Most important carboxylic acid (CH3COOH). Pure (“glacial”) acetic acid is a clear, syrupy, corrosive liquid that mixes readily with water. Vinegar is its dilute solution, from fermentation and oxidation (see oxidation-reduction) of natural products. Its salts and esters are acetates. It occurs naturally as a metabolic intermediate in body fluids and plant juices. Industrial production is either synthetic, from acetylene, or biological, from ethanol. Industrial chemicals made from it are used in printing and as plastics, photographic films, textiles, and solvents.
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The acetic acid bacteria are found in nature where ethanol is being formed as a result of yeast fermentation of sugars and plant carbohydrates. They can be isolated from the nectar of flowers and from damaged fruit. Other good sources are fresh apple cider and unpasteurized beer which has not been filter sterilized. In these liquids the acetic acid bacteria grow as a surface film due to their aerobic nature and active motility. Vinegar is produced when acetic acid bacteria act on alcoholic beverages such as wine.
Some genera, such as Acetobacter, can eventually oxidize acetic acid to carbon dioxide and water using Krebs cycle enzymes. Other genera, such as Gluconobacter, don't further oxidize acetic acid, as they do not have a full set of Krebs cycle enzymes.