A chemical change induced by a living organism or enzyme, specifically bacteria or the microorganisms occurring in unicellular plants such as yeast, molds, or fungi. The reaction usually involves the decomposition of sugars and starches to ethanol and carbon dioxide, the acidulation of milk, or the oxidation of nitrogenous organic compounds. The basic reaction is catalyst C6H12O6 → 2C2H5OH + 2CO2 Enzymes are usually involved in such reactions; with yeast, the effective enzyme is zymase. Fermentation is essential in the preparation of breads and other food products and in the manufacture of beer, wine, and other alcoholic beverages, as well as of citric acid, gluconic acid, sodium gluconate, and synthetic biopolymers. Much of the industrial alcohol used in the U.S. is made by fermentation of blackstrap molasses, a by-product of sugar manufacture. Antibiotics are produced by various forms of microorganisms active in molds, especially bacteria and actinomycetes. The activated sludge process for sewage digestion is a form of fermentation. A continuous fermentation process for deriving edible protein from petroleum has been introduced. Fermentation is also used in making synthetic amino acids. Research in this field is being directed toward conversion of agricultural, urban, and animal wastes to fuels by fermentation processes.See Yeast; Sewage Sludge; Antibiotic; Bacteria; Biotechnology.
