Beer
Beer has been a staple of African, Mediterranean and European diets since ancient times. It was likely discovered in ancient Egypt or Mesopotamia and predates written history. In its simplest form, beer is a cloudy alcoholic beverage made (or "brewed") from fermented grain. Most medieval and modern beer includes malt made from hops to clarify the beer and make it tangy and foamy, although some brands of wheat beer can give an authentic ancient beer-drinking experience, especially when consumed warm.
Beer in Period
Beer was a staple drink for all social classes. It was cheap, easy to make, and far, far safer than water, since the mild alcoholic content killed the bacteria and parasites common in the medieval drinking supply. Period beer was about four- or five-percent alcohol by volume, at a minimum, although a much milder form known as small beer was also commonly consumed. Small beer has an alcoholic content of only one- or two-percent, and was a staple beverage for children, the infirm, and the elderly. To closely mimic a medival beer-drinking experience, go for a dark and flavourful European beer, served at a few degrees below the ambient room temperature.
Modern Beer
The alcoholic content of modern beer varies greatly depending on where it is made: Belgian beer, for example, is regularly seven- or eight-percent alcohol, while American beer, at three- or four-percent, is often derided as being a little like making love in a canoe, as the Canadian saying goes. In addition, European and Australian beers tend to be more flavourful than their North American equivalents.
Hops are the ubiquitous flavouring, bittering and preserving agent in modern beer. While hops have been used in some beers since antiquity, cultivation of hops for brewing is generally considered to have become widespread in the 13th_century. Various bittering herbs and plants were used previously for similar results. (See also: Wikipedia's entry on beer.)
The Liquor Control Board of Ontario (LCBO) in Canada defines a single drink of beer as eight fluid ounces at the standard Canadian strength of five- to six-percent alcohol.
Alcohol contents of modern beer are often driven by excise taxes, rather than traditional style considerations. For example, Victoria Bitter ("VB"), was recently reduced from 4.9% to 4.8% alcohol content to save the brewer around A$20 million per year in excise taxes.