Vinegar is produced when bacteria convert the alcohol in a liquid into acetic acid.

The longer version

Turning alcohol into vinegar is a two-stage biological process. Yeast first converts sugars into ethanol, and then a group of acetic acid bacteria oxidizes that ethanol into acetic acid using oxygen from the air. Because the bacteria need oxygen, traditional methods rely on large surface areas, trickling the liquid over wood shavings or leaving it in partly filled vessels.

Once acidity climbs, the environment becomes hostile to most other organisms, so the liquid keeps. The raw material shapes the result: cider, wine, malt, and rice each yield a vinegar with its own residual flavor notes. A cloudy film on the surface is often the bacterial culture itself.

Where this entry sits

Everyday ingredients turn out to be full of quiet chemistry and long history. This collection gathers short, plain explanations of how bread rises, why onions sting, where common spices originate, and how coffee, tea, and chocolate reached the modern kitchen. The full list sits on the Food and Drink page, where every entry is listed in order.