A beer is any of a variety of alcoholic beverages produced by the fermentation of starchy material derived from grains or other plant sources. The production of beer and some other alcoholic beverages is often called brewing.
Historically, beer was known to the Sumerians, Egyptians, and Mesopotamians, and dates back at least as far as 4,000 BC. Because the ingredients used to make beer differ from place to place, beer characteristics (type, taste, and color) vary widely.
Typically, beers are made from water, malted barley, and hops, fermented by yeast. The addition of other flavorings or sources of sugar is not uncommon.
Because beer is composed mainly of water, the source of the water and its characteristics have an important effect on the character of the beer. Many beer styles were influenced or even determined by the characteristics of the water in the region.
Among malts, barley malt is the most often and widely used owing to its high enzyme content but other malted and unmalted grains are widely used, including wheat, rice, maize, oats, and rye.
Hops are a relatively recent addition to beer, having been introduced only a few hundred years ago. They contribute a bitterness that balances the sweetness of the malt and have a mild antibiotic effect that favors the activity of brewer’s yeast over less desirable organisms.
Yeast, in a process called fermentation, metabolize the sugars extracted from the grains, producing many compounds including alcohol and carbon dioxide. Dozens of strains of natural or cultured yeasts are used by brewers, roughly sorted into three kinds: ale or top-fermenting, lager or bottom fermenting, and wild yeasts. The scientific name for brewer’s yeast is Saccharomyces cerevisiae, an important model organism in molecular and cell biology.
One pint (568 ml) of beer typically contains about two units of alcohol, although alcohol content can vary significantly with style and brewer.
