Vinegar is acidic. It has a pH of about 2.2, making it just slightly less acidic than lemon juice. The primary ingredients in vinegar are water and acetic acid, which is produced by the fermentation of ethanol by acetic acid bacteria.
The formation of vinegar occurs naturally when fruit juice remains in contact with oxygen for an extended period of time. An uncorked batch of wine or uncooked apple juice will turn into vinegar in about a week. In addition to its culinary uses, vinegar can be used for cleaning and disinfecting and is an excellent preservative. Vinegar needs no refrigeration and has a virtually unlimited shelf life.