Brewing methods

Beer is produced through steeping a starch source (commonly cereal grains) in water and then fermenting with yeast. Brewing has taken place since around the 6th millennium BC, and archeological evidence suggests that this technique was used in ancient Egypt. Descriptions of various beer recipes can be found in Sumerian writings, some of the oldest known writing of any sort. Brewing is done in a brewery by a brewer, and the brewing industry is part of most western economies.

The methods used to produce beer may be unique to a beer style, geographic region, or company.

Barrel aging

Beers are sometimes aged in barrels to achieve a variety of effects in the final product. Sour beers such as lambics are fully fermented in wood (usually oak) barrels similar to those used to ferment wine, usually including microflora other than Saccharomyces cerevisiae.

Other beers are aged in barrels which were previously used for maturing spirits. Stouts (particularly Russian Imperial Stouts) are sometimes aged in bourbon barrels. Goose Island's Bourbon County Stout was one of the first bourbon barrel-aged beers in the U.S., but the method has now spread to other companies, who have also experimented with aging other styles of beer in bourbon barrels.