Beer Fact Friday: Fermentation

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Brewing Process - Fermentation

For the past few weeks, we’ve been going over the brewing process and explaining each of its stages in-depth. Those stages: Milling, Mashing, Lautering, Boiling, Whirlpooling, and Cooling. (Swing back through past Friday posts for a refresher.) During all of these steps, the liquid we’ve been working with is loaded with sugar but contains no alcohol, and is known as “wort.” In the fermentation stage, our wort finally becomes beer. 

Wort is fun to occasionally taste, but it’s not a beverage you want more than a few sips of. For one thing, it’s very sweet. All of the sugars that we extracted from the malt during the Mashing stage are still contained in the liquid, making it thick and cloyingly sweet. Also, wort doesn’t contain any alcohol—and if there’s no alcohol, then what’s this all been about? So in order to make our wort potable and enjoyable, we need to chemically change all that sweet stuff into alcohol and other compounds. 

We do that by adding yeast, microscopic organisms (technically fungi) that can convert sugar into alcohol. Once the yeast is “pitched”—AKA added to the wort—it reproduces, dividing itself until billions of cells saturate the liquid. Then it gets to work. The yeast cells consume malt sugars, converting them into alcohol and carbon dioxide. Some yeast types will also excrete large amounts of aromatic compounds called esters and phenols, which can imbue a beer with flavors such as apple, banana, pineapple, pear, and cloves.  

Fermentation tanks at our production brewery
Fermentation tanks at our production brewery in Tempe.

Fermentation can take place inside any number of vessels. Most homebrewers use simple glass jugs that work just fine for their purposes; commercial brewers usually employ unitanks. Even if you might not recognize that name, you know what we’re talking about: They’re the large cylindrical tanks with slanted, cone-shaped bottoms you find in the back of almost any modern brewery. That cone at the bottom of the tank is designed to collect yeast that have sunk after they’ve finished fermenting the beer; these yeast can actually be reused in subsequent batches of beer.

Depending on the type of yeast used, the fermentation process can take anywhere from a few days to several months. Ales (like, say, Kilt Lifter) will usually finish fermenting in two weeks; lagers (our own Golden Lager, for instance) tend to take a month minimum. 

Once fermentation is complete, it’s time to filter. We’ll cover that step next Friday.

Beer Fact Friday is our weekly exploration of the topics that make beer the world’s most interesting beverage. Check back here next week—or follow us on FacebookInstagram, or Twitter—for more fascinating beer trivia. 

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