Microbrewing Science by Christopher L. Brown

Author:Christopher L. Brown [Brown, Christopher]
Language: eng
Format: epub
Publisher: Cognella Press
Published: 0101-01-01T00:00:00+00:00

YEAST SIGNATURES AND AVOIDANCE OF OFF-FLAVORS

While brewing beer, it is helpful to think of this as yeast cultivation, as opposed to a process of manufacturing beer. Providing the proper and fresh materials and conditions that are as nearly optimal as possible will keep your yeast culture healthy, and there is no better shortcut to a good batch of beer.

As your yeasts ferment sugar into alcohol, be aware that this is not necessarily a linear, one-way transitional pattern. In other words, some of the steps in the fermentation pathway can have branches or detours, leading to the production of other materials that may have undesirable effects on the way your beer tastes. It is also possible that some of the products of normal fermentation can be converted into other compounds with undesirable influences on the balance of flavors in a beer. This can be a result of the enzymes that are present in the yeast that you are using, oxidation or other kinds of chemical reactions, or “mass action effects.” These are chemical reactions that are driven by a buildup of precursor materials that pushes their reaction toward increased conversion into a product that might normally be less abundant. Similarly, some intermediate forms that would normally be converted into desirable or agreeable tasting compounds may build in concentration because they cannot be converted in the usual manner.

These are qualitative changes in the fermentation process that may be layered on top of the particular metabolic traits of the yeast that you are using. Some are related to the chemical or physical characteristics of the environment that they are in; unusual temperatures can promote particular chemical reactions, for example. It is also true that changes in the specific gravity of the wort or an unusual pH can also promote conversions that result in unwanted flavors. For the most part, such reactions result in tastes that are collectively called “off-flavors”—an assortment of tastes that most beer aficionados would prefer not to have in their beer. Each off-flavor has a specific biochemical origin, and the experienced brewer can studiously avoid generating them (Janson, 1996).

Yeasts that you buy from a brewing supply company are domesticated organisms that are selected for their ability to work under brewing conditions with a predictable and desirable outcome. That means that they will be healthy and prosperous alcohol-producers working in a fermenter, of course, but it typically also means that their fermentation products will include compounds that result in some pleasant balances among their flavors. It is also part of the bargain that objectionable flavors will be held to a minimum under routine conditions.

Each strain of yeast has its own characteristic balance of flavors, or its “yeast signature.” Choosing your yeast is partly a matter of selecting one with the right yeast signature for the sort of beer that you want to make, or one that is expected to produce the combination and concentrations of tastes and aromas that appeal to you. Some are workhorses—straightforward producers of ethanol and a moderate assortment of tastes that will make you a clean-tasting beer.

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