Viruses, Bacteria, Protists, and Fungi

What is the role of yeast in beer production?

Beer is made by fermenting water, malt, sugar, hops, yeast (species Saccaromyces), salt, and citric acid. Each ingredient has a specific role in the creation of beer. Malt is produced from a grain—usually barley—that has sprouted, been dried in a kiln, and ground into a powder. Malt gives beer its characteristic body and flavor. Hops is made from the fruit that grows on the herb Humulus lupulus (a member of the mulberry family) The fruit is picked when ripe and is then dried; the ingredient gives beer a slightly bitter flavor. Yeast is used for the fermentation process.

Making beer is a complex process. One method begins by mixing and mashing malted barley with a cooked cereal grain such as corn. This mixture called “wort,” is filtered before hops is added to it. The wort is then heated until it is completely soluble. The hops is removed, and after the mixture is cooled, yeast is added. The beer ferments for 8 to 11 days at temperatures that range between 50°–70°F (10°–21°C). The beer is then stored and kept at a state that is close to freezing. During the next few months the liquid takes on its final character before carbon dioxide is added for effervescence. The beer is then refrigerated, filtered, and pasteurized in preparation for bottling or canning.


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