Beer-making, Biology of
Beer is made by fermentation of grains, principally barley ( Hordeum vulgare ). Other grains, including wheat and rice, may be added to develop particular flavors. The grain is first allowed to germinate by soaking it in water. As part of its germination process, the grain produces amylase enzymes that break down the starches of the endosperm (part of the seed) into sugars. At a certain point, germination is halted by rapidly drying the grain, in a process called kilning, to produce "malt." More prolonged kilning produces a darker beer. The malt is then ground and mixed with more water to reactivate the amylases and complete the liberation of the sugars.
The resin-filled flowers of the hops plant ( Humulus lupulus, Cannabinaceae family), are added for aroma and bitter flavor, and the mixture is boiled to bring out the flavor. Boiling also kills unwanted microorganisms that might spoil the fermentation that follows. Yeast is then added to ferment the sugars to ethyl alcohol. Ales are made at room temperature using the yeast Saccharomyces cerevisiae, whereas lagers use Saccharomyces uvarum at cooler temperatures. The final alcohol concentration of most beers is about 5 percent. Some beers are naturally carbonated by bottling before fermentation is complete, but most commercial beers require addition of carbon dioxide after fermentation.
Beer is probably the oldest of alcoholic beverages and has been made for thousands of years, at least as far back as classical Egyptian civilization of five thousand years ago. Modern beer styles originated in Germany, the Czech Republic, and the United Kingdom, which still claim production of some of the finest beers in the world.
Jackson, Michael. The New World Guide to Beer. Philadelphia, PA: Running Press, 1997.