Chemistry of Making Beer
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Making the Wort
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The main ingredients in modern beer are water, hops, barley and yeast. The first step in the brewing process is the malting of barley. The barley is allowed to germinate. This process creates enzymes that transform the starch contained within the seed into sugars. The grain then is crushed to separate the husks, mixed with water, dried into a "mash" and warmed to about 150 degrees Fahrenheit, which liquefies the barley starches into dextrin and then maltose, a sugar that will be fermented later in the process.
Lautering and Boiling
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At this point, enzymes in the grain are deactivated by another warming period, a process known as "mashout." The mash is then drained and the barley husks are lautered, or rinsed, with warm water. The result is a barley wort, the basic liquid material that will be fermented to create the finished beer. Proteins have been separated from the mash by boiling, which is necessary to achieve clarity and the ability of the beer to hold a "head." Hops are added to the wort boil to add the desired aroma and bitter flavoring. After boiling, the wort is cooled, which removes proteins and tannins. Cultivated yeast is then added to the mixture, in the process of "pitching."
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Fermentation
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The yeast then begins to reproduce, absorbing the oxygen from the wort to create new cells. When the oxygen supply is exhausted, the yeast begins to ferment, transforming molecules of glucose into ethyl alcohol and carbon dioxide, which is vented away. When the sugars are completely used up, fermentation of the yeast stops. Carbon dioxide is then injected into the beer to carbonate it.
A higher fermentation temperature creates ale, in which the fermenting yeast rises to the top of the vessel ("top fermented"). A lower fermentation creates lager, which is also known as "bottom-fermented." Lambic beers, which originated in Belgium, are made with wild yeast. Clarifying agents are added to the beer to precipitate the remaining proteins in the liquid and make it transparent.
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