Acetic fermentation

Slightly fermented liqueurs become sour when exposed to air. This is due to the conversion of alcohol to acetic acid. Acetic acid is produced by fermenting various substrates (starch solution, sugar solutions or alcoholic foods such as wine or cider) with Acetobacter bacteria. Examples of acetic acid fermentation:

• Western Europe: cider and wine vinegar, kambucha
• Africa: palm wine vinegar
• Philippines: coconut water vinegar

What is vinegarAcetobacter aceti, which is normally used to make vinegar, can produce vinegar with up to 14 per cent acetic acid. If cider, wine or malt is used as the starting material, around 5% acetic acid is produced. The colour and flavour of the vinegar will depend on the source (cider, wine, beer, barley malt) and the method of production. Traditionally, vinegar was made in barrels filled with wood shavings and sprayed with wine. When vinegar is distilled, it has no colour.

Legislation in many countries requires the acetic acid in vinegar to be produced by fermentation rather than chemical processes. There are three chemical processes to produce acetic acid: methanol carbonylation, butane oxidation or acetaldehyde oxidation. Vinegar contains 4-8% acetic acid by volume.