process of extracting tannin and colour is more gentle. So some winemakers advocate for a proportion of whole bunches, and therefore stems, mixed with the otherwise destemmed fruit. This little detour is somewhat academic since whole-bunch processing appears not to have been used with Tempranillo, but it has been used with other varieties including for Grenache-based wines.

    Later in this report we will read that "
    the use of centrifugal crushers with a vertical shaft is also prohibited" by the Rioja Regulatory Council. This was a different design concept for destemming and crushing. In the past destemming was not as popular as it is now, and when performed it was more likely to occur after rather than before crushing. When motors replaced hand-power, one option was a vertical centrifugal crusher, and another was the horizontal centrifugal beater that both destemmed and crushed at the same time. These machines delivered high yields and high colour extraction, but also sometimes excessive tannin levels, and also occasionally imparted an excessive herbaceous taste to the wine. It must be said that there is a renewed interest in different and more intense crushing equipment because of the potential for enhanced colour extraction or reduced skin contact time in red wine production.

    Only grapes in good condition can be employed in the vinification of protected wines having a minimum natural potential alcoholic strength of 11% vol. for red grapes and 10.5% vol. for white grapes. Red and white grapes should be delivered separately for each partial delivery or weighing.

    Grape pickers are usually expert in picking bunches with grapes that look firm (with a soft/elastic texture), plump, are nicely attached to the stems (but with a low resistance to removal), and have a good, fully matured, colour.

    Not much is written about what constitutes "
    only grapes in good condition". Wikipedia has a list of grape diseases, and here are a few defects that can affect grape quality:-

    • Undersized/Oversized - Small grapes could be lacking in colour or sweetness, whist oversized grapes may have a lower alcohol concentration and a sour taste.

    • Colour Defects - Grapes can be green, red, yellow, purple, or even pink. The changing colour from green to amber is part of the maturing process of green grapes, but brown berries are a defect.

    • Skin Defects - Anything from cracks and scars, to discolouration or insect damage. A dull, wilted or flabby appearance can be the result of freezing injury.

    • Deformation/Shape Defects - There can be many reasons why a grape might have lost its plump or round shape, including pests (mite feeding damage), nutritional deficiencies, or toxicities.

    • Russet - Are distinctive rust-like coloured stripes on the fruit. Also, in addition to russeting being non-appetising, it can also affect grape quality control as it may be a sign of problematic environmental conditions or the result of mechanical damage.

    • Sunburn - Sunburned grapes can have a higher risk of browning or tasting bitter. In red grapes, sunburn is associated with decreased anthocyanin levels. Halos, bleaching, sunburn, and raisining represent degrees of berry damage due to oxidative stresses associated with high temperatures and high light intensity. Damage can be minimised by ensuring fruit is not exposed to prolonged, direct sunlight. At the same time, some sunlight exposure is essential for optimal wine grape quality, especially for colour in red varieties. The objective, then, is to expose clusters to intermittent or dappled sunlight through a discontinuous cover of a single leaf layer with gaps. In addition to controlling sunlight exposure, such a canopy allows cooling air movement into the fruit zone.

    • Stains - It’s not always easy to tell what causes stains on grapes with the naked eye. It could be the beginning of something more serious such as rot or fungus, or it could be caused by slight sunburn or russet. For this reason, in the case of stains, further grape testing should be done.

    • Pests - Birds, worms, or fungal damage is not uncommon in grape plants. Two examples are powdery mildew and sooty mould. If left to spread, these are dangerous for grape safety, and could quickly destroy a grape harvest or yield. Birds can peck at grapes, and the lesions can develop decay.

    • Insect Damage - One of the most common forms of insect damage on grape crops is the mealybug. This can come in the form of cottony egg clusters, eggs, or adults, and in some cases is a sign of the grapevine leafroll virus. The honey dew secreted by the mealybugs is an excellent medium for the growth of various moulds. Other common forms of insect damage are caused by beetles and moths, and some of these can be endemic. Whilst insects can cause damage, they can also be a vector for transmitting other diseases.

    • Bruising - Fresh berries are always going to be very susceptible to bruising. Bruising can be caused by hail.

    • Lenticel - These appear as small, freckle-like dots.

    • Split Berries - A split in a grape can happen when there is excess water. The cells inside the fruit expand to suit, however the skin of the grape is only elastic to some degree. This can happen naturally through rainfall, or as a result of excess irrigation.

    • Watery - Heavy pruning or a sparse grapevine can be two of the reasons why you might get watery grapes. Sometimes, if grapes are leaking water, they might appear cloudy or even mucus-like. Affected berries test low in sugar content and are thin skinned, can be easily broken and are liable to subsequent decay.

    • Open Wounds - Can develop during the growth process or as a result of mishandling during grape harvesting or grape picking. This can then cause problems such as water loss or pest infections like black mould.

    • Decay/Rot - Fungi can attack the fruit in various stages (e.g. powdery mildew, black rot, bird's-eye rot, bitter rot). This may develop, even after harvest, into decay. Sanitation treatments like fungicides can be helpful. Botrytis is a common form of bunch rot, and Cladosporium rot can occur if the harvest is delayed. Even small percentages of berries infected with these diseases can negatively impact the sensory characteristics of wines. Accordingly, the tolerance for diseased fruit is low.

    • Shatter or "coulure" - This occurs when berries fall from the stem (also known as dry fall). This can be caused from rough handling of the stem or tissue crush of the pedicel that leads to water loss and oxidation. Shatter can also be climatic and result from a lack of water or inner sugar migrating problems. Pollination-derived shatter (sometimes called "shot berries") can occur when the cluster’s berries fall before they have time to grow, or when the flowers of the grapevine are not pollinated properly.

    • Brown Berries - Grapes can have a wide range of colours, but when fruit starts to grow brown it's a negative, and it's important to discover why.

    • Scars - Scars can come from a variety of sources such as spray damage or mechanical damage (e.g. from left rub caused by wind). During scarring, berries can end up with tears, which are invitations for other rot and fungi, which can then easily spread throughout the crop.

    • Softness - Overripe grapes will cause the fruit to be soft to the touch, or develop mushy spots. On the vine, this means that grape picking was not done in a timely fashion, or that the fruit were not given sufficient nutrients. Soft or flabby grapes can also be the result of heat injury.

    • Mould - Mould is a common grape defect. One of the most likely examples is grey mould of grape, which looks exactly like it sounds and can quickly destroy a grape harvest. In general mould is an indication of decay. Black mould is caused by Aspergillus niger.

    • Cracks - Cracks can come from a wide variety of sources, whether it’s pests like powdery mildew or insects, or over- or under-irrigation. Once cracks appear, this can also invite additional problems. Soft berries are susceptible to cracking, especially late in the ripening period. Cracking has been associated with high humidity and rain, and often follows a period of severe water stress. Ensuring well-aerated fruit zones helps keep the humidity low and prompts drying following rains.


    Grape picking, is one of the key steps in ensuring "only grapes in good condition" go into the winemaking process. Pickers are mostly migrant workers from as far afield as South America, Africa, and Eastern Europe, but many also come from the nearest village. They usually remain on-site for anything up to a full 8-week grape-picking season (the season can start sometime in September, e.g. 13 September 2021 in the Rioja, and can go into November). For example, in 2015 the harvest actually closed on the 13 October, and a total of 441,000 tons of grapes were picked (and 15,000 tons of grapes were rejected). Most Rioja vineyards are quite small, and since the pickers only select ripe bunches, they might return several times to the same vineyard. Accommodation is provided, but it can be worse that rudimentary or reasonably civilised, with toilet facilities equipped with showers, a kitchen, laundry room, first-aid room and a dining room with TV. Each worker is expected to harvest well in excess of 1,000 kg of grapes per day, and they work non-stop, with days off only if it rains. The grapes are collected in small tubs or wicker baskets that can hold up to about 20 kg, but the better vineyards might only half-fill them so as to not damage the bunches during picking. In the old days the grapes were loaded into a "comporta", a kind of wooden vessel used to transport up to 100 kg or more. A day can be up to 14 hours, and the pay can be around € 7/hr. (or a little more experienced pickers). All the workers must have a contract and their papers in order, because police inspections and raids are routine. Most wineries work with agencies that supply labour, and ensure everyone has a contract, a permit and are legal, but there are always those who don't respect the rules. The grapes are weighed and the bunches inspected at the winery. At the sorting tables, unripe, rotten or botrytised grapes, and any remaining leaves are removed. In the better wineries there are two sorting tables, firstly a cluster sorting, then followed by a berry sorting. The second sorting is to remove any poor quality grapes and any remaining stems.

    Hand picking can be replaced by machines, particularly in the price-sensitive end of the market. These machines straddle the rows of trellises, blow air to remove unwanted leaves, etc., and beat the vines with rubber or fibreglass rods to shake or strip
    ripe berries from the stems (which usually remain on the vines). Some people might criticise the use of machines, but they work a 24 hr day (including during the cooler nights), and because they are anywhere between twice and five times faster than hand pickers the machine can pick the grapes at their optimum ripeness, thus preventing some crop loss. On the other hand the machines do cause more damage to vines and grapes, can't work on some steep slopes and narrow terraces, and might be an overkill for smaller vineyards. However, despite the machine costing €100k to €200k, hand picking can be two to three times more expensive, when factoring in wages, transport, accommodation and food. One of the requirements for Rioja's "viñedos singulares" is hand harvesting. In order to situate the two extremes, its worth noting that the average size of an Australian wine producer was already nearly 3,000 hectares in 1996, whereas still today more than 80% of the Rioja growing area is made up of vineyards that are less than two hectares. So what might be a good investment for one, might be ridiculously prohibitive for another.

    Picking and sorting is accompanied by a
    ripening control performed by the Rioja Consejo Regulador (Regulatory Council). In the final phase of the harvest cycle they carry out the ripening control of the grapes in order to provide all winegrowers with technical information on the most appropriate harvest dates in each location depending on the evolution of the vineyards. Samples are independently analysed for grape weight, probable alcoholic strength, total tartaric acidity, pH, malic acid, potassium, total polyphenol index, anthocyanins and colouring intensity.

    In the production of must the following traditional practices shall be applied, employing a modern technology, focusing on optimising wine quality. Appropriate pressures should be applied to extract the must or the wine and separate it from the pomace, so that the grape-to-wine ratio does not exceed 70 litres of wine per 100 kilograms of harvest.

    Making Red Wine

    So what are these "traditional practices"? Information on winemaking is as old as civilisation itself, and many different peoples have developed traditional practices typical of their lands and their place in history. However the basic procedures and techniques of the vinification process includes:-

    • Reception of raw materials - the ripening, harvest and transport of the grapes will largely determine the value of the wine to be produced. It is a crucial step in which the grape can begin to ferment, suffer breakage and be infected by unwanted organisms.

    • Destemming - consists of eliminating the stalks and stems. It reduces the astringency of the wine and increases its colour which is determined by the pigments in the grape skins.

    • Crushing - replaces the old "pisado" process, or treading under foot. Roller crushers were introduced in the early 19th century with the aim to crush open the grape skin without crushing the seeds (or stems at that time). The aim of this process is to separate the solid part of the grape, transfers the natural or endemic microorganisms to the must, and favour an aeration that starts the fermentation process.

    • Maceration - for red wines this process extracts pigments contained in the solid part of the grape after crushing. It is perhaps the most important difference between red and white wine production.

    • Addition of sulphur dioxide - in the form of potassium metabisulphite, a crystalline powder that generates sulphur dioxide in solution. Its antioxidant role and its effect on the growth of bacteria are key. Sulphur dioxide acts as a fungistatic in low concentrations and high pH, and a fungicide at high concentrations and in an acidic medium. Importantly its antibacterial activity affects first lactic acid bacteria and later acetic acid bacteria, but it can also affect the aroma and taste of the wine. An excessive concentration of sulphur dioxide will affect the malolactic fermentation that occurs after alcoholic fermentation. Even a normal dose will affect the course of fermentation, and a higher dose is a deliberate way to slow the development of endogenous yeasts, facilitating the implantation of preselected yeasts.

    • Transfer to a fermentation tank - for red wines, this tank consists of a so-called "cap" of skins floating on the must, which serves as a support for the yeasts.

    • Inoculation - low temperatures can limit the growth of endogenous yeasts. For this reason, it is important to force the start of fermentation with an external yeast inoculum that will be imposed on the indigenous yeast.

    • Alcoholic fermentation - a rapid multiplication of microorganisms occurs in the must. Alcoholic fermentation starting from the eighth or twelfth hour of cultivation when the temperature 25°C is reached (for red wine).

    • "Pumping over" - is the pumping of the must from the bottom to the top of the tank. The "cap" is "soaked", the mixture is homogenised and the medium is aerated.

    • "Racking" and pressing - emptying the fermentation tank and the remaining skins are pressed.

    • Malolactic fermentation - is a process that begins after alcoholic fermentation, and corrects the acidity produced. This fermentation is carried out by lactic acid bacteria and consists of the transformation of malic acid (with a herbaceous or "green" flavour) present in the wine to lactic acid (with a more pleasant taste and better aroma). It is not unusual for wineries to inoculate these bacteria to initiate malolactic fermentation.

    • Clarification - is the elimination of excessive levels of solids, thus guaranteeing the physicochemical stability of the wine. Suspended substances in the wine such as yeasts, bacteria and proteins are removed.

    • Crianza - ageing in oak barrels.


    So winemaking is not just about extracting and fermenting the juice from grapes. In fact it's the pulp, skins, and fibre that make up the grape, that provide the body, colour and unique flavour characteristics to the wine. Crushing simply breaks grape berries, allowing the juice, pulp, and seeds to mingle with the skins of the grapes. Pressing, on the other hand, is the process that separates the grape juice from the fibre and other solids that make up a berry.

    Crushing is performed before the fermentation, and the aim is to burst the skins so that all the inner solids can be exposed to the fermentation. Enough free-flowing juice will be released from the grapes to turn the crushed mix into a liquid called a wine must.
    It is common practice that the crusher hangs below the distemmer drum (as seen with the commercial destemmer shown above). The crusher is usually a pair of rubberised overlapping lobe rollers spinning at the same speed. There were numerous design variations, but the key issue is the ability to modulate the degree of crushing. There are different devices and techniques all aimed at a faster turnover during fermentation or the extraction of more colourful wines. One of the most well-established rapid extraction techniques is pre-fermentation heat treatment. The idea is to rapidly extract skin colour as compared to the slower extraction of
    tannins, in opposition to intense crushing which proportionally extracts more tannins than colour. However the rules applied to Rioja wines strictly prohibits both "unsuitable pressure levels" and "grape preheating or the heating of must or wine when in contact with pomace (i.e. solid remains of the grape) in order to extract colouring matter".

    The distinction between crushing and pressing is important since each plays a separate and important role in producing wine, and in our case red
    Rioja wine.

    Red Wine Vinification

    To understand better how grapes are turned into wine, we will try to insert short descriptions from different Rioja winemakers to highlight the variations in play.

    However, the first thing to note is that the majority of red grape varieties do not contain
    pigments within the pulp but rather in their skins. So an essential step in the red winemaking process is the extraction and transfer of these pigments, along with tannins and aromatic molecules, from the skins to the must during maceration. This means keeping the skins and the seeds in contact with the must in the tank during fermentation to extract and diffuse these phenolic compounds in the must, and to obtain the red colour provided by the skin's anthocyanins, as well as the antioxidant capacity and structure provided by the tannins. The tannins (proanthocyanidins, a class of polyphenols) extracted from the skins will have a strong influence on the barrel ageing capacity of the wine. The simultaneous maceration and fermentation processes make it necessary to balance the optimal conditions for both, which are quite different. Maceration and fermentation in red wines depend on several technological factors, including the design of fermentors to optimise both processes, with a key factor being the material used to build them.

    Temperature and "cap" management exerts a great influence on the extraction of phenolic compounds (anthocyanins and tannins), which then affects not only the structure, astringency, softness, and colour, but also the antioxidant capacity and the wines aptitude for ageing.

    Vat Fermenters
    Tank Fermenters

    Tanks for making red wines must allow the maceration of the skins (and possibly also the stems), and are sat on legs allowing the draining of pomace at the end of maceration. Some types of tanks have a diameter larger than their height, so that the caps are thiner and it's easier to "punch down" or "pump over" (tanks for white wine are usually taller and narrower). The tanks also have cone bottoms making it easier to remove the pomace after maceration. After 2-3 days fermentation, the production of carbon dioxide results in the skins floating to the surface, and this is known as the skin "cap".

    Maceration Cap

    Above we have an example of a skin "cap", left alone, the skins form a solid "cap" on the top of the juice. Bacteria would begin to ferment at the cap–air interface, and the result would be a volatile acidity problem, i.e. the wine would reek of vinegar, and be spoiled. Winemakers avoid this by keeping the cap moist, either by plunging it regularly, or keeping it submerged by a mechanical device, or by pumping juice over it.
    "
    Punching down" or plunging (below left), also known as pigeage, is the most traditional method, and can be done by machine, or by a special pole, or even by feet. This is typically done with shallow open-top fermenters. The idea is to break up the cap and submerging it in to the must, this is usually done between 1-3 times a day. Manual punchdowns are labour intensive and involve winery staff using a pigeage plate or fork to disrupt and submerge the cap by hand. Mechanical punchdowns use a similar plate attached to a hydraulic arm. Standard plate-on-pole punching is seen by many winemakers as a more aggressive extraction technique, since the plate is more likely (the fork less likely) to break, tear, and crush the skins, facilitating more extraction of flavour and colour (but much depends on how the technique is performed).
    "
    Pumping over" or remontage (below right), is potentially more disruptive, because it introduces more oxygen and the result can be a more intense style. It is more appropriate for bigger, closed fermentation vessels such as stainless steel tanks. "Pumpover" can be gentle or aggressive, and results depend upon a range of variables such as fermentation vessel, grape variety, ripeness, stem inclusion and fermentation length and temperature. Juice can be sprinkled gently over the cap, slowly wetting it, or it can be shot at high pressure, breaking up the cap and redistributing the solids within it. A "pumpover" can also be a useful way to add the yeast.

    Punch Down Pump Over

    Both "punching down" and "pumping over" achieve the dual goal of both keeping the "cap" wet (preventing it going volatile) and extracting more colour and tannins.

    One additional technique is called "
    rack and return" (délestage in French), which is a two-step process in which fermenting red wine must is separated from the solids by racking and then returning to the fermentation vessel to re-soak the solids. Racking the fermenting juice oxygenates, or aerates, the wine and softens astringent tannins through oxidation. During delestage, the cap falls to the bottom of the vat as the wine is allowed to drain completely. Once the wine is completely racked, some seeds is removed to avoid imparting overly harsh tannins to the wine. Following racking, grape solids are allowed to settle separately from the fermenting wine for a few hours or more depending on the size of the fermenting vat. The fermenting wine is returned to the vat over the cap using a gentle, high-volume pump to completely soak the grape solids for maximum colour and flavour extraction while minimising extraction of harsh phenols.

    Within the "cap" there is a high concentration of
    yeasts, not only from the "pruina" (pruinosity) covering the grape's surface, but also because the layer absorbs yeast cells from the must. These yeasts produce a more intense fermentation and the "cap" temperature increases faster than in the liquid. This higher temperature promotes a better extraction, however the temperature should be kept under 35°C otherwise the yeast can be damaged, and might even stop the fermentation process.
    Open-top fermenters allow for increased oxygen, which is advantageous for yeast health toward the start of a ferment. Open-top fermenters also allow winemakers easy access to the "cap". Furthermore, heat generated during fermentation can more easily escape, thus open-top may help better manage fermentation temperatures. Fermentation tanks are often slightly tapered toward the top, so that "punchdown" may be less "violent" than in a straight-sided tank. The taper yields a "cap" of smaller diameter, meaning the juice is more easily displaced as the cap is submerged.

    The earliest containers were stone troughs,
    amphora, and later "tinaja" or terracotta storage vessels (which have been re-introduced by a few winemakers). Oak barrels and vats have been used in fermentation processes for several centuries. Their main advantage is the transfer and improved integration of aromatic compounds from the oak staves during the fermentation process, and the inside of the vat is usually charred to increase this effect. Oak vats are usually mid-sized and have a similar height and diameter, in order to obtain those thin "caps". Wine grape tannins appear better integrated when fermentation takes place in oak vats, and they appear to produce full-bodied wines with a soft astringency. More over the thermal inertia of oak vats also facilitates a better malolactic fermentation. Perhaps the biggest difficult is in the cleaning and removing undesired bacteria and yeasts. Concrete tanks are becoming again increasingly popular, in part because they are easy to build and less expensive, although they now are usually also treated inside with a food-safe epoxy covering. Originally these tanks were replaced by stainless steel tanks that were more hygienic and where the temperature could be more easily controlled. Concrete tanks are said to have a very good thermal inertia, so making the development of lactic acid bacteria and colloidal precipitations easier. However cone shaped stainless steel tanks are probably the most practical option (i.e. easy to build, clean, sanitise, etc.). They have good thermal transfer properties so refrigeration during fermentation is very effective, but convecting currents inside the tanks can hamper settling and colloidal stabilisation (i.e. suspension of insoluble particles).

    One addition option is to use a
    submerged "cap" (chapeau submergé in French), which is a technique widely used in Europe during the 19th century. Rather than "punching down" or "pumping over", the submerged method holds the "cap" under the surface of the must for a fixed period of time (often until dry) meaning it remains permanently in contact, but not disrupted, with the must. The method has been shown to yield wines which are richer in tannins and colour when compared to the same wine subject to floating "cap". There are a few alternative techniques, which I understand to be prohibited in Rioja wine production, namely, horizontal rotary fermenters, thermovinification involving the heating of whole or crushed grapes to promote rapid extraction of phenolic compounds, and "pulsair" (pneumatage French), where the must is brought up and over the cap through the use of large burst of compressed air through injection probes. The rising bubbles break up the cap into individual berries and the wine juice spills up and over the top.

    There is a considerable diversity in size, shape, design and construction materials used in fermentation vessels in winemaking, and almost any non-porous and non-toxic material can be used in a fermenter. All the vessels can be categorised in two basic categories, i.e. vats and tanks. The only real different is that vats are open-topped, while tanks have sealed tops. Historically, vats were used in red wine production because a direct access to the cap of skins was required during fermentation. White wines can be vinified in tanks and have an advantage that oxygen can be excluded from the fermenting juice. Most fermenters are of a simple design, but they can become more complex the larger the volume. And as the volume increases it reduces the relative surface area for heat transfer. In red wine production, the complexity of the vessel design depends upon the technique used for submersion of the "cap".

    Conventionally, the
    batch system of fermentation is used in wineries, however, continuous fermenters do exist but are rarely used. I think the Rioja rules and regulations prohibits both continuous fermenters, rotary horizontal fermenters and tanks with rotating blades inside, but not the use of amphora, concrete or even plastic fermenters.


    A design sketch showing different components of a stainless steel fermenter is shown inFig. 1. Small fermenters are rarely used in red wine fermentation due to the difficulty in achieving adequate cap submersion.

    Commercial wineries are using fermenters of 200 hL or more capacity.These are cost effective in terms of capital outlay, mechanization and automation.

    Fermenters of a wide variety of shapes like upright-cylindrical (Plate 24.2), horizontal- cylindrical, V-shaped, square tanks, etc. are used in wine production.18 The shapes of different fermenters used in alcoholic beverage fermentation183,188 are shown in Fig. 2. In most of the fermenters, floor sloping is inclined towards the front. Fermenters with hemispherical or domed bases are used in wine making. In spite of advantages in pomace discharge in red wine making, the use of conical-based fermenters has not been practiced. One of the newest and most expensive innovations in red wine fermentation is the rotating stainless steel fermenters (Plate 24.3) which are very efficient with respect to the extent oftime and energy needed to gain optimal skin exposure to the fermenting wine and minimal oxygenexpose to spoilage organisms. In spite of having advantages, the use of rolling and cylindrical vesselsas an alternative to conventional fermenters has found limited acceptance in red wines.212The various types of ‘Defranceschi’ red wine fermenters have the option of automatic discharge,pumping over, plunging system, etc. and are used in wineries throughout the world. In South Africa,Grotto defranceschi now produces wine tanks as well as the ‘FermentamaticR’ with pump-over andautomatic discharge facility (Plate 24.4) and ‘CPR’ (plunging models). Over the last few years, thesefermenters have become well known in the wine industry and are used by a large number of producersof high quality wines. Both the types can be fitted with a central filter column. Various fermenterdesigns with automated control systems have been reviewed.212 An automatic fermentation tank formaking of red wine has been recently patented in USA.9
    2.3.2 Construction materialThe fermentation vessels are primarily made-up of stainless steel, fiberglass, cement, plastics and non-aromatic wood. Generally, stainless steel is preferred to other materials because of its properties like
    Bioreactor Technology in Wine Production 811strength, long lasting, impervious nature, corrosion proof, rapid heat transfer, aromatic neutrality,formation in to any size or shape and easy to clean. This inert material is ideally suited to all forms oftemperature control and has a capacity to produce the freshest wines with purest varietal character. Thefermenters may be constructed with a jacket in which coolant is circulated for temperature control.189Fermenters made-up of materials other than stainless steel, require periodic pumping of the fermentingjuice through external cooling coils or the cooling coils are inserted into the fermenting juice. The onlydisadvantage of the stainless steel vessels is being expensive.Fibre glass is considerably less expensive and has most of the properties of stainless steel. But the heatconducting properties of stainless steel are lacking. To avoid the slow release of styrene and othercompounds in wine, a proper curing of fibreglass is essential during manufacturing. Although, cementis less expensive, but have poor heat conductivity and no mobility. The coating of inner surface ofcement vessels with wax or tiles is essential to prevent calcium uptake during fermentation.The wooden vessels are expensive, have a comparatively limited life, are not easy to clean, can’t besterilized, possess poor heat conductivity making temperature control very difficult and restrictions inshaping and design. These vessels are neither impervious nor inert but allows access to the air whichcauses faster oxidation and evaporation which concentrates the flavour in wine. Wines fermented inbarrels have more quantities of higher alcohols but lower in fatty acid esters, resulting in a less fruitycharacter in wine. Furan aldehydes, many of which have the aroma of grilled almonds are reduced byyeast during barrel fermentation, resulting in formation of furfuryl alcohols.34 Oak imparts woodtannins to low tannin wines, absorbs tannins from very high tannic wine or can simply exchangetannins with some wines. Fermentation in oak barrels leads to production of wines with much morecomplex sensory properties, largely attributed to the phenols extracted from oak wood.123 Vanillin, theessential aromatic of vanilla pods, is also extracted from the oak by oxidation, and together withvarious wood lactones and unfermentable sugars, imparting a distinctive, sweet and creamy nuance tothe wine matured in wood. But an increase in occurrence of hydrogen sulphide has been found in alloak types when associated with fermentation and sur lie aging.52 The occurrence of hydrogen sulphidein minor quantities has been associated with oak chips with regard to the intensity and duration of thesulphide compounds and to be endemic with fermentation on oak chips.Wooden or cement vessels are now replaced by well designed stainless steel fermenters. An Australianfirm has gone one step further by constructing a square stainless-steel tank with two oak panels that arecomprised of oak staves that can be replaced, reversed and even adjusted in size to give different oak towine ratios.
    Plastic containers are inexpensive alternative to the traditional red wine fermentation vessels which areusually made from stainless steel, cement or wood. “A plastic container that collapses as liquid isdispensed” was used in Europe for at least twenty years before its adoption in Australia. HickinbothamJr. has invented a disposable ‘FermentabagTM’. Plate 24.5 illustrates the view of fermentabags beingused for fermentation of wine and an individual bag is also shown in inset. This flexible fermentationcell is made up of highest food grade specialized plastics (multilayered polyurethane) and is of 1000 L
    Handbook of Enology: Principles, Practices and Recent Innovations812capacity with a breather pipe in the middle. This material allows for specific amounts of air to bepassed through the film to the wine and allows for a ‘micro-oxygenation’ effect similar to that of oakbarrel. FermentabagTM is designed for fermentation of red wine only but can also be used for storage ofred wines for 4-6 weeks after fermentation is complete to allow for maceration. The system is alsosuitable for carbonic maceration. It is extremely important that it is filled up to 90-97% full capacity.Warm water or brine can be added via the auxiliary ports to speed up or kick start the fermentation incool climates. It is designed in a way to continuously circulate the wine through the cap duringfermentation and thus, eliminate the need to plunge or “punch down” the cap. These bags are placed inspecified rigid containers and can be moved from one floor to another during fermentation or maceration.There are provisions in the plastic bags to draw samples during fermentation and produce softer tanninedand better coloured wines





    The most important
    phenolic compounds in red wines are pigments and tannins, and anthocyanins are the pigments. Anthocyanins are in fact coloured molecules with a flavonoid structure and visible absorbance maximums ranging between 518 nm and 538 nm in wine grapes. So on average they absorb light of 525 nm and are responsible for the colour of red wine, i.e. absorbance in the region 480 nm to 540 nm corresponds to blue-green, green, and yellow-green, allowing the preferential transmission of violet (380-420 nm) and orange-red (580-800 nm). Tannins are a colloquial name used for proanthocyanidin compounds again with flavonoid structures, and they are responsibly for the structure, astringency and antioxidant capacity of red wines. Furthermore, they have some antimicrobial effect, contributing to the stability of red wine pH and alcohol levels. As anthocyanins and tannins are mainly found in the skins, it's necessary to extract them during maceration and to diffuse them in the must so that the wine acquires a suitable colour and structure. This process occurs during maceration, and at the same time as the alcoholic fermentation. However, the chemical nature of pigments and tannins are completely different. So what happens is that at the beginning of fermentation, the must is essentially acidic water with sugars, and the solubility of anthocyanins is very high, so the extraction happens really fast (i.e. by day 3 or 4). After that time, the ethanol concentration is high enough to reduce anthocyanin solubility, causing a decease in colour intensity. The concentration of anthocyanins will stabilise when all sugars are fermented and the maximum ethanol level is reached. With tannins, the concentration increases with ethanol levels, reaching a maximum at the end of fermentation. Below we can see this, with colour intensity (little squares) and the tannins (little circles).

    Kinetics of Extraction

    There are several ways this process can be influenced. A "cold soak" means lowering maceration temperature (to between 4°C and 15°C), i.e. the refrigeration of the must to delay the beginning of fermentation. This means that the maceration is done in the absence of ethanol, so a selective extraction of anthocyanins as compared to tannins. Winemakers can also simply cool the crushed grapes, or use a cooling jacket on the tanks. Some producers even add dry ice, which also breaks the skins and facilitates the rapid release of phenolic compounds. An alternative is to thermal process (thermovinification) the crushed grapes or skins, by raising the temperature to between 40°C and 70°C for between 15-60 minutes. This also accelerates the extraction of phenolic compounds, and has the added advantage of reducing the effects of wind on yeasts and bacteria. The downside is a loss of aromatic compounds and possible thermal degradation. The negative effects of thermal processing can be reduced using the so-called "flash détente". Firstly the grapes are heated for a short time to 85°C, affecting the skins but not the pulp. Then placed in a vacuum chamber, the depressurisation (50 to 75 Mbar) results in the liquid exploding (boiling) in the skins, facilitating a fast extraction of tannins and pigments. This process is said to enhance extraction of both anthocyanins and tannins, and still allow fermentation to develop at low temperatures. However the rules applied to Rioja wines strictly prohibits "grape preheating or the heating of must or wine when in contact with pomace (i.e. solid remains of the grape) in order to extract colouring matter".
    Mechanical treatment of the "cap" helps promote extraction and diffusion in the
    must during fermentation. "Punching down" and "pump overs" (remontage in French) are ways to do this. "Punching down" is done to increase the extraction of skin phenols, to homogenise skins and liquid, and to diffuse the phenols in the liquid (it also balances the temperature in the tank). It is done using sticks with flat plates (see the effect below). "Punch down" takes a lot of effort to disaggregate the cap and homogenise the content, and it can be done as frequently as needed. There are several mechanical devices that can be used to do a "punch down", e.g. using one or more hydraulic pistons.

    Punch Down

    "Pump overs" do the same, and involves extracting by gravity the liquid from the bottom of the tank and irrigating the cap surface. Sometime a grid is inserted to breakup and aerate the liquid as it is pumped over the cap. A "pump over" will aerate the must, help the yeast to develop at the beginning of the fermentation process, help the extraction and diffusion of phenolic compounds from the skins, and homogenise the tank temperature. Experts suggest that a "pump over" should involved between 40% and 60% of the tank volume, and can be performed between one and three times daily. But much depends on the grape variety, phenolic ropiness, skin hardness and thickness, vine age, pH levels and alcoholic degree.

    In our "example winery", the grapes are first de-stemmed, crushed, and then "
    fermented" in stainless steel tanks for eight days at a controlled temperature and in constant skin contact. During "fermentation", "pumping over" (pumping the liquid over the solids) and "punching down" (pushing the solids into the liquid) are regularly carried out. These processes ensure an improved colour and aroma extraction.
    Some winemakers prefer to avoid destemming and crushing, and just press gently the grapes to start fermentation. Still other winemakers keep a percentage of stems during fermentation to extract more structure, colour, and texture. Some winemakers describe a "semi-carbonic fermentation" process, similar to the method traditionally used in
    Rioja Alavesa, others have described it as a "pre-fermentation cold soak carried out for a period of 6 days at 5°C, followed by a temperature-controlled fermentation at 28°C for 14 days with 3 daily pump-overs" (for a total maceration time of 20 days). Variations are abundant, with a different winemaker using a cold maceration period of four days, followed by alcoholic fermentation at 28°C for ten days, maceration for another ten days, before the completion of a malolactic fermentation. Another winemaker described a process involving the cold maceration of the grapes at 6°C for 12 hours, before pressing and fermentation under strict temperature control to avoid exceeding 15°C. Yet another winemaker wrote of a period of cold maceration (48-72 hours) followed by fermentation in stainless steel tanks at 21°C to 23°C over a period of around 8-10 days. One mentioned the "cold soak" step lasting 3-4 days, with a gentle "pump over" 2-3 times daily. This was followed by a fermentation period of between 10 and 35 days depending upon grape variety and maturity. When the fermentable sugars had dropped by about one-third, a commercial strain yeast was added. The peak fermentation temperature was just below 30°C, and a pump-over was performed twice daily. The "free run" and press fraction were kept separate, and when the initial formation was completed the must was inoculated with lactic acid bacteria, and the malolactic fermentation finished in the barrels after about 6-8 weeks. The wines would be racked once, and a small does of sulphur dioxide added.
    Just to make life more interesting, many winemakers adopt a "semi-carbonic fermentation" process, but just call it "carbonic". In the Beaujolais region some winemakers simply call it "
    maceration traditionnelle", whilst others prefer a yeast fermentation because it's said to express better their unique terroir. Just as some winemakers in the Beaujolais region have turned away from "semi-carbonic fermentation", others around the world are adopting the process to make easy to drink "glou-glou" wines ("glug-glug" in English).
    From the above descriptions, temperature is one critical parameter, since it affects the rate at which berries absorb carbon dioxide. At 35°C about 50% of the volume of carbon dioxide will be absorbed, and "berry death" will take about one week. At 15°C, the fruit will absorb less carbon dioxide, and can take in excess of 20 days to produce a wine (but with significantly less
    aroma).

    Carbonic maceration can completely change a wine's style and flavour profile, and is often associated with making light-to-medium-bodied red wines fruitier and with softer tannins. A carbonic maceration (a termed often preferred to the simple "fermentation") is where whole grapes are fermented in a carbon dioxide rich atmosphere (anaerobiosis) for several days so that enzymatic reactions take place without yeast participation. The normal alternative is to crush the grapes to free the juice and pulp and let yeasts convert the sugar into ethanol. Carbonic maceration ferments most of the juice while it is still inside the grape, although grapes at the bottom of the vessel are crushed by gravity and undergo conventional fermentation. What this means is that the initial fermentation occurs intracellularly, or from inside the grape. In an oxygen-free environment, the berries begin to ferment from the inside, and they use the available carbon dioxide to break down the sugars and malic acid, producing alcohol and a wide range of flavour compounds. It's worth mentioning that the ADH (alcohol dehydrogenase) enzyme is already detectable in grape after veraison, and levels increase gradually during ripening, and small amounts of ethanol are already being produced inside (but insufficient to burst the skin).
    In practice carbonic maceration is a pre-fermentation treatment and involves keeping the intact grapes in a carbon dioxide environment at an elevated temperature (20°C to 35°C) for 8 to 10 days. It is an
    enzymatic process that occurs in whole grapes and is quite distinct from microbial fermentation. In this process, the intact grapes go through a partial fermentation by glycolytic enzymes present in the grapes. This self-fermentation generates unique flavours associated with carbonic maceration. The alcohol produced during intracellular fermentation helps to dissolve the skin and it becomes eroded resulting in the expulsion of alcoholic grape juice from the grape. Carbonic maceration does not involve any physical movement of the grapes to extract extra colour or tannins from the skins. The weight of the grapes lying on top of one another, is enough to cause the grapes to be crushed and release their natural juice known as the "free run" juice. Carbon dioxide generated by the fermentation of crushed grapes is held under a modest pressure in the tank until the desired colour and flavour extraction is achieved. Several unique changes that occur in berry composition during carbonic maceration are due to the activation of shikimic acid pathway. The juice elaborated by maceration contains ethanol (1.5 to 2.5 g/l), nitrogenous compounds, inorganic matter, polyphenols and aromatic compounds. Immediately this is followed by the pressing of the remains after the "free run" juice has been collected. Following carbonic maceration if the "free run" juice shows the symptoms of undergoing a simultaneous alcoholic fermentation and malolactic fermentation, then it is usually kept separately from the "press run" juice. Otherwise, both of the fractions can be fermented together. The different treatments are followed because the sugars in the "press run" juice may promote excessive acetic acid synthesis by the lactic acid bacteria conducting malolactic fermentation. Both juice fractions can be fermented separately and thereafter, may be blended selectively.


    Carbonic and Normal Grapes

    Above the grape on the left has a darker flesh because it has undergone carbonic maceration, whereas on the right we have a normal grape. The flesh becomes darker because polyphenols (tannins and anthocyanins) make their way into the pulp form the skin. Once the alcohol content reaches about 2%, the berry bursts, and the result is fruity wine but with very low tannins. This type of wine lacks the structure for long-term ageing, and should be drunk young (i.e. this process is typical to the Beaujolais region, and in particular for Beaujolais Nouveau).

    "
    Semi-carbonic maceration" involves a short period of carbonic maceration (2-7 days), followed by conventional yeast fermentation. An alternative name for carbonic maceration is "whole grape fermentation", which is distinct from the process of "whole bunch fermentation" (i.e. including stems).

    To some extent, most wines were historically treated to some form of semi or partial carbonic fermentation, and the deeper the vessel, the greater the proportion of grapes that could be exposed to an
    anaerobic environment caused by the release of carbon dioxide from the crushed grapes on the bottom. In fact, carbonic maceration was the only method used in Rioja until the introduction in the late 18th century of destemming (or Bordeaux method), the method most extensively used worldwide to make wine by first removing the stems and then crushing the grapes. In the Rioja Alavesa the carbonic maceration process is used, but not strictly adhered to. Usually whole bunches are placed in open vats or "lagar", sulphur dioxide is added, carbon dioxide is not added, and it is not fundamental that all the grapes be intact. The berries at the bottom are crushed by the weight, thus also initialising the fermentation by yeast, so both phenomena take place simultaneously.

    It was
    Michel Flanzy who is credited with re-discovering carbonic maceration in 1934, whilst looking at the use of carbon dioxide as a grape preservation technique. And it was in the 1960's that Jules Chauvet re-introduced the technique, in particular in the movement towards natural wines, i.e. wines made with traditional methods.

    One description of the traditional
    Bordeaux method in winemaking began with selecting the grape varieties best suited to the local conditions of soil and climate. The principal Bordeaux red wine varieties are Cabernet Sauvignon, Merlot and Cabernet Franc, originally grown by a specific form of "layering" (marcottage) called "provignage" (a form of ground layering), and now by grafting. The vines were pruned of dead wood in February (triage des bois), and suckering and disbudding (removal of shoots and buds) was performed in May. The grapes were harvested at maturity, which sometimes involved several passages in the vines or even spreading the harvest depending on the exposure of the plots. The grapes were then transported with precaution and without delay to the presses, in order to limit premature oxidation. During winemaking, the stalks were separated from the berries before pressing. Fermentation was carried out in one go, whereas in Rioja the grapes were added to vats where previously harvested grapes were already fermented, which seriously affected the homogeneity of the fermentation. In Bordeaux topping up was made in the vats, to avoid contact with air as much as possible. Once the wine had been placed in oak barrels, regular racking was carried out to remove the lees and impurities from the wine, and frequent topping to prevent oxidation. The wine was then clarified, often using egg white, and the duration of ageing in barrels was programmed according to the characteristics of the wine. Today in Bordeaux, after destemming and light crushing, the alcoholic fermentation is followed by a natural malolactic fermentation lasting up to three months, the lees being stirred once a week. Traditionally Bordeaux wine was aged for 16 months in either new American oak or in twice-used French oak, and the wine was racked three times.

    In traditional
    maceration, the crushed grapes are transferred to the fermentation tanks and inoculated with a yeast culture. Generally, stainless steel tanks or large oak containers are used for fermentation. The maceration and fermentation occurs simultaneously in this conventional method. Some wineries use only the naturally occurring yeasts that are found on the grapes. Yeasts of the genera Hanseniaspora and Candida are the predominant species on the surface of the grapes, accounting for about 50% to 75% of the total yeast population. They dominate the early stages of spontaneous fermentation, followed by variety of species such as Cryptococcus, etc., in the middle stages when the ethanol level rises to 3-4%. The last stages of fermentation are invariably dominated by the alcohol tolerant strains of Saccharomyces. S. cerevisiae is universally known as the wine yeast and is ultimately responsible for the alcoholic fermentation. However, other non-Saccharomyces yeasts, such as species of Brettanomyces and Zygosaccharomyces, also may be present during the fermentation and can even appear in the wine. Tailor made wine yeast strains are increasingly used to improve the reliability of fermentation, wine quality and economics of production. The length of the maceration and fermentation depends entirely on the level of tannins and the colour desired in the final wine. Short fermentation periods produce lighter wines, while longer fermentation times are used to obtain wines with a more intense colour. Generally, the total fermentation of grape sugars is carried out for 5-8 days. It is done at a relatively high temperature of 25°C to 30°C, since it enhances colour extraction. When the active fermentation starts, the solids (skins) will rise to the top of the juice and form a skin "cap" that can occupy up to one-third of the fermenting volume. A number of methods can be employed to continue to bring the skins in contact with the must, such as the use of submerged caps, pumps, agitators, etc.

    After the initial
    maceration and alcoholic fermentation, the juice is transferred a second stage of vinification, the so-called malolactic fermentation. We can also see that the skins are pressed in a vertical press, and the juice drained by gravity is mixed with the juice from the initial fermentation.

    Most
    wineries use "rack and return" (délestage in French) to improve phenolic extraction. The easiest way is to "rack" the juice into another tank, leaving only the skins in the bottom of the original fermentation tank. Normally the skin "cap" is floating on the must-wine surface, and when the juice is removed the cap gradually descends to the bottom of the tank. After a few hours the juice is then added again on top of the cap. The cap is disaggregated, facilitating the diffusion of pigments and tannins into the juice. Later the cap will reform, but the tank contents have been aerated and homogenised, and the temperature has also been equilibrated. Some wineries pour the returning juice, other are known to place the full tank over the emptied tank and release the juice in a few seconds, producing an intense release of pigments and tannins from the cap. Yet other wineries are known to inflate a big balloon inside the tank, gently increasing the pressure on the skins. Some wineries also use racking to remove the grape seeds, which would otherwise add harsh tannins. The overall idea of this process is to extract phenolic compounds in a smooth manner, increasing the body and structure of the wine, and reducing astringency, bitterness, and dryness. "Rack and return" demands more equipment and properly trained staff, so it is not always practices by all the wineries, however, even just one "rack and return" can increase the total polyphenol index considerably.

    Effect of Rack and return

    Generally "rack and return" is performed only once the cap has formed properly, but not too later, because the fermentation rate will be low and the cap might not reform (see above). The cap surface is usually exposed to air, so is sensitive to oxidation. One technique is to place a metallic grid inside a specially designed tank to keep the cap just under the surface of the juice.

    The
    maceration time can be extended after the end of fermentation from a few days to, in some cases, more than one month. The advantage to delaying the removal of the pomace is that maceration will continue in the presence of a high ethanol concentration, thus improving tannin solubility. As the skin cell walls degrade the extraction process is enhanced, and higher levels of anthocyanins are obtained.

    One objective is to separate the maceration and fermentation processes, i.e. first extract the
    anthocyanins and tannins, then ferment at a lower temperature, thus reducing the role of wild yeasts and bacteria, and promoting the role of the inoculated yeast starter. One "high-tech" option is to try to apply a "high hydrostatic pressure" to the grape in all directions. Avoiding the application of pressure in just one direction keeps the grape wall intact, and a high enough pressure kills the wild yeast population. This technique when applied for a few minutes improves phenol extraction and colour. It also allows the use of a yeast-bacteria co-inoculation to perform simultaneously alcoholic and malolactic fermentation, and allows sulphur dioxide levels to be kept low. If the pressure is applied along with oak chips, it accelerates the ageing of young wines. So-called "pulse electric fields" is another non-thermal "high-tech" option that increases substantially the extraction of phenolic compounds and reduces the maceration time. Ultrasound can also be used to destroy the cell walls of the skins and improve dramatically the extraction of phenolic compounds, thus also reducing the maceration time.

    However the rules applied to
    Rioja wines strictly prohibits both "unsuitable pressure levels" and "grape preheating or the heating of must or wine when in contact with pomace (i.e. solid remains of the grape) in order to extract colouring matter". Also the use of pieces of oak wood (chips, etc.) during production or ageing is prohibited. So most of the "modern day" or "high-tech" options are not allowed.



    Crushing the whole clusters of fresh
    ripe grapes is traditionally the next step in the wine making process. Today, mechanical crushers replace the time-honoured tradition of treading the grapes into what is commonly referred to as must. For thousands of years, it was men and women who performed the harvest and "danced" in vats as the first step towards making wine. Mechanical presses have removed much of the romance and ritual in winemaking, but they have improved the quality and longevity of wine, while reducing the winemaker's need for preservatives. Having said all this, it is important to note that not all wine begins life in a crusher. Sometimes, winemakers choose to allow fermentation to begin inside uncrushed whole grape clusters, allowing the natural weight of the grapes and the onset of fermentation to burst the skins of the grapes before pressing the uncrushed clusters.
    Up until crushing and pressing the steps for making white wine and red wine are essentially the same. However, if a winemaker is to make white wine, he or she will quickly press the must after crushing in order to separate the juice from the skins,
    seeds, and solids. By doing so unwanted colour (which comes from the skin of the grape, not the juice) and tannins cannot leach into the white wine. Essentially, white wine is allowed very little skin contact, while red wine is left in contact with its skins to garner colour, flavour, and additional tannins during the next step, i.e. fermentation.

    If there is a major phase in
    winemaking, then it must be fermentation. If left to its own devices must or juice will begin fermenting naturally within 6-12 hours with the aid of wild yeasts in the air. In properly managed vineyards and very clean wineries this natural fermentation is a welcome phenomenon. However, for a variety of reasons, many winemakers prefer to intervene at this stage by inoculating the natural must. This means they will kill the wild and sometimes unpredictable natural yeasts and then introduce a strain of yeast of personal choosing in order to more easily predict the end result. Regardless of the chosen path, once