Brewing is the production of beer by steeping a starch source (commonly cereal grains) in water and fermenting the resulting sweet liquid with yeast. It may be done in a brewery by a commercial brewer, at home by a homebrewer, or by a variety of traditional methods such as communally by the indigenous peoples in Brazil when making cauim.[1] Brewing has taken place since around the 6th millennium BC, and archaeological evidence suggests that emerging civilizations including ancient Egypt[2] and Mesopotamia brewed beer.[3] Since the nineteenth century the brewing industry has been part of most western economies. The basic ingredients of beer are water and a fermentable starch source such as malted barley. Most beer is fermented with a brewer's yeast and flavoured with hops.[4] Secondary starch sources (adjuncts), such as maize (corn), rice, or sugar, may also be used.[5] Less widely used starch sources include milletsorghum and cassava.[6] The amount of each starch source in a beer recipe is collectively called the grain bill. Steps in the brewing process include maltingmillingmashinglauteringboilingfermentingconditioningfiltering, and packaging. There are three main fermentation methods, warmcooland spontaneous. Fermentation may take place in an open or closed fermenting vessel; a secondary fermentation may also occur in the cask or bottle. There are several additional brewing methods, such as barrel aging, double dropping, and Yorkshire Square.