History of wine - Composition of wine and must (4)
During the maturation process, alcohols react with natural grape acids to form esters (esterification). Enzymatic esterification is the type of esterification that occurs most frequently in wine and represents about 160 functional groups.
Esters are generally classified into two categories: those formed by enzymatic actions (butanoate, exanoate) and those created chemically by esterification. Because of their importance when it comes to providing bouquets, they are the most common functional group in wines.
There are several types of esters, besides fruit fragrances, that can be detected during wine tasting. Although there are different types of esters for wine tasting, volatile and non-volatile esters are the most significant. Ethyl acetate is one of the most important volatile esters in wine.
Within a certain range, ethyl acetate is undetectable to most people. Many young wines contain higher levels of esters. The threshold for each ester is below which most people cannot detect it.
Proline and arginine concentrations vary greatly in grapes of different varieties, where proline is an important component of nitrogen metabolism in yeasts. Proline is a key component of nitrogen metabolism in yeasts, which is why increases in proline/ arginine ratios vary significantly in the different varieties of Vitis vinifera.
The glutamine/alanine group is the second most important class of amino acids. After fermentation, the amino acid content is reduced, since most of them enter the metabolism of yeast in one way or another.
Approximately 100 mg/L to 840 mg/L of proteins are found in the must. During fermentation, the protein content can be reduced by almost 40%. Proteins work like zwitterions, in some cases they can coagulate and create instability in wine. The objective of clarification is to eliminate these unstable proteins from wine. One of the most commonly used agents is bentonite and the other is silica gel.