The monosaccharide (Plain sugar) is better known under the term dextrose or dextrose. This type of sugar is first formed in the grapes. In the winemaking at the beginning of the fermentation she is with the fructose (Fructose) in a one to one ratio grape, Both types of sugar are so-called hexoses and are together as invert sugar designated. They are very different in sweetness, fructose sweetens about two and a half times as strongly as glucose. Glucose in is preferred for fermentation alcohol and carbon dioxide converted. That is why fructose dominates in residual sugar of wine. Unlike fructose, glucose can diabetes (Diabetes) cannot be broken down by the human body or only with difficulty.
French scientist Louis Pasteur (1822-1895) reported in 1861 that yeasts in aerobic Environment (that means presence of oxygen ) much less during fermentation sugar consume than in anaerobic environment. With higher amounts of glucose in grape must from about 100 mg / l can also under aerobic conditions alcohol be formed. According to the English biochemist Herbert Grace Crabtree, this is called Crabtree effect or also referred to as the "glucose effect". With small amounts of glucose breathe yeasts in the presence of oxygen, the sugar directly, so it is not converted into alcohol.
In the research institute Geisenheim there are attempts to use the enzyme The glucose in the grape must in gluconic convert and thereby reduce the sugar. The yeast cannot convert gluconic acid into alcohol. This should make it possible to target wines with balanced Produce alcohol to improve taste. See under alcohol reduction,