Brewing is to product by steeping a starch source (commonly cereal grains, the most popular of which is barley) in water and fermenting the resulting sweet liquid with yeast. It may be done in a brewery by a professional brewer, at home by homebrewer, or by a variety of traditional methods such as communally by the indigenous people in Brazil when making cauim. 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. Less widely used starch sources include millet, sorghum and cassava. Secondary source, such as maize, rice, or sugar, may also be used, sometimes to reduce cost, or to add a feature, such as adding wheat to aid in retaining the foamy head of the grain bill. Steps in the brewing process include malting, milling, mashing, lautering, boiling, fermenting, conditioning, filtering and packaging. There are three main fermenting methods, warm, cool and spontaneous. Fermentation will 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.