Microbrewing Science by Christopher Brown

Author:Christopher Brown [Brown, Christopher]
Language: eng
Format: epub
Publisher: Cognella, Inc.
Published: 2012-10-02T21:00:00+00:00

The Biochemistry of Beer

The whole idea of beer is the transformation of an aqueous solution by way of the fermentation of sugars into a mild ethanolic solution, with an agreeable set of flavors, colors, aromas, and dissolved gases that establish a particular style and tone of beverage. Some of the flavor determinants are obvious; beer is an aqueous solution with a balance of sweetness and bitterness that is defined by the presence of dissolved sugars and hop acids. Bitterness is determined by the amounts of a series of derivatives of hop alpha acids or iso-alpha acids and by their proportions relative to each other. Color is defined nearly completely by the barley used for mashing and particularly by the amounts used and the darkness that has been imparted to them by kilning. Other compounds have subtler influences on the balance of tastes and aromas in beer, including a variety esters and sulfides that are byproducts of yeast metabolism of sugars.

The choice of hops varieties, the amounts used, and the timing of hops additions determine the hop flavors that ultimately wind up in a beer. The alpha acids consist of a family of similarly structured compounds called the humulones. Of these, humulone is considered the most desirable of the three primary components, while cohumulone is more abundant but it is associated with less refined or “harsh” bitter tastes. A third form contributing alpha acid flavor and aroma is adhumulone. The ratio of humulones (H) to cohumulones (C) is considered to be a worthwhile indicator of hop quality, and sometimes hops are described by providers in terms of their H/C ratios. Indeed several of the classic and most desirable European noble hops have high H/C ratios. Boiling results in the conversion of humulones to their respective isomers in cis- and trans- forms, and these iso-alpha acids are among the desired end products of hop extraction that remain in the finished beer, and which produce the preferred bittering effect. Note that cohumulnes have higher water solubility than humulones, so short boils produce worts with relatively reduced H/C concentrations.

Alcohols contribute more to beer than just the famous psychological effects, euphemized by fraternity participants as “beer buzz”, a “kick”, “beer goggles”, and so on. Moderate alcohol consumption has been correlated repeatedly with positive cardiovascular effects as well as enhanced survival and longevity prospects (reviewed by Bamforth, 2003). Lower, higher, or excessive rates of consumption can reverse or eliminate these health effects. The yin/yang nature of the effects of β–glucans has already been mentioned; these polysaccharides are present in varying degrees in beer and are generally considered undesirable by beermakers despite their positive effects on human health.

Alcohol is also believed to influence the quality of beer through several other means; fermentation produces not only ethanol but a variety of fusel alcohols or “higher alcohols”. These produce different flavors directly and indirectly. Fusel alcohols impart solvent or alcoholic tastes and also are involved in the production of esters. Variable amounts of the fusel alcohols are accumulated under

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