Acetic acid is formed when common airborne bacteria interact with the alcohol present in fermented solutions such as WINE, BEER or CIDER. Acetic acid is the constituent that makes vinegar sour. Acetic acid has been produced and used by humans since before the dawn of recorded history. Vinegar is formed from dilute solutions of alcohol, such as wine, by the action of certain bacteria in the presence of oxygen. These bacteria require oxygen, and the overall chemical change is the reaction of ethanol with oxygen to form acetic acid and water. Acetic acid is a clear, colorless liquid with a sharp, irritating odor of vinegar. The chemical compound acetic acid (from Latin acetum, meaning "vinegar"), or more properly ethanoic acid, is the acid that gives vinegar its sour taste. Acetic Acid is often used as a drying agent in packaged foods to extend shelf life. Acetic acid is used as a food additive, as a photographic chemical, in the manufacture of plastics the primary use of acetic acid is used in the manufacture of cellulose acetate for films and plastic goods; about 75 percent of the acetic anhydride produced annually in the United States is used for this purpose. Approximately 1.5 percent of the annual acetic anhydride production is used in the synthesis of aspirin. Other uses include the manufacture of industrial chemicals, pharmaceuticals, perfumes, plastics, synthetic fibers, explosives, and weed killers. Because acetic anhydride reacts with water, it is sometimes used as a dehydrating agent in reaction mixtures where removal of water is necessary.