What is Volatile acidity, how it affects wine and how to measure it?

There are different types of acids in wine, however, based on their characteristics, two separate parameters have been selected for these acids, the measurement of which allows us to more or less judge the characteristics of the wine. These parameters are titratable acidity and volatile acids. Titric acidity includes all types of acids contained in wine, including fatty acids. The name titratable acidity comes from the method of its laboratory measurement, namely the determination of this type of acidity is done by titration with NaoH base. Fatty acids are of different types and include all acids that have volatile properties. To clarify further, certain types of substances are not characterized by the ability to evaporate. In chemistry, evaporation is defined as the property of a substance to describe how well a substance can be converted to a gaseous state. At a given temperature and pressure, a substance with high volatility properties is mostly found in gaseous form, while a substance with low volatility properties appears in liquid or solid form. The most important fatty acid in wine is acetic acid, which in turn is associated with the taste and smell of vinegar, which is produced in wine when the concentration of this acid increases and exceeds the level of perception. Acceptance levels of acetic acid vary from person to person. Perception levels also vary in different types of wine. It is generally believed that the level of acetic acid absorption in wine starts at a concentration of 0.7 g / l. However, very few people can actually perceive this concentration. Perception is also reduced by the various substances contained in wine, including tannins and phenols, and therefore the permissible limits vary according to the categories and style of the wine. For example, for red wine in the US, the maximum permissible acidity is 1.2 g / l, while for white wine it is 1 g / l. It should also be noted that in the case of amber wine, given that such a wine is made on Durdo and in some cases with a long delay on clert with Durdo, most wines have higher tannins than red wines where the delay on Durdo lasts an average of 7-10 days. Therefore, the level of perception in amber wines is also higher than in white wines, and we can assume that it is equal to or may even exceed the amount considered acceptable for red wine. As for non-acrylic acids, most of these acids are found in tartaric acids, although significant amounts of malic acid, lactic acid, or even citric acid may be present, or all together. The production of volatile acidity in wine and the increase in its amount can be caused either by microbiological or chemical processes. A certain amount of volatile acidity is formed in the wine at the initial stage, during its initial fermentation process, therefore there is no wine that will not have volatile acidity at all. At the end of the initial fermentation, if the fermentation has proceeded well, the level of volatile acidity is in the range of approximately 0.3-0.4 mg / L. After that, the level of malic-lactic acid fermentation also increases to some extent. It should be noted that there are differences of opinion regarding the optimal level of acidity. While some winemakers and wine lovers believe that the acidity should be as low as possible and is generally considered so, some consumers note that the relatively high (close to the permissible) level of the wine gives it some complexity and for them it is more interesting and enjoyable. However, it should be borne in mind that the increase in volatile acidity is possible even during aging, even after bottling, and therefore the level close to the limit in turn is associated with very high risks. In all cases, the wine becomes unfit for consumption when the level of volatile acidity in it exceeds the allowable level.

Determination of volatile acidity in wine can be determined by several methods. I will focus on one of these methods that I personally use to analyze my wines. This method is quite simple and although unlike other analyzes such as for the determination of titratable acidity or even the determination of alcohol, this method requires more time, in general even for small cellars in general the procedures are easy to do. First of all, it should be noted that analyzes are not required on a daily basis, but it is recommended to be done at the end of the fermentation to determine the subsequent level of primary fermentation. Then after finishing the secondary fermentation to find out how well the process went. Further analysis can already be done before casting. The analysis is carried out by the method of steam distillation of the wine sample, and then the amount of acetic acid in it is determined by distilling the distillate. For steam distillation analysis we will need 2 flasks, tripod, heat sources (2 pieces), refrigerator for steam cooling, thermometer, tubes for connecting flasks, condensate collecting vessel, 0.1N NaoH, phenolphthalenep 1% water, phenolphthalenep 1% . Preferably, but not necessarily a magnetic stirrer. The picture below shows my assembled system, which cost me about 300 GEL in total. The principle of steam distillation is as follows: Only distilled water is poured into the first flask, this flask acts as a steam generator. This flask is connected to another flask by pouring a mixture of wine sample and distilled water (20 ml. Sample, 75 ml. Distilled water). The steam pipe coming out of the first flask should be inserted into the second flask so that a sample of wine covers this pipe so that the steam "evaporates" during the distillation process. The steam from the second flask flows through the second tube into the refrigerator, where this steam condenses. The solution distilled by this method should be collected in an amount of about 150-200 ml. Then we should add 2-3 drops of phenolphthalein solution to this solution and start titrating with normalized NaoH solution. Fluctuating acidity is calculated using the following formula: VA (g / l) = (ml titrant) (0.1 N NaOH) (0.060) (1000) / (wine sample volume in ml). For example, if we had 20 ml as a wine sample. The wine was taken and the titration took 5 ml. 0.1N normalized NaOH solution, then by inserting the results obtained in the formula we get that the wine had a volatile acidity: VA= 5 * 0.1 * 0.06 * 1000/20 = 1.5 g / l.

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