Which chemical compound is the main acid in vinegar?

The chemical compound that is the main acid in vinegar is acetic acid.

Acetic acid, also called ethanoic acid, has the formula CH₃COOH. It gives vinegar its characteristic sour taste and sharp smell. Household vinegar is usually a dilute aqueous solution containing roughly 4% to 8% acetic acid, though concentrations vary by product and regulation.

Vinegar forms when microorganisms convert ethanol into acetic acid in the presence of oxygen. This process has been used for thousands of years in food preservation and fermentation. Pure acetic acid freezes at about 16.6°C, so it can form ice-like crystals in cool conditions and is sometimes called glacial acetic acid.

Citric acid is prominent in citrus fruits, formic acid occurs in ant venom, and lactic acid forms during certain biological processes. These acids are not the defining acid of ordinary vinegar.