According to About.com, bacteria in the form of a culture is introduced into the chosen liquid. The liquid is then fermented, allowing the bacteria to break down the ethanol into byproducts, the main byproduct being acetic acid. Vinegar is usually pasteurized before it is sold to kill off the bacteria that caused fermentation. Vinegar that is not pasteurized is called raw vinegar.
Other substances found in vinegar include vitamins, minerals and flavor compounds. Vinegar is used in cooking for the tart flavor it adds to food.Learn more about Food Facts