Brewing is the production of beer by steeping a starch source (commonly cereal grains, the most popular of which is barley) in water and the resulting sweet liquid with yeast. It may be done in a brewery by a commercial brewer, at home by a homebrewer, or communally. Brewing has taken place since around the 6th millennium BC, and archaeological evidence suggests that emerging civilizations, including ancient Egypt and Mesopotamia, brewed beer. Since the nineteenth century the has been part of most western economies.