Can wine turn to vinegar?

Wine turning to vinegar isn't just an old saying — it's real chemistry. The process is called acetic acid fermentation, and it's actually the same reaction used to make high-quality wine vinegar on purpose.

Here's what happens: Acetobacter bacteria (naturally present in the air) land on wine that's exposed to oxygen. They feed on the alcohol and convert it to acetic acid — vinegar. The chemical equation is simple: ethanol + oxygen → acetic acid + water. This is why sealed, properly stored wine never turns to vinegar. The bacteria need air to work.

The risk factors are straightforward: a dried-out or faulty cork that lets air seep in; an open bottle left on the counter for several days; storage above 25 °C (warmth speeds up bacterial activity); and wines with very low sulphite levels, which have less antimicrobial protection.

You can spot the early signs: a sharp, vinegary smell or a nail-polish-remover tang (that's ethyl acetate, a related compound). In advanced cases, you might see a thin, white film on the wine's surface — that's the 'mother of vinegar,' a bacterial biofilm. Once you smell it clearly, the process is well underway and irreversible.

Prevention is straightforward: store bottles properly (lying down, 12-14 °C, 70% humidity), re-cork immediately after pouring, use a vacuum pump for half-finished bottles, and refrigerate open wine. Natural wines (without added sulphites) are especially vulnerable and should be finished within a day or two of opening.

One reassuring note: vinegary wine won't make you sick. If a bottle has turned, use it for cooking — it makes excellent salad dressing or deglazing liquid.