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Glucose

glucosa (ES)
glucosio (I)
glucose (PO)

The monosaccharide (simple sugar) is better known as grape sugar (dextrose). This type of sugar is formed first in the grapes. At the beginning of fermentation, it is found in the grape must with fructose (fruit sugar) in a ratio of one to one. Both types of sugar belong to the hexoses and are together called invert sugar. They are very differently sweet, fructose is about two and a half times sweeter than glucose. During fermentation, glucose is preferentially converted into alcohol and carbon dioxide. This is why fructose dominates in the residual sugar of the wine. In contrast to fructose, glucose cannot or can only with difficulty be broken down by the human body in diabetes (diabetes).

Weintraube - Inhaltsstoffe (Zucker, Säuren, Phenole, Aromastoffe)

The French scientist Louis Pasteur (1822-1895) recognised through experiments as early as 1861 that yeasts in an aerobic environment (presence of oxygen) consume much less sugar during fermentation than in an anaerobic (absence of oxygen) environment. However, at higher glucose levels in the grape must from about 100 mg/l, alcohol can also be formed under aerobic conditions. This is called the Crabtree effect (also Pasteur effect, glucose effect) after the English biochemist Herbert Grace Crabtree. With small amounts of glucose, the yeasts breathe the sugar directly in the presence of oxygen, so it is not converted into alcohol.

At the Geisenheim Research Institute (in the Rheingau region of Hesse), there are attempts to convert the glucose in the grape must into gluconic acid by means of the enzyme glucose oxidase, thus reducing the sugar. This is because the gluconic acid cannot be converted into alcohol by the yeasts. This should make it possible to produce wines with a balanced alcohol content in order to improve the taste. See under alcohol reduction.

Grape berry with ingredients: By Mariana Ruiz Villarreal(LadyofHats), Public domain, Link

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Dr. Christa Hanten

For my many years of work as an editor with a wine and culinary focus, I always like to inform myself about special questions at Wine lexicon. Spontaneous reading and following links often leads to exciting discoveries in the wide world of wine.

Dr. Christa Hanten
Fachjournalistin, Lektorin und Verkosterin, Wien

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