Beer is the most popular drink in the world, after tea. It dates back to early Egyptian and Greek times and was most likely introduced into England by Roman armies. Brewing beer requires water, grain, hops and yeast.
     The process begins with grain -- usually barley -- which has been processed in a technique known as malting. In the malting process, barley is steeped in water to allow the grain to germinate, in order to activate enzymes and to convert the stored starches into the simple sugars necessary for fermentation. The germinated grain is called malt. The malt is removed from water, dried and roasted to varying degrees, much as coffee beans are. With few exceptions, breweries purchase their grain in this condition from malting houses that supply the brewing and other industries.
     The first step in brewing is the milling of the malt, to crack the hard barley husk and expose the sugars stored within. Milling is followed by mashing, which involves mixing the milled malt, now referred to as grist, with heated water in a brewing vessel known as the mash tun. Mashing converts more of the starches to sugar, and removes other solubles from the grist, forming a hot porridge-like mixture called mash.
The mash is next transferred to the adjacent lauter tun, where, in a process known as lautering, the sweet liquid is separated from the grain. The grain is removed as a waste product and often ends up as livestock feed for local farmers.
     The sweet liquid is known as wort (pronounced wurt), and is transferred to the brew kettle, where it is again boiled. At this point, the brewers add hops. Hops are the conical flower of the humulus lupulus vine, grown in several regions of the world. Where the malt contributes color, sweetness and body to the finished beer, the hops contribute flavors perceived as bitter, as well as floral or spicy aromas.
After boiling, the wort is transferred to another vessel known as the whirlpool, where centripetal force removes unwanted proteins, hop leaves and other particulate matter. The wort is rapidly cooled as it passes through a heat exchanger and is oxygenated. The wort is then sent directly to a fermenter where the yeast is pitched, or added.
     Fermentation, a process in which the singled-celled yeast convert sugars in the wort into carbon dioxide and alcohol, follows. Fermentation can last up to a week. Depending upon the strain of yeast employed (there are thousands of genetic varieties, or strains, used by brewers throughout the world) and upon how it is managed, yeast can greatly affect the flavors and aromas of the finished beer. This is most evident in the character of traditional styles such as Bavarian weiss bier or Belgian lambic.
     All beer is classified as either ale or lager, depending upon which of two types of yeast has been used in fermentation. Ales trace their heritage to the British and Belgian brewing traditions. Ale yeast ferments at relatively warm temperatures and at the top of the fermenting vessel. Lagers, which trace their heritage to German brewing culture, employ a yeast that works at cooler temperatures and at the bottom of the fermenting vessel.
A period of conditioning follows fermentation.
For lagers, this conditioning period takes place in a lager cellar, where the beer is stored at near-freezing temperatures for between four and 12 weeks, depending upon style. Ales also condition at near-freezing temperatures for one to two days. Whether it be lager or ale, the beer is then filtered to remove residual yeast and packaged in bottles or kegs. Some unique styles, such as traditional Bavarian weiss bier, are not filtered. The yeast remains in suspension giving it a cloudy opacity, rather than a sparkling brilliance.