The starting point for the entire process is the grapes themselves, whose chemical and physical composition can be measured when they reach the winery and after they have been transformed into must. This “raw material” is then transformed by the metabolic activity of yeasts and bacteria during the alcoholic fermentation, creating the fundamental alteration of must into wine, with the formation of ethyl alcohol, carbon dioxide, heat and other secondary compounds. The options of malolactic fermentation and storage in wooden barrels – as well as a whole host of other winery operations – will also create further compounds that characterize the wine in various ways.

Among the main components of a wine we undoubtedly find:

•   ethyl alcohol
•   sugars
•   and acids.

Ethyl alcohol

If we exclude water, which on average makes up between 80% and 85%, and dessert wines with residual sugar of over 130-140 g/liter, the major component in wine is ethyl alcohol, which represents on average between 11% and 14%.

The wine’s potential quantity of ethyl alcohol has always been considered (though nowadays a little less) as a quality factor, to the extent that it represents the basis for calculating the price of bulk wine: this is partly because it expresses the sugar level of the grapes, which naturally depends on their degree of ripeness (but also on the variety, the cultivation zone, etc.).

In order to calculate the total level of alcohol one has to multiply the percentage of (fermentable) sugars in the must by a coefficient of 0.6. Essentially, a must with 200 g/l of sugar (i.e. 20% of its total weight) should, when fermentation is completed, give a wine with around 12% vol. (20 x 0.6). The % vol. indicates the quantity of alcohol in milliliters (cubic centimeters) contained in 100 milliliters of wine.

The total alcohol level results from the sum of the actual alcohol and that which can potentially be developed by the transformation of fermentable sugars that are still present (medium-sweet or sweet wines).

Sensory effects

If it is present to a high degree, ethyl alcohol provokes a pungent sensation on the nose. It gives a generally sweet, rounded flavor on the palate and, especially if it is high, a sensation of apparent warmth.

Sugars

These are the dominant element in the must following the crushing of the grapes: they are normally present in quantities that vary between 160 and 220 g/liter, sometimes reaching over 300 g/liter in musts obtained from dried grapes. Following the alcoholic fermentation and the metabolic activity of the yeasts, the sugars vanish almost completely in dry wines, remaining in quantities of below 4 g/liter, whereas more appreciable amounts are to be found in medium (“abboccato”) wines (up to 12 g/l), still more in medium-sweet (“amabile”) ones (from 12 to 45 g/l), and a high level is present in sweet wines (residual sugar > 45 g/l).

Sensory effects

The presence of sugars causes a particular sensation of sweetness, balancing out both bitterness and acidity, and increasing the roundedness and softness one perceives in the wine. In the case of truly sweet wines, these sensations have to be balanced by marked acidity in order for the wine not to appear cloying.

Acidity

The acidity of a wine is a very significant factor in terms of its sensory characteristics (freshness of taste, brightness of color) and of its keeping potential.

A wine’s acidity can be measured in real terms by its pH (hydrogen ions liberated in solution) or in titratable terms, when it is expressed in g/l of equivalent tartaric acid (presence of various organic acids, which are potentially separable, in a hydro-alcoholic solution).

Total acidity can be divided up between fixed acidity (acids that do not evaporate if the wine is distilled) and volatile acidity (acids that volatilize when the wine is boiled). When one talks in general terms about the acidity of a wine one means just its fixed acidity, unless one specifies its volatile acidity as well.

Among the fixed acids are tartaric, malic, citric (all present in the must) as well as succinic and lactic acids (deriving from the alcoholic and malolactic fermentations), while the volatile acids include acetic, butyric and propionic acids (these last two are present only in very tiny quantities).

Volatile acidity

The volatile acidity of a wine is linked to the presence of acetic acid (and to a much lesser extent to formic, butyric and propionic acids).

It is a natural product of the alcoholic fermentation, which if carried out in a good, regular manner should, however, create low levels of volatile acidity (< 300-400 mg/l).

Sensory effects

When it is present in significant quantities (usually > 600 mg/l, but it depends on the structure of the wine), and especially in the presence of ethyl acetate, produces a sharp odor (varnish), a sour, acescent, bitterish and biting taste, which gives a burning sensation when you swallow the wine.