Sweet tasting, crystalline food, which is obtained from various plants such as sugar cane or sugar beet. Depending on the number of carbon atoms in a sugar molecule, there are the terms pentoses (5 atoms = chemical formula beginning with C5) and hexoses (6 atoms = C6). In the metabolism of the human body, the sugars are oxidized, which releases energy when heat is released, which in turn causes motor functions. Most plants produce sugar by photosynthesis in the form of sucrose and store it in the cells. Some is converted into starch and stored in the stem and roots.
Other plants, such as the grapevine, break down sucrose into its components glucose (glucose) and fructose (fructose) and store them in the grapes' berries. Both types of sugar are so-called monosaccharides and belong to the group of hexoses. During fermentation, they are directly converted to 90% into ethanol and carbon dioxide, whereby this occurs more quickly with glucose. Fructose sweetens many times more than glucose and also dominates the residual sugar. The arabinose, rhamnose, ribose and xylose belonging to the pentoses are not or hardly fermentable and remain as residual sugar.
In grape must there are also traces of higher-value sugars (multiple sugars), the disaccharides. These include cane sugar and beet sugar (chemically identical), also known as sucrose. In contrast to fructose and glucose, they are first broken down by the enzyme invertase into their building blocks fructose and glucose and only then are they converted into alcohol and carbon dioxide. As a rough rule of thumb, fermentation results in 0.66% vol alcohol content from 10 g sugar in 1,000 g must. As a rule, white wine has an alcohol content of 16.5 g/l and red wine 18 g/l of sugar, giving an alcohol content of 1.0% vol (see a conversion table under must weight).
However, it should be noted that the sugar in the must never ferments completely, but always remains a residual sugar. In sweet wines a relatively high sugar content is given by premature end of fermentation. Sugar in various forms may be used for enrichment (increasing the alcohol content in unfinished wine) and sweetening (increasing residual sugar in finished wine) in compliance with the legal regulations applicable in the respective countries. Sugar is an essential, qualitative component of the must or, depending on the type of wine, of wine. The phenomenon that the subjective perception of sweetness in wine can differ greatly from the analytical values is described under the keyword sweet. Regarding the other ingredients in the wine, see under total extract. See also under ICUMSA and reducing sugars.
Complete lists of the numerous vinification measures or cellar techniques, as well as the various types of wine, sparkling wine and distillate regulated by wine law are included under the heading "Vinification". Comprehensive information on wine law can be found under the keyword wine law.