Does Vinegar expire?

Acetic acid at the concentration in table vinegar — around 5% — is hostile to essentially everything that causes spoilage, which is why vinegar is a preservative in its own right. White distilled vinegar is stable indefinitely and does not change appreciably. Cider, wine and malt vinegars contain more organic material, so they darken, throw a sediment, or grow a cloudy gelatinous raft of cellulose and acetic acid bacteria known as a mother. That mother looks alarming and is entirely harmless; strain it out or leave it in.

How to store it

• Cool, dark, tightly capped. Light and air fade colour and flavour.

How to tell it has gone

• Cloudiness and a floating mother are normal. Anything smelling of solvent rather than vinegar has been contaminated.

"Use by" and "best before" are legally different. Use-by is a safety date and should be respected; best-before is about quality, and food is usually fine well past it. Where the two diverge matters, the page above says which applies.