If ethyl alcohol, organic acids (fixed, volatile and pH) and (perhaps) residual sugars are the primary elements to be considered in the chemical analysis of a wine, there are many other substances that, though present in lesser quantities, play a fundamental role in determining the gustatory/tactile characteristics of a wine, thus profoundly influencing its particular taste profile.

An analysis that comprises in a quantitative manner many of these substances (excluding water, alcohols, volatile acids and aromas) is to be obtained from the dry extract.

Dry extract

This is determined by the totality of the non-volatile components of the wine (fixed acids, polyphenols, glycerin, salts, pectins, sugars) and is measured in g/l of fixed residue, taking into consideration, therefore, what is left over after subjecting the wine’s volatile components to evaporation.

As the dry extract is also characterized by the presence of sugars, so as not to have wayward readings when dealing with medium-sweet or sweet wines it is better to talk about the net dry extract (total dry extract minus the sugars).

Substantial values of net dry extract are from 17-20 g/l upwards for white wines and 25-27 g/l for red wines, which have higher values than whites because of the presence of phenolic substances.

Sensory effects

The dry extract is an important parameter that can give a general idea about the depth, concentration, robustness and body of a wine. The higher it is, the more these characteristics should be apparent.

Glycerin

This is an alcohol that forms naturally during the alcoholic fermentation but which we also find to a marked degree in dried grapes.

Its concentration increases in particular according to:

1. the ripeness of the grapes and, consequently, the alcohol level;
2. the drying/shriveling of the grapes, especially if they are affected by noble rot;
3. relatively high fermentation temperatures.

Its range of concentration goes from 2-3 g/l in dry white wines to 7/8 g/l in dry reds and 13-15 g/l in wines made from dried and botrytized grapes.

Sensory effects

It is a substance with a sweet taste (70% of the sweetness of glucose) that can give, when it is present in fairly high quantities, a sensation of mellowness and viscosity to a wine.

Phenolic substances

These are important substances that have an influence on both the visual aspects (the hue) and the gustatory/tactile ones of a wine (structure, body, astringency, bitterness). They are contained in the skins of the grapes and their presence in the wine depends on the extraction and vinification methods used. It is in fact the more or less prolonged contact of the fermenting must with the skins that determine the extent to which these substances pass into the must and then the wine, characterizing its classification both in terms of color (white, rosé, red, deep red) and sensory qualities. Consequently, white wines have a lower polyphenolic content than red wines, with a concentration in the former of between 0.1 and 1 g/l and in the latter of 0.5 and 3.5 g/l.

Phenolic substances may be divided up beween non-flavonoids and flavonoids (see in greater detail below); amongst the latter we find the two main categories, the anthocyanins and the tannins.

Anthocyanins are responsible for the purplish-ruby hue of red wines, while tannins are phenolic compounds with a molecular weight of between 500 and 3000, which have an influence on the gustatory/tactile sensations (astringency, structure), the fixation of color (favoring the formation of anthocyanin/tannin complexes) and the conservation of the wine (as they regulate oxidation-reduction phenomena).

Among the many variables that influence the quality of tannins is, in particular, their origin, because they are contained not only in the skins but also in the stalks and seeds (pips) as well as in the wood of the barrels used for maturation. Those from the stalks and seeds in particular, but also from low-quality barrels or from the skins of unripe grapes can give aggressive (green tannins) and bitter notes (bitter tannins).

Sensory effects

The quantity, type, composition and evolution of polyphenols influence both the visual aspects and the gustatory/tactile ones (structure, body, astringency, bitterness) of a wine.

Depending on their molecular weight (polymerization) and their condensation with anthocyanins and polysaccharides they determine the taste sensations of volume, structure, softness and dryness; if they are excessive or not particularly “noble” they can cause a bitter, astringent flavor (with the taste and aroma of leather).

Mineral salts

These may be salts of potassium, magnesium, calcium or salts of carbonic, sulfuric, and phosphoric acids, etc..

Their presence varies between 1.2 and 4 g/l.

Sensory effects

These give the wines particular depth and especially a fresh, tangy flavor. If they are present together with certain aromatic notes (flint, iron, chalk, petroleum) they accentuate their “mineral” sensations.

Polysaccharides and macromolecules

These are compounds with a high molecular weight that we can find – to a notable degree – in wine when it has been kept for a long time in contact with the lees from the fermentation, because they are to be found mainly in the cell walls of the yeasts.

By means of their autolysis, polysaccharides and other macromolecules are liberated, amongst which are mannoproteins, also obtainable by adding special enzymes (with pectolytic action and β-glucanase).

Their presence varies from 1 to 5 or 6 g/l.

Sensory effects

The influence of these compounds manifests itself during tasting by means of greater softness, roundness and fullness of flavor, contributed to by the lesser astringency, but also during the retronasal phase with a lengthening of the wine’s persistence, even though this may often be compensated for by less intense aromas.