The principle of wine fermentation is that the sugar in the grape juice is converted to alcohol by the action of yeast to become wine. Therefore, generally speaking, the higher the sugar content in the grapes, the higher the alcohol content in the wine.
Wine is made by collecting and pressing grapes. There are hundreds of different grape varieties. Once the grapes are crushed, the combination of the natural sugars in the grapes and the yeast (which is naturally present on the skins and can be replenished by the winemaker) leads to fermentation to produce alcohol.
Alcohol fermentation is the process of converting natural glucose into ethanol and carbon dioxide, and converting grape juice into wine. Alcohol fermentation begins shortly after harvest. When large quantities of grapes are pressed or crushed to release the juice, the natural sugars in the juice mix with the natural yeast on the grape skins and alcohol fermentation naturally begins. However, winemakers add different types of yeast to the juice depending on the style of wine.
When yeast eats sugar, it goes through a complex enzymatic process. Glucose is converted to lactic acid and pyruvic acid. Pyruvate decarboxylase and ethanol dehydrogenase are two enzymes that specialize in converting pyruvate to ethanol and carbon dioxide. For this purpose, fermentation is carried out in a closed barrel or tank with a check valve that releases carbon dioxide while preserving ethanol.
