The colourless liquid (also known as acetylic acid, ethanoic acid, glacial acetic acid, ethane acid) is one of the most common organic compounds in food. In the form of vinegar it was discovered earliest among all acids and was already well known to the Egyptians, Babylonians and Chinese in ancient times. Undiluted acetic acid has a strongly corrosive effect on the skin. It is relatively easy to recognise by its characteristic vinegar smell, which is particularly noticeable when diluted. Even after extensive dilution, the taste is still distinctly acidic. It is the most frequently occurring volatile acid in wine. Healthy wines have a proportion of 0.15 to 0.5 g/l, particularly sensitive tasters complain about a wine already from 0.6 to 0.7 g/l. Above this amount, this indicates spoilage or acetic acid sting, which is considered a serious wine defect.
Acetic acid is formed during fermentation by Acetobacter (acetic acid bacteria) by oxidation of alcohol via the intermediate product acetaldehyde. Colloquially this is also called acetic acid fermentation. However, this is not a fermentation, but an oxidative metabolic process or a so-called fermentation. Acetic acid bacteria can also enter the grape must with infected grape material. The reaction of acetic acid with alcohol during fermentation also produces ethyl acetate, which in excessive quantities can lead to the wine defect uhutone (typical acetone smell). Another aromatic compound is acetic acid isoamyl ester. The total amount of all volatile acids contained in wine is indicated as acetic acid. Different maximum limits apply depending on the type of wine: