Volatile Acidity (VA)

Acetic acid bacteria (Acetobacter) convert ethanol to acetic acid (vinegar) and ethyl acetate (nail polish remover) in the presence of oxygen. Can also be produced by wild yeasts during fermentation. All wines contain trace VA; it becomes a fault when perceptible as vinegar.

Sharp, vinegar-like acidity in the nose and palate. At low levels, ethyl acetate smells like nail polish remover or model glue. Slightly elevated VA can lift aromatics in some wines (Amarone, Sauternes), but beyond 0.6-0.8 g/L acetic acid, it's universally considered a fault.

Minimizing oxygen exposure, maintaining adequate SO2, keeping vessels full (minimal headspace), controlling fermentation temperatures, and strict cellar hygiene. Avoid leaving wine on gross lees in warm conditions.