How to Know When Wine Has Gone Bad. Before drinking any wine, it is wise to check the wine for signs that it has gone bad. Bad wine is not defined as wine that simply doesn't taste good; rather, it is wine that has had chemical changes take place that actually make the wine not good to drink. Follow these steps to help you know when wine has gone bad.
Smell the wine for signs of oxidation, which occurs when air has gotten into a bottle of wine. Open bottles of wine that have not been stored properly can easily become oxidized and will smell pungent, like vinegar. This smell is easily recognizable
Look for signs of corked or corky wine. When wine is bottled, the natural cork used in bottling wine can sometimes get wet. If the cork gets wet, it can develop an invisible mold. When the moldy cork is then placed into the wine bottle, the mold actually goes into the wine itself. This will give the wine a musty or cardboard like odor. The wine may even smell like the cork itself.
Sniff the wine for a sulfur odor. Wine that has too much sulfur in it can smell like matchsticks or rotten eggs. Wine can have too much sulfur in it due to improper storage or because too much sulfur dioxide was added during the bottling process.
Check for signs of cooked wine. If wine is stored in warm or hot places such as attics, car trunks or near the stove, it can begin to cook. Cooked wine will have a brownish tint when poured into a glass. It can also smell caramelized. Bottles of cooked wine may also have corks that appear pushed upwards and partially out of the wine bottle.