Fermented Beverages

Yeasts have been used since ancient times to brew alcoholic beverages such as wine, beer, whisky, brandy and rum; zymology is the applied science that studies the biochemistry of fermentation and its practical uses. Saccharomyces cerevisiae (brewer's yeast) ferments malted cereals and fruit juices into a range of drinks — wine and beer are produced by fermentation alone, while whisky, brandy and rum additionally undergo distillation. Wine-making (oenology) ferments grape juice with strains of S. cerevisiae; red wine is fermented with the skins and sometimes stems of black grapes, while white wine uses only the juice, without skins or stems, of white or red grapes. Beer is brewed from germinated barley malt using Saccharomyces carlsbergensis or S. cerevisiae; rum comes from fermented sugarcane juice or molasses; whisky is distilled from a fermented grain mash, all typically using S. cerevisiae. In parts of South India, sap tapped from unopened coconut or palm spadices — pathaneer — ferments naturally, with the help of wild yeasts, into toddy, a mildly alcoholic drink (about 4% alcohol) that turns unpalatable within about 24 hours and is then used to make vinegar; boiling fresh pathaneer instead yields jaggery or palm sugar. On an industrial scale, S. cerevisiae is the chief producer of ethanol (C2H5OH) used as industrial, laboratory and fuel alcohol; bacteria such as Zymomonas mobilis and Sarcina ventriculi also ferment ethanol. Starchy feedstocks like molasses, corn, potatoes or wood waste are first milled and treated with dilute or fungal amylase (from Aspergillus) to release fermentable sugars, which yeast then converts t …