Figure 1. Mesopotamian clay tablet. Source: Courtesy of the Beer Institute.

ers or lakes that froze in the winter. Ice was cut from these and stored in cellars for refrigeration during the summer. Thus New York, St. Louis, and Philadelphia became centers of lager brewing. By the 1870s mechanical refrigeration was invented and used first in a brewery in Brooklyn.

Lager beer has almost completely replaced ale as the beverage of choice, and today ale is only produced in the United Kingdom and parts of Canada, with only token amounts elsewhere. In the United Kingdom ale is referred to as beer and what the rest of the world calls beer is called lager. In what follows, beer will be used to refer to both ale and beer.

The Making of Beer

Beer production involves three distinct but interrelated stages. First is the preparation of an extract of the malt and the grains selected. This extract is called wort (pronounced to rhyme with "hurt"). This step takes place in the brewhouse and is often referred to as brewing. It takes about 4-10 h. A photograph of a typical brewhouse is shown in Figure 2.

The next stage is fermentation, the conversion of this liquid by yeast into beer. This is a temperature-controlled process that takes 3-10 d.

Fermentation is usually conducted in large stainless steel vessels that hold the volume of an entire brew, or several brews. Their size may be between 7,000 and

Figure 2. Brewhouse, showing lauter tubs above and kettles below. Source: Courtesy of Anheuser-Busch, Inc.

375,000 gal, and they may be horizontal rectangular in shape, or vertical cylindrical, with or without a conical bottom. The conical bottom allows simple gravity expulsion of yeast. A set of cylindroconical tanks are shown in Figure 3. The rectangular tanks require manual raking of yeast for reuse in subsequent brews.

The final stage is finishing or the refining of this liquid into salable beer by the brewery. It may take 2-25 d. It takes place in tanks equal in size to the fermentation tanks

Figure 3. Cylindroconical tanks. Source: Courtesy of Paul Mueller Company.

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