Beer is an alcoholic drink made from sugars derived from grain (usually barley). Hops are usually added to beer to give the beer a bitter taste.
Harvested grain has no sugar and is not fermentable in its raw state. To produce sugars the grain is first germinated and dried (called "malting"). It is then steeped in warm water. The warmth activates enzymes in the malt which turn the grain's starch into sugars. The sugars produced are strained from the residual grain and boiled with hops. Yeast is added to the resultant liquid (called "wort"). It is the yeast which ferments the sugars producing alcohol.
Beer most frequently has from 3 to 7 percent alcohol by volume, although both lower and higher alcohol versions exist, with the strongest versions exceeding 20%. It is therefore important, in order to practice moderation in drinking, to know the alcoholic strength of the beer one is consuming. In the United States, this can be difficult, as federal laws prohibit beer companies from advertising their products on the basis of strength, and many companies avoid listing strength on the can or bottle at all, in order to minimize the risk of being targeted for prosecution.