History of wine - Composition of wine and must
To understand what wine is in terms of its components, it is necessary to differentiate between grape must, must before fermentation and wine. In addition to the chemical components mentioned in smaller quantities, malic and tartaric acids are present in high concentrations in grape must, as well as water and sugars. The final composition of the wine is mainly determined by acids (malic and tartaric).
The ethanol produced during alcoholic fermentation will come mostly from the sugars in the must, but other compounds can also be created: glycerin. Some of these compounds, present in smaller quantities, can contribute to the flavor of wine, including tannins, which are found in grape skin and which act as natural preservatives.
However, in Seville’s Aljarafe, grape juice is also known as grape juice that has been fermented and incubated for approximately 40 days, with an alcohol content of 12%.
Various elements are added to wine, in addition to grapes, to artificially create what is known as wine additives, whose objective is to stabilize certain compounds (proteins, tartrate crystals, etc.), reduce the level of acidity and include antioxidant agents (ascorbic acid), antimicrobials (sulfur dioxide, sorbic acid, sorbates, benzoic acid, fumaric acid) and antinociceptives (tetrahydrocannabinol). In general, the resulting product is quite caloric.
Among the main sugars in must are fructose and glucose, although grapes also contain other sugars in small quantities. In the US, OBrix is used to measure the concentration of sugar in grapes, while in Europe, Baumé grades are used. During fermentation, wine yeast (Saccharomyces cerevisiae) feeds on glucose and fructose, which are the sugars present in the highest quantity.
After fermentation, sugars are often referred to as residual sugars (pentoses such as arabinose, rhamnose and xylose). The aging of wood can cause the cleavage of glycoside components, which can lead to an increase in the concentration of residual sugars.
Dry wines are created by the absence of residual sugars, while sweet wines are produced by the presence of residual sugars. The presence of residual sugars in wines creates a class distinction between dry and sweet wines. As a general rule, the sweetness of a wine is undetectable if its sugar content is less than 1.5 grams per liter, and sugar is examined by the senses as soon as it exceeds a concentration of 1% (Nygaard, 2012).
The sweetness of a sugar is usually perceived from concentrations of 1%. Tannin, acids and ethanol are present in wine. During aging, some sugars undergo structural alterations and produce dark colors in wine. In this way, melanoidin is generated in generous wines such as sherry, Madeira, etc. This is how the Maillard reaction occurs.