How Can You Tell an Opened Bottle of Wine Has Spoiled?

The fastest way to tell an opened bottle of wine has spoiled is by smell and taste: fresh wine carries notes of grape, fruit and light alcohol, while spoiled wine gives off a sharp smell closer to vinegar or wet cardboard. This shift comes from the wine oxidizing after prolonged contact with air. What changes in color and appearance?Red wine gradually turns a dull, brownish color over time; white wine darkens toward a honey shade as it yellows. A thin, foamy layer forming on the surface when poured into a glass is also a sign unwanted fermentation has started. A close look at the bottle's neck may reveal small white or brownish crystals; these are usually harmless tartrate crystals and not a spoilage sign. What actually matters is cloudiness and dullness in the liquid itself. How does the taste change?Fresh wine has a balanced tartness; in spoiled wine that tartness turns into a sharp vinegar taste that burns going down. If the fruity, full flavor gives way to a flat, lifeless taste, the wine is no longer fit to drink — though it can still be used in a sauce or a vinegar-based recipe. A slight fizz on the tongue is another spoilage sign; unexpected carbonation in a still wine means an unwanted second fermentation has started in the bottle. How does storage time affect spoilage?An opened bottle of red wine, recorked and kept in the fridge, should generally be finished within 3-5 days; for white and sparkling wines that window drops to 3-4 days. Going past that doesn't make the wine dangerous, but it noticeably ruins the flavor. The less contact wine has with air, the more slowly it spoils; that's why decanting half of a large bottle into a smaller one reduces the air gap above the remaining liquid and slows spoilage. Vacuum wine stoppers serve the same purpose. There's also a difference between red and white: reds, with their higher tannin content, spoil a little more slowly than whites thanks to that compound's natural preservative effect. So a red wine stored under the same conditions can outlast a white by a day or two. Storing an unopened bottle on its side is often recommended, but that no longer matters once it's open; an opened bottle should always stand upright in a cool spot. Keeping it away from light matters too; an open bottle sitting in sunlight on the kitchen counter spoils faster than the same bottle stored in a dark cabinet. Using wine for cooking before its drinking window runs out, depending on the type, avoids waste and lets a wine that has started to fade slightly still add depth to a dish. In short, a vinegar smell, a dull brownish color, foaming, and a flattened taste — together or on their own — mean the opened bottle of wine has spoiled; that wine is no longer for drinking, but it can still be put to use in cooking.