Beer has but four ingredients:
BARLEY
Any grain can be used to make beer. There are popular wheat beers, such as Blue Moon, as well as oat beers, but barley is most commonly used. Barley is a cereal grain not particularly good for making flour or bread but excellent for making beer.
Barley cannot be used as is but must first be “malted.” In this process, it is moistened and allowed to sprout roots (germinate) so seeds become rich in the starch they need as a food for growth. The barley is then heated to a temperature that stops growth but allows diastase, a natural enzyme, to remain active and convert the starch to sugar.
Some of the malted barley may be heated at a higher temperature to roast it. Roasted malt can no longer turn starch into sugar but is often used to affect the color and flavor of the beer.
Types of barley are distinguished by growth of two, four, or six rows of seeds along the stem at the top of the stalk. European brewers prefer two-row barley because it malts best and has higher starch to husk ratio than the others. American brewers prefer six-row barley because it is cheaper to grow and has a higher concentration of enzymes needed to convert starch in the grain into sugar.
WATER
Beer is more than 90% water. The mineral content of local water was once a strategic part of the taste of a region’s beers (Olympia: “It’s the Water”) but today, almost any water can be chemically adjusted to create the style of beer desired.
HOPS
Hops are flowering vines whose flowers are dried and used as a preservative and for their essential oils. Bittering hops add flavor to balance the sweetness of the beer. Aroma hops are added to affect the beer’s fragrance. There are more than 50 varieties of hops and each has its own distinct flavor and aroma profile.
YEAST
Yeast is a micro-organism that feeds on sugars in the malted grain and converts them to alcohol and carbon dioxide. This fermentation process can continue until alcohol content reaches 14-18%, at which point the solution becomes toxic to the yeast and it dies. Yeast does not ferment all sugars, thus it leaves the malted grain with a sweet taste at the end of fermentation.
Some yeast strains add little to a beer’s flavor. Others produce phenols giving a spicy or clove-like taste, esters which add a fruity taste, or diacetyls which produce a butterscotch or woody taste. The strain of yeast used depends on the style of beer being brewed.
Flavorings are not an essential ingredient but are often added to give beer a unique taste. These number in the hundreds and range from herbs such as rose hips and coriander, to spices such as cardamom seed and cinnamon sticks, to fruits such as strawberry and black currant.
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“I am a firm believer in the people. If given the truth, they can be depended upon to meet any national crisis. The great point is to bring them the real facts, and beer.” — Abraham Lincoln
“You can’t be a real country unless you have a beer and an airline. It helps if you have some kind of football team, or some nuclear weapons, but at the very least you need a beer.” — Frank Zappa
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The Ingredients of Beer website used as reference.