Beer is the world’s oldest and most popular alcoholic beverage. Some of the earliest known writing refers to the production and distribution of beer. It is produced by the fermentation of sugars derived from starch-based material — the most common being malted barley; however, wheat, corn, and rice are also widely used, usually in conjunction with barley.
The starch source is steeped in water. Enzymes in the malt break down the starch molecules, producing a sugary liquid known as wort, which is then flavoured with hops, which acts as a natural preservative. Other ingredients such as herbs or fruit may be added. Yeast is then used to cause fermentation, which produces alcohol and other waste products from anaerobic respiration of the yeast as it consumes the sugars. The process of beer production is called brewing.
Beer uses many varying ingredients, production methods and traditions. The type of yeast and production method may be used to classify beer as ale, lager or spontaneously fermented beer. Some beer writers and organizations differentiate and categorize beers by various factors into beer styles. Alcoholic beverages fermented from non-starch sources such as grape juice (wine) or honey (mead), as well as distilled beverages, are not classified as beer.