The monosaccharide (Simple sugar) is better known by the term dextrose or dextrose. This sugar species is first made in the grapes. In the winemaking at the beginning of the fermentation she is with the fructose (Fructose) in the ratio of one to one in the grape, Both sugars are among the so-called hexoses and be together as invert sugar designated. They are very different sweet, fructose sweetens about two and a half times as strong as glucose. During fermentation, glucose is preferred alcohol and carbon dioxide converted. Therefore, fructose dominates in the residual sugar of the wine. In contrast to fructose, glucose can be found in diabetes (Diabetes) from the human body is not or only with difficulty degraded.
The scientist Louis Pasteur (1822-1895) already reported in 1861 that yeasts in aerobic Environment (presence of oxygen) during fermentation much less sugar consume as in an anaerobic environment. At higher glucose levels in grape must from about 100 mg / l can but also under aerobic conditions alcohol be formed. This will be after the English biochemist Herbert Grace Crabtree as Crabtree effect or also referred to as "glucose effect". At low glucose levels, the respiratory system will 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 by means of the enzyme Glucose oxidase glucose in grape must gluconic to convert and thereby reduce the sugar. The gluconic acid can not be converted into alcohol by the yeasts. This should make it possible to target wines with balanced To produce alcohol content to improve the taste. See under alcohol reduction,