Analysis

Analysis of alcohol

Wine is a moderately alcoholic drink. Alcohol in wine comes from a natural process called fermentation and is made at the expense of the sugar contained in the grape. Each 17.5 g of sugar giving one degree of alcohol, which is one per cent by volume.

The type of alcohol present in wine is ethanol or ethylic alcohol.

Rioja wines have from 10° to 14° of alcohol. Red wines are usually between 12° and 13°. White and rosé between 10° and 12°. The matter is not simple for whites and rosés. Some years ago, the Market demanded these wines have an alcohol level of 13° and that they be aged in oak. Today, this type of wine is appreciated only by a limited number of consumers. The Market demands whites and rosés with a lower alcohol level. Nevertheless, it is now possible to see a tendency back to the ageing of white wines in wood.

The consumer does not ask for a specific alcohol level, but for wines with "body" and long life (attained with grapes which give almost 13° of alcohol); or light, fresh whites and rosés; these characteristics given by grapes with 11° of alcohol.

For the wine market, the alcohol content is the means by which the cost of the wine is assessed. Nevertheless, Rioja wine is much more than just alcohol, although they are subject to these controls.

For the new red wine 12° of alcohol can be sufficient, while a Gran Reserva red should have from 12.5° to 13.5°. A wine with 14° would have a coarse taste.

Consequently, the analysis of alcohol in wine is very important. There are several abmethods and it is not easy to determine the alcohol content of a wine simply by tasting it. aibsGenerally speaking, methods are established by considering the differences between alcohol and water.

Water has a density of 1.0 and alcohol 0.793. The more alcohol present in wine, the lower its density will be, but acids, sugars and colouring matter are also present and must be separated. To do this, wine is distilled, and the acids, sugars and colouring matter are left as residues, leaving only alcohol and water. A density gauge, calibrated in degrees of alcohol is placed in this distillate and indicates the level of alcohol. This type of density gauge is called a spirit hydrometer and is a reliable and accurate device. It gives measurements to the nearest tenth of a degree.

Water has a density of 1.0; distilled wine with 12° has a density of 0.984 and one of 13°, 0.9828. These figures can only be determined by distillation.

Another method is based on the temperature at which water and alcohol boil. It is called the ebuillometric method and, although not as precise as the previous method, is of practical value. Water boils at 100°C and alcohol in wine at 76°C. The more alcohol present in wine, the lower the temperature will be at which it will boil. However, there is a slight complication; water does not always boil at 100°C. It depends on altitude and climate; at a higher temperature with high atmospheric pressure and at a lower temperature with low atmospheric pressure. The main variant is altitude; at sea level it will boil, theoretically, at 100°C. In Haro (450 m) at about 98°C. Therefore, every time this method is used, it is necessary to check the temperature at which water boils. This method does not require distillation, but cannot be used for sweet wines.

The alcohol level in wines is expressed with the symbol "°", which means degrees and separates units of tenths. It is also expressed with "G.L." , an abbreviation of the name of the French physicist Gay Lussac.

According to EEC regulations, the expression used frequently is "acquired alcohol" which is the number of degrees of alcohol which a sweet wine contains at a given moment. But there is also the expression "total alcohol" which means the degrees that sweet wine would have should its sugar also be transformed into alcohol. With regard to Rioja wines, which, with few exceptions, are not sweet, the expressions "acquired alcohol" and "total alcohol" have the same meaning.

Analysis of acidity

Grapes are an acid fruit and, consequently, wine is an acid drink.

Grapes form numerous acid substances, which are common in the world of fruit. The main acids present in grapes are as follows:

• Tartaric: the prototype of acid in grapes. Can exist up to 7 g/kg in ripe fruit.
• Malic: this is the typical acid of the apple. Green grapes contain a large amount but, when ripe, have very little.

When grapes ferment, these acids are transferred to the wine; in addition, other beneficial acids are formed, as well as some undesirable ones:

• Lactic: this is the acid taste in yogurt and is beneficial.
• Succinic: this is also beneficial.
• Acetic: this is the acid contained in vinegar and is undesirable. Good wine processing should produce a minimum of acetic acid.

The acidity in wine is not usually expressed in terms of the content of each acid, but as the sum of all acids and with reference to the most important of these, which is tartaric.Thus, the total acid content of a wine is calculated and expressed as tartaric acid. This concept is total acidity, which, in Rioja, is usually:

• White..................5.8 gr./l.
• Rosé................5.8 gr./l.
• Young.....................3.5 gr./l.
• Matured red.....................5.7 gr./l.

This determination however does not only indicate only good acids but also includes undesirable ones such as acetic acid. As this acid can be evaporated, it is called a volatile acid. Therefore, volatile acid is undesirable and should be kept to a minimum.

The rest of the acidity, which is called fixed acidity, is favorable.

We have three concepts of acidity. Total acidity which is the sum of fixed acidity and volatile acidity.

Volatile acidity ranges between 0.2 g/l and 1 g per litre in Rioja wines. It is not noticeable on the palate until it has a presence of more than 1 g per litre. The normal values are:

	New	After 1 year	After 3 year	After 10 year
White	0,2	0,3	0,35	--
Rosé	0,2	0,3	0,35	--
Young red	0,15	0,5	0,7	--
Matured	0,3	0,4	0,45	0,6

(gr./l)

These are normal levels in wines of 11° to 13° of alcohol. In the case of higher alcohol levels, volatile acids are higher.

Generally wines have always been evaluated according to a positive factor, the alcohol content; and a negative factor, volatile acidity. This does not occur in areas which produce quality wines, where numerous other factors intervene.

The reader might wonder if acetic acid is an undesirable component and is volatile, why wine is not racked in order to release it. The answer is simply that acetic acid is volatile, but less so than alcohol. If we air it intensely, we would lose more alcohol than acetic acid.

The levels shown are normal in wine-making and conservation, but a wine in cask or bottle can be kept inadequately due to excessive temperatures, thereby increasing its volatile acidity.

There is no efficient or legal method for removing acetic acid from wine. Therefore it is necessary to be extremely careful to make sure it does not increase, either in processing or ageing.

The levels of fixed acidity are the difference between total and volatile acidity.

Volatile acidity is expressed in grammes of acetic acid per litre and total acidity in tartaric as well as fixed acidity. For this reason, in order to subtract these levels, it is necessary to determine beforehand the equivalent of acetic acid in tartaric in order to make a homogeneous subtraction. If a red Rioja wine has a total acidity of 5.4 and a volatile acidity of 0.4, to calculate the fixed acidity it is necessary to take into consideration that 0.4 in acetic acid is equivalent to 0.5 in tartaric, and, as these are homogeneous, the difference, fixed acidity, is 4.9.

According to their fixed acidity, Rioja wines may be used for different purposes. We refer to reds; whites and rosés are always more acid.

In young wines, if their fixed acidity is lower than 4.5 g/l, they will be used as young wines of the vintage. If they have between 4.5. and 5.5, they can be aged and between 5.5 and 7, they can be submitted to ageing over a long period. All this in case of wines with a alcohol level not lower than 12°.

Malic acid in grapes gives wine a disagreeable astringent taste, this is tolerable, to a certain extent, in whites and rosŽs, but not so in reds. For this reason, the techniques used, take advantage of a natural process caused by microbes, called malolactic deacidification. This transforms the malic acid contained in wine into lactic acid, making the wine much more pleasant on the palate. This is fermentation by bacteria which takes place after the main, or vigorous fermentation. It is considered as being a secondary fermentation. For malic acid, a very simple analytical method is used for determining when it has disappeared, and has been be converted into lactic acid.

Analysis of dry extract

In the analysis of wines there is an interesting concept known as dry extract which expresses the amount of dissolved matter which does not evaporate. This extract consists of components such as:

• Fixed acids..............................3-10 gr./l.
• Gliceryne...................................4-7 gr./l.
• Residual sugar.........................1-2 gr./l.
• Natural sugar............................0,5-2 gr./l.
• Minerals in grapes...................1-2 gr./l.

This comes to a total of 20 g/l in white wines, 22 g/l in rosés and 25 g/l in reds. It is a very important concept; wines which have low amounts of these substances are insipid and have little taste, and when in excess, are of average quality.

It is very simple to determine the amount of dry extract and two methods are available. One method, which is simple and accurate, consists of evaporating an amount of wine and weighing the residues left after the wine has evaporated completely at 100°C.

The other system is indirect and is based on the fact that, of the three basic groups of components of wine (water, alcohol and dry extract), water has a fixed density of 1, alcohol has a fixed density of 0.793 and the extract, being dissolved, raises the density of the wine proportionally. Therefore, by knowing the density of a wine and its alcohol level, we know the density which it would have if it only consisted of water and alcohol; the value of the extract is known by means of the density of the wine. These calculations are made with a table and are very simple. The density of wines is easily determined by means of aerometry, when the wine is placed in a test tube. A density gauge, an aerometer is inserted with a stem graduated in density from0.98 to 1.0.

Logically, these measurements have to be made at an extremely accurate temperature as volumes, therefore densities, vary with expansion or contraction. An important component of the extract is the glycerine present in wine. Grapes do not have glycerine; this is formed naturally during fermentation. It is normal for3 to 5 g/l to be formed, but in good red wines of La Rioja, the amount which is formed can reach 7 g/l.

The density of Rioja wines is nearly 0.994, which means that the wine contained in a cask of 225 litres does not exceed 224 kg.

The more alcohol a wine has the lower its density will be.

The values for dry extract vary widely and may be as follows:

Extract	In white wine	In rosé wine	In red wine
16 gr./l.	Very light wine	--	--
18 gr./l.	Very light	Very light wine	Very weak
20 gr./l.	Normal	Very light	Without "body"
22 gr./l.	Acceptable	Little "body"	Light
24 gr./l.	"Heavy"	Normal "Heavy"	Acceptable in old wine
26 gr./l.	--	--	Normal
28 gr./l.	--	--	Normal in young wine
30 gr./l.	--	--	Normal in very young wine
32 gr./l.	--	--	Coarse wine
34 gr./l.	--	--	Sweet or "pressed", not acceptable

This data is only applicable to the typical wines of the Rioja, and not to sweet wines.

Analysis of colour

The substances which produce the natural colouring of wines can be analysed alone, separately or altogether, with a perception similar to that analised by sight.

For overall analysis, a spectrophotometric apparatus is used. Formerly, this consisted of simple colour gauges. The principle of their operation is simple: they measure the amount of light which passes through the wine. The more colour a wine has, the less the proportion of light which will pass through. Hence this involves a light source which sends light to a photometer. An exact amount of wine is placed between them, generally with a thickness of one centimeter.

Daylight is not normally used; one needs light which can be controlled with more accuracy. Therefore, this must be monochromatic and opposite to the colour which one wishes to control.

White wines only have a yellow colour, but reds and rosés have red and yellow. In order to control the yellow colour an opposite colour, blue, is used, and to control red, a green light source. Technically, these lights are defined by their wavelength, i.e., blue has a wavelength of 420 and green, 520.

Whites are measured only with light with a wavelength of 420 and reds with 420 and 520. The more light absorbed the greater the wineÕs colour. This is expressed as a figure which is the sum of the light absorbed by a wine. In general terms this can be expressed for a wine with a thickness of 1 cm in a quartz tank as follows:

Product	Colour
Water	0,00
Very pale white wine	0,03
Pale white wine	0,05
Straw-coloured white wine	0,07
Golden white wine	0,1
Very golden white wine	0,15
Rosé wine with little colour	0,2
Normal rosé wine	0,3
Highly-coloured rosé wine	0,5
Strongly-coloured rosé wine	1
Red wine with very little colour	1,5
Red wine with little colour	2
Very old red wine	3
"Lágrima" red wine of wine-producers	3,2
Reserva red wine	3,3
"Medio" one year red wine of wine-producers	3,5
Matured red wine	3,7
Destemmed red wine of the year	4

This data expresses the amount of colour. However in rosés and reds it is also necessary to represent the quality of the colour, i.e., its tone. This is achieved by considering data on the absorbance of light at 420 and 520, separately and without adding them up. When wine is young, red predominates over yellow. The 420/520 ratio is less than 1. If wine is very old, yellow predominates over red and the ratio exceeds 1.

In the jargon used in laboratories, we talk of colour at 420 and at 520, meaning yellow (controlled by blue light) and red (controlled by green light).