Alcoholic fermentation

The process by which certain microorganisms — mainly yeasts — metabolise sugars anaerobically to produce alcohols: glucose is converted to pyruvic acid, decarboxylated to acetaldehyde, and the acetaldehyde reduced to ethanol, releasing carbon dioxide. A wide variety of substrates serve, from grain for beer to grapes and other fruits for wine, though the constituent sugars must first be freed from starch or cell walls. Brewers harvest the ethanol, bakers rely on the carbon dioxide to raise dough, and flavour congeners formed alongside define each beverage’s character. It is biotechnology’s oldest industrial process.