Which acid gives vinegar its characteristic sour taste?

The acid responsible for vinegar’s characteristic sour taste is acetic acid.

Acetic acid, also called ethanoic acid, has the formula CH₃COOH. In household vinegar, it is usually present in a dilute water solution, commonly around 4% to 8% by volume depending on the product and region. Pure acetic acid is a clear liquid with a sharp smell and freezes at about 16.6°C.

Vinegar is produced when acetic-acid bacteria oxidize ethanol in fermented liquids. This process explains why wine, cider, or other alcoholic beverages can develop a vinegar-like character when exposed to oxygen and suitable microbes.

Acetic acid is both a food ingredient and an industrial chemical. It is used to make vinyl acetate, acetate esters, and cellulose acetate. Vinegar’s acidity does not come from acetic acid alone in every recipe, but acetic acid is the defining acid in ordinary vinegar.