Beer is the world’s most widely consumed and probably the oldest alcoholic beverage; it is the third most popular drink overall, after water and tea. The production of beer is called brewing, which involves the fermentation of starches, mainly derived from cereal grains—most commonly malted barley, although wheat, maize (corn), and rice are widely used. Most beer is flavored with hops, which add bitterness and act as a natural preservative, though other flavorings such as herbs or fruit may occasionally be included. The fermentation process causes a natural carbonation effect, although this is often removed during processing, and replaced with forced carbonation.
Beer is sold in bottles and cans; it may also be available on draught, particularly in pubs and bars. The brewing industry is a global business, consisting of several dominant multinational companies and many thousands of smaller producers ranging from brewpubs to regional breweries. The strength of beer is usually around 4% to 6% alcohol by volume (abv), although it may vary between 0.5% and 20%, with some breweries creating examples of 40% abv and above. Beer forms part of the culture of beer-drinking nations and is associated with social traditions such as beer festivals, as well as a rich pub culture involving activities like pub crawling, and pub games such as bar billiards. A microbrewery, or craft brewery, produces a limited amount of beer. The maximum amount of beer a brewery can produce and still be classed as a microbrewery varies by region and by authority.
There are many types of beer brewed, Ale, Pale ale, Stout, Lager, Wheat, Lambic etc. Beer is measured and assessed by bitterness, by strength and by color. The perceived bitterness is measured by the International Bitterness Units scale (IBU). Beer color is determined by the malt. Draught beer from a pressurised keg is the most common method of dispensing in bars around the world. A metal keg is pressurised with carbon dioxide (CO2) gas which drives the beer to the dispensing tap or faucet. Some beers may be served with a nitrogen/carbon dioxide mixture. Nitrogen produces fine bubbles, resulting in a dense head and a creamy mouthfeel. Some types of beer can also be found in smaller, disposable kegs called beer balls.