The chemical analysis of wines...
The sugar level
This indicator is essential during the vinification, it allows us to anticipate the moment of harvest as soon as we start to control the maturity. To produce 1% alcohol by volume, it is generally necessary to raise almost 17g/l of sugar according to the selected yeast strains.
The monitoring of the alcoholic fermentation is carried out by measuring the levels of sugar transformed into alcohol under the effect of the yeasts. It may be that the fermentation does not degrade all the sugars, in which case we speak of residual sugars. These sugars may contribute to the balance of the wine.
The alcohol level
The TAVP (potential alcoholic strength by volume) is calculated by the following formula: TS/16.83. This represents the alcohol content that is generated by the yeasts during fermentation.
We also find in the alcohol level the TAC: acquired alcoholic strength. The TAC is used to determine the rate that is actually in the wine during fermentation or when the wine is ready to be bottled.
The different alcohol levels will define what is called the "gustatory approach" of a wine. The alcohol content does not define the quality of a wine, but the notion of the balance of the different components such as sugar, acidity. The quality of the winemaking process and the quality of the grapes help to develop the structure and balance of a wine.
It is important to understand that wine is not only the combination of grape and sugar but also the know-how comes into play with the acidity.
Mineral and organic acids are part of the wine, some are part of the perception of taste, others are not. The combination of all these free and partly free acids forms the acidity of the wine.
There are 3 families of acids:
▪ Tartaric acid, is only found in wine and grapes (none in nature).
▪ Malic acid, found in fruits and vegetables.
▪ Citric acid, especially during noble rot or by enriching the grape with sugar by concentration.
The pH is used to measure the notion of acidity (identical to the readings, for example, in a swimming pool). It is completely dependent on tartaric acid for wine.
Volatile acidity can have several origins:
▪ It can be of physico-chemical origin during ageing in wood due to the extraction of acetic acid from the wood.
▪ Or of microbiological origin during the transformation of citric acid and residual sugars into acetic acid by lactic acid bacteria during malolactic fermentation.
▪ Or from the formation of acetic acid by yeasts during alcoholic fermentation.
▪ Or from the oxidation-reduction of carbohydrates and ethanol into acetic acid by acetic bacteria (acetobacter aceti).
In France, the rules of the AOC (Appellation d'Origine Contrôlée) regulate this acidity which must not exceed 0.9g/l. For your information, this is expressed as H2SO4 (for 1.35g/l in tartaric and 1.1g/l in acetic). However, the feeling will depend on the balance of the wine.
Malic and lactic acid
As seen above, these two natural acids come from grapes.
Malic acid is a green acid that is less digestible than lactic acid. This is why the wine will naturally go through malolactic fermentation at the same time as it ferments or later in the year, in the spring, when the cellars warm up. This malolactic fermentation is a natural deacidification of the wine. It is therefore the malic acid that will be transformed into lactic acid under the action of lactic bacteria (oenococcus oeni). Simple, no!
This acid is a formative factor in the great wines in the making. It helps them to preserve the authenticity of their freshness over time. As I said above, it is almost only present in grapes but also in green tea.