Brewing beer is a complex process that involves breaking down the starches in grains into a sugary liquid, called must, and fermenting the sugars in the must into alcohol and carbon dioxide using yeasts. This process is known as brewing and it results in beer production. Most often, malted barley is used, but wheat, corn, rice and oats can also be used. As the starch sugars in the wort ferment, ethanol is produced and the beer is carbonated.
To start the fermentation process, the cooled wort is transferred to a fermentation vessel to which the yeast has already been added. If the beer being made is an ale, the wort will be kept at a constant temperature of 68°F (20°C) for about two weeks. If it's a lager beer, the temperature will be maintained at 48°F (9°C) for about six weeks. As fermentation produces a substantial amount of heat, the tanks must be constantly cooled to maintain the proper temperature. The product of glycolysis is two three-carbon sugars, called pyruvates, and some ATP (adenosine triphosphate), which supplies energy to the yeast and allows it to multiply.
With craft beers becoming increasingly popular in recent years, it's important to know, study and characterize them in terms of their raw materials and chemical composition. Beer is derived from malted cereals and grains, usually barley and wheat, and less commonly from sorghum, starchy vegetables and rye, along with water, hops and a strain of yeast. As a result of high temperatures used in the production of dark malts, Maillard reaction products (MRP) are synthesized which give beer its sensory profile. In addition, since most esters are present in concentrations that vary in the threshold value, minor variations in their concentration can have critical effects on the organoleptic properties of beer. Diacetyl (2,3-butanedione) is an important volatile compound that affects beer quality. Biocomposites derived from humulones, cinnamic and benzoic acids, prenyl chalcones, procyanidins and catechins have also been reported to be directly related to the high antioxidant capacity of beer. When overgrowth of fungi occurs in pre-harvest of grain or during storage, dangerous levels are introduced into the beer process flow.
In large industries, beers are filtered and pasteurized to remove yeast and stabilize the beer before packaging. Phenolic compounds such as hydroxycinnamic acids (p-coumaric acid and isoferulic acid) and flavan-3-ols (catechins and epicatechins) in malt and beer have a strong impact on the antioxidant activity (increased shelf life) and colloidal stability (foam and haze) of beer. Brettanomyces yeasts (Teleomorph Dekkera), including Brettanomyces bruxellensis, Brettanomyces custersii and Brettanomyces anomalus are harmful contaminants of most beers and other alcoholic beverages. However, their presence is often encouraged in other types of beer.