Vinegar, which is essentially any alcoholic liquid that has had too much exposure to air, was almost certainly an accidental discovery that must have been a shock to the palate of the person who found that his or her wine or beer had gone bad. The wine or beer may have been "ruined," but the liquid into which it was transformed has played an important role in cuisines around the world. All vinegars have a sour flavor, but depending on what liquid the vinegar was fermented from, there are a number of subtle differences between them.
Any liquid containing sugar or starch can become vinegar (the name means "sour wine" in French); it has been fermented using dates, sugar cane, raspberries, blueberries, and a large variety of other fruits. The most popular of these is probably cider vinegar, made from fermented apple cider. The Japanese make frequent use of a lightly flavored rice-wine vinegar in their cooking; our recipe for a refreshing cucumber salad includes this type of vinegar.
The British are known for their mild malt vinegars, derived from a hop-free beer, and one specialty of the Italians is the pungent balsamic vinegar, made from crushed grapes that ferment in wooden casks for decades or even centuries.
Two commonly used vinegars are red- and white-wine vinegar. White-wine vinegar is perfect for mild salad dressings or as a base for flavored vinegar, made by adding fruit or fresh herbs. Vinegar made from red wine has a more robust flavor than the white, and is often used as a marinade ingredient or in vinaigrette.
Vinegar should be stored in an airtight container in a cool, dark place. It will usually maintain its flavor for six months, but should be discarded at the first sign of mold.