The monosaccharide (simple sugar) is also known as fructose or also laevulose. Fructose is formed in grapes only after glucose (grape sugar) and dominates in overripe or noble rot berries. It is one of the sweetest naturally occurring sugars and sweetens up to three times as much as glucose. At the beginning of fermentation it is in the grape must together with the glucose in a ratio of 1:1. Both belong to the so-called hexoses and are together called invert sugar. During the fermentation of grape must, the glucose is preferably converted into alcohol and carbon dioxide, this is called glucophilic behaviour of the yeasts. This is why fructose dominates the residual sugar in the wine. In contrast to glucose, fructose can be broken down by the human body in the case of diabetes (sugar disease). This explains why fructose has long been used as a useful substitute for sucrose and glucose in the dietary treatment of diabetics. However, this assessment has changed due to new findings. See diabetic wine.
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