Brew Chem 101: The Basics of Homebrewing Chemistry
by Lee W. Janson Ph.D.

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Book Reviews of Brew Chem 101: The Basics of Homebrewing Chemistry

Book Review: Excellent introduction
Summary: 5 Stars

Although brewing chemistry is quite complex if one considers all the details, the basic idea is quite simple. Yeast ferment a sugar-rich combination of malted barley (or other grains, such as rye or wheat) and hops to produce alcohol and a variety of other metabolites that give the different flavors and qualities to beer. For example, I learned that one difference between lager and ale yeasts, besides the well-known distinction that ale yeasts are warm temperature, bottom-fermenting and lager yeasts are cold temperature, top-fermenting, is their ability to digest the sugar raffinose. Unlike sucrose or glucose, which are disaccharides and monosaccharides, respectively, raffinose is a heavier trisaccharide and ale yeasts are unable to metabolize it. Thus, heavier sugars, such as amylose, amylopectin, and so on, get into the final brew, which is why ales are typically heavier, fruitier, and sweeter than the cleaner and dryer-tasting lagers. The yeast primarily digests glucose, fructose, and sucrose, and maltose. Melibiose, a disaccharide like sucrose or maltose, is also present but can't be used. This is because the bond between the two glucose molecules is the same as raffinose.

The other important ingredient is hops. Hops are just the leaves of the hop plant, and the important thing is that the leaves contain glands that house essential oils and acids that provide bittering and flavoring to the finished brew. Although these glands contain 250 essential oils, the most important ones are the alpha acids such as humulone, cohumulone, and adhumulone, which are derived from the soft resins in the glands. The beta acids derived from the hard resins are less desirable. It is the isomerization of the desirable alpha acids, the changing of the molecule to a slightly different structural configuration with the same chemical constitution, that produces the pleasant bitterness in beer. The beta acids produce a less pleasant and desirable bitter quality.

Terpene molecules such as myrcene and humulene are also important. The oxygenation of humulene gives an elegant and refined flavor and aroma to beer. The same thing happens with myrcene, which produces a floral and herbal character from the production of two molecules, geraniol and linolool, and two other related molecules, geranyl acetate and geranyl isobutrate. However, this is also accompanied by a bitter quality that can be unpleasant if these myrcene by-products are present in too great a quantity, which is usually only a problem with certain species of hops, such as the Cascade strain, which contain high percentages of myrcene. But the widely used Cascade strain is prized for the floral and spicey ales they can produce.

There is also a discussion of ions and their contribution to flavor. For example, the English Burton ales are famous and use water from Burton on Trent which is high in calcium, sulfates, magnesium, sodium, and chloride. Janson notes that the presence of these molecules (and in the hands of competent brew-masters) results in a very complex and delicious brew, which is why one must pay attention to the quality of the water for certain styles of beer.

Well, I've gotten more nerdy in this review myself than I intended. But Janson's book will provide you with much more information if you're interested. Overall, a very readable and informative introduction to the area of brewing chemistry. After reading this, if you're game, pick up Dr. George Fix's Principles of Brewing Science, which is more technical, but which bridges the gap between the even more technical journals and big professional manuals of brewing chemistry. If you can get through that you're definitely eligible for your brewing chemistry nerd badge.

Summary of Brew Chem 101: The Basics of Homebrewing Chemistry

Here?s a class they didn?t offer at your school (although maybe you did some independent study of the subject). Here, in nontechnical language, is the real story of what?s going on in that bucket, carboy, and bottle. Does every brewer need to understand the chemistry involved in making beer? No. Will understanding it help every brewer make tastier beer? Absolutely.

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