Beer is the world's oldest and most popular alcoholic beverage, selling more than 133 billion litres (35 billion gallons) a year. It is produced through the fermentation of starch-based material, commonly barley, though cassava root in Africa, potato in Brazil, and agave in Mexico, among other starch sources, have been used.
Only beverages produced by this method are considered to be beer. Neither alcoholic beverages made from the fermentation of sugars derived from non-starch sources (e.g., grape juice or honey), nor beverages which are distilled after fermentation should be classified as such.