Beer

I

Introduction

Beer, alcoholic beverage made from cereal grains, usually barley, but also corn, rice, wheat, and oats. Beer is made using a process called fermentation, in which microscopic fungi called yeast consume sugars in the grain, converting them to alcohol and carbon dioxide gas. This chemical process typically produces beer with an alcohol content of 2 to 6 percent. Over 70 styles of beer are available today. Each style derives its unique characteristics from its ingredients and subtle differences in its brewing process.

Throughout history, wherever cereal grains were grown, humans made a beerlike beverage from them: they used wheat in Mesopotamia, barley in Egypt, millet and sorghum in other parts of Africa, rice in Asia, and corn in the Americas. Today, beer making is a major industry worldwide. In 2002 in the United States, 1,800 brewers produced almost 175 million barrels of beer, and on average, each American consumed nearly 83 liters (22 gallons) of beer.

II

Beer Ingredients

Four basic ingredients are used to brew beer: grain, hops, yeast, and water. Grain contains the natural sugars required for fermentation. It also provides beer with flavor, color, body, and texture. Hops are small, green, cone-shaped flowers from the hop plant, a vine related to the nettle plant. Over 50 varieties of hops are grown throughout the world, mostly in Europe, Australia, and North America. Hops provide beer with a spicy, bitter flavor and contribute natural substances that prevent bacteria from spoiling beer. Two species of yeast used to make beer, called brewer’s yeast, are Saccharomyces cerevisiae and Saccharomyces uvarum. Each yeast species is used in a slightly different method of fermentation and produces a distinct type of beer.

Water constitutes as much as 95 percent of the ingredients used in the brewing process. The mineral content in water—in particular, the levels of salts such as calcium, sulfate, and chloride dissolved in the water—influences the quality and flavor of the beer it is used to produce. Modern brewers add minerals and other natural elements to water or eliminate them by boiling or filtration so that the water used in the brewing process always produces beer with the same flavors. This enables brewers to produce identical-tasting beer at different brewing locations throughout the world.

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III

The Brewing Process

The first step in brewing, called malting, involves steeping the grain in water for several days until it begins to germinate, or sprout. During germination, enzymes within the grain convert the hard, starchy interior of the grain to a type of sugar called maltose. At this point, the grain is called malt. After several days, when the majority of the starch has been converted to sugar, the malt is heated and dried. This process, called kilning, stops the malt from germinating any further. A portion of the malt may be further roasted to varying depths of color and flavor to create different styles of beer.

After kilning, the dried malt is processed in a mill, which cracks the husks (the outer coating of the grain). The cracked malt is transferred to a container called a mash tun, and hot water is added. The malt steeps in the liquid, usually for one to two hours. This process, called mashing, breaks down the complex sugars in the grain and releases them in the water, producing a sweet liquid called wort. The temperature and amount of time used to mash the malt affects the body and flavor of the finished beer.

In the next step, called brewing, the wort is transferred to a large brew kettle and boiled for up to two hours. Boiling effectively sterilizes the wort to kill any bacteria that may spoil the wort during fermentation. During this stage of the brewing process, hops are added to the wort to provide a spicy flavor and bitterness that balances the sweetness of the wort. The types of hops used and the length of time they are boiled are determined by the style of beer being made. To produce a beer with a stronger, more bitter flavor, hops are boiled for at least 30 minutes and often longer. This enables the bitter oils in the hops to fully infuse into the wort.

Other ingredients may also be used to influence the flavor of the finished beer. For example, brewers of pale and light-bodied beers often add other cereal grains, such as corn and rice, to achieve the desired lightness in their product. Many large American breweries add corn and rice that has first been cooked to a gel-like consistency. This gives the beer a lighter color and body and a more mellow taste than beers produced from barley alone.

After brewing, the wort is cooled and then strained to remove the hop leaves and other residue. The brewer transfers the wort to a container in which it can ferment. This vessel may be a deep, flat container with an open top or a tall cylindrical vat with a conical base. Yeast is then added or pitched into the wort to begin fermentation. Saccharomyces cerevisiae floats on top of the liquid as it ferments the grain sugars and prefers warm temperatures ranging from 16° to 22° C (60° to 72° F). Saccharomyces uvarum sinks to the bottom of the liquid and ferments best at cool temperatures ranging from 3° to 10° C (38° to 50° F). The first fermentation lasts from a few days to two weeks. When the yeast has consumed most of the fermentable sugar, the wort becomes beer.

The beer is transferred to an airtight container, called a conditioning tank, for a second fermentation or aging period, where the beer becomes naturally carbonated. Some brewers inject carbon dioxide gas into the beer when aging is complete to give it a bubbly, effervescent quality. Aging lasts for a few weeks to several months, depending on the type of beer being produced.

After aging, the beer may appear somewhat cloudy from yeast cells and other particles that remain suspended in the liquid. The most common method of removing these impurities is filtration, a process in which the finished beer is pumped, under pressure, through a sterile filtering system that traps nearly all of the suspended particles from the liquid, resulting in a clear liquid. Even after filtration, however, some yeast may remain in the beer. To kill the remaining yeast, the beer is pasteurized, or heated to 82° C (180° F) after it has been sealed in cans or bottles. Draught beer, which is stored in metal kegs, usually is not pasteurized and must be kept refrigerated to prevent it from spoiling. Some brewers and beer drinkers believe that filtering and pasteurizing beer robs it of much of its original flavor and character.

IV

Beer Characteristics

The two major categories of beer are ales and lagers, and the yeast used in fermentation determines the differences between the two. Ales are fermented with Saccharomyces cerevisiae at warm temperatures for short periods of time, typically a week. This yeast ferments in warmer temperatures to produce a fruity flavor that characterizes ale. Ales are aged, or conditioned, for one to three weeks. Ales should be served at room or cellar temperature—about 13° C (about 55° F).

Lagers are usually drier, crisper, and less fruity in taste than ales. Lagers are fermented with Saccharomyces uvarum at cooler temperatures for longer periods up to two weeks, which encourages the flavor components in lagers to combine and mellow. Lagers are aged for up to 12 weeks. Lagers are best served chilled.

All beer can be further described by three additional variables: color, bitterness, and gravity. Color is determined by the type and amount of malt used to make the beer. For example, lightly roasted malt produces a light-colored beer, while beer made only with barley that has been dark roasted is nearly black in color.

Bitterness depends on the type and amount of grain and hops used in the beer's production. Beers made with wheat, for example, are generally less bitter than beers made with dark-roasted barley. Bittering hops, such as those grown in the Pacific Northwest of the United States, are used to make beers with a more bitter flavor. The mineral content of the brewing water can also accentuate hop bitterness. Beer made with water that has a high level of dissolved minerals is more bitter than beer made with water low in minerals.

Gravity refers to the beer’s density, or the amount of dissolved sugars in the wort. As more sugars dissolve in the brewing water during mashing, the density of the wort increases. The yeast consumes these sugars to produce alcohol during fermentation, so elevated sugar levels translate into a higher alcohol content in the finished beer.

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