A common wine defect (also known as acetic acid taint, volatile acidity) caused by excessive amounts of acetic acid in the wine. The starting point is acetobacter (acetic acid bacteria), which form on grapes in the vineyard, cause vinegar rot and enter the grape must through contaminated grapes (picture left).
The vinegar fly (pictured right) also plays a role in the transmission and spread in the vineyard. Acetic acid bacteria form acetic acid from alcohol via the intermediate product acetaldehyde. Lactic acid bacteria can also be the cause. Incompletely filled wine containers with an empty space favour the process of acetic acid formation through the influence of oxygen. The acetic souring occurs most frequently during the mash fermentation of red wines because the relatively high amount of oxygen in the mash intensifies the process.
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Egon Mark
Diplom-Sommelier, Weinakademiker und Weinberater, Volders (Österreich)