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).

Increased amounts of volatile acids in wine - of which acetic acid is by far the main component - are considered wine faults once the perception threshold is exceeded; acetic souring thus represents the clearly perceptible final stage of increased volatile acids. Depending on the type of wine, volatile acids often become noticeable from around 0.8 to 1.2 g/l acetic acid due to clearly negative taste and odour notes.
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Markus J. Eser
Weinakademiker und Herausgeber „Der Weinkalender“