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So Yeah, Dood #11: Number of the Yeast

(Editor’s note: this is the latest in an ongoing series relating to the process of making beer, something near and dear to the hearts of many sports fans. For earlier installments please browse the category archives.)

Immediately following the end of the boil, brewers turn their minds to fermentation, the part of the brewing process that requires the least actual work but the most patience. Despite the seeming simplicity of this phase, careful choices must be made.

Yeast performs most of the legwork of brewing. By “digesting” sugars suspended in the wort, yeast respirates carbon dioxide just like we do, but it also produces another waste product: Alcohol. Given, there are certain sugars that the yeast can’t digest, and these unconvertible sugars give beer sweetness and aid in head retention.

Wort is cooled to below 80 degrees. A specific gravity reading is taken using a hydrometer. This determines the relative density of the liquid, and allows brewers to determine both when the beer has stopped fermenting, and what the beer’s final alcohol content by volume (ABV) will be. After aerating or oxygenating the wort, we pitch yeast.

Most of the time brewers decide on a particular strain of yeast that they want to use in advance of even starting their brew. They consider whether they want to produce ale or lager. Using yeast that rests on top of the wort (top-fermenting), and converts sugar to alcohol most efficiently at temperatures in the upper 50s, an ale is produced. Exactly the opposite, bottom-fermenting, cold temperature yeast (below 50 degrees) produces a lager.

Ale yeasts produce abundant flavors just by converting sugars. They give off chemical aroma and flavor compounds that affect the final taste of the beer. The higher the temperature, the more and different chemical flavors the yeast will produce.

Lagers ferment cold and produce fewer esters but also produce a much clearer final product. Most store-bought canned beer is lager. Brewers must maintain strict temperature control when using lager yeasts to avoid producing off flavors.

Of course, there are many different strains of yeast in both categories. California Ale yeast has a high alcohol tolerance, so it is more likely to continue to ferment when living in high concentrations of its own waste product. There are about as many types of yeast as there are styles of beer. Ale yeasts specifically cultured for use in wheat beers produce fruity, clove and banana-like esters. They give hefeweizens their characteristic cloudiness and fruity, citric flavor. Hefeweizen literally means beer with yeast, as the yeast is not intentionally cleared from the beer.

Coming next, from flat to fizzy: conditioning beer.

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