Beer is an alcoholic beverage made from malted grains, hops, yeast, and water. The grain is usually barley or wheat; however, corn and rice are sometimes used as well. Fruit, herbs, and spices may also be used for special savour. In the distant past, the terms "beer" and "ale" meant different things. "Ale" was originally made without using hops, whereas "beer" was made using hops. Since virtually all commercial products now use hops, the term "beer" encompasses two broad categories: ales and lagers.

Source : FAQ of alt.drinks.beer