Definition - What does Alcoholic Fermentation mean?
Alcoholic or ethanol fermentation is the transformation of natural grape sugars into ethanol and carbon dioxide, which turns grape juice into wine. The process of alcoholic fermentation begins shortly after harvest, when large bins of grapes are pressed or crushed to release their juice, making a must. The natural sugars in the must mix with the natural yeast on the grape skins, and alcoholic fermentation begins naturally, however, winemakers add different strains of yeast to the must depending on the style of wine they are making.
WineFrog explains Alcoholic Fermentation
Alcoholic fermentation is the magical biological process that turns grape juice into wine. While we commonly know that during fermentation yeast covert sugar into alcohol, not all types of fermentation will result in alcohol, like in the case of sauerkraut. This is because cabbage doesn’t contain the high amounts of sugars that grapes do, and as a result, the actual process of the fermentation is different. Alcoholic fermentation is an anaerobic process that requires the presence of glucose and yeast.
As the yeast eat the sugar, a complex enzymatic process occurs; the glucose is converted into lactic acid and pyruvic acid. Two enzymes, pyruvate decarboxylase and alcoholic dehydrogenase, specifically convert the pyruvic acid into ethanol and carbon dioxide. In order for this to happen, the fermentation takes place in a closed cask or tank with a one-way valve to allow the carbon dioxide to escape while preserving the ethanol.
The fermentation has to be closed, as oxygen prevents ethanol from being made. It also prevents other yeast and bacteria from entering the fermentation process, which would spoil the wine. The carbon dioxide is released, or in the case of sparkling wine, controlled, as it builds up pressure that could make the cask or tank explode. In sparkling wine, the carbon dioxide is what creates the effervescence. Alcoholic fermentation is complete when all of the sugar has been consumed by the yeast, however, winemakers can stop the fermentation prior to that by using additives or by cooling the wine down, this would be done to leave residual sugar in the wine to create a specific taste and flavor profile.