The Role of Yeast in Home Brewing

The driving factor behind fermentation and the very existence of beer itself is due to yeast. You owe every beer ever enjoyed to the asexual reproduction of a fungus.

But this isn’t just any old fungus, we’re talking Saccharomyces cerevisiae, a very particular type and not to be confused with mushrooms, baking bread, or causing infections. The main idea here is that yeast does not require oxygen to exist but instead metabolizes simple sugars in a process known as fermentation and reproduces itself by “budding” off daughter cells.

The two main types of brewer’s yeast are “ale yeast” and “lager yeast”, which ferment under different conditions and have a large impact on the eventual taste of your home brew. Ale yeast is conveniently named because of the types of home brew you can expect using this strain. This yeast ferments best at warmer temperatures (68-73 F) while Lager yeast instead prefers cooler temperatures and requires more time. We experienced the importance of temperature first hand when our English Brown Ale fermented in colder temperatures than ale yeast requires. The result was low ABV and an off-tasting beer.

Yeast is introduced to your finished (and cooled) wort by pitching it, which really is just a fancy term for “stir up the wort real good and add the yeast.” Yeast can be added dry from the package, as the directions usually indicate, though the proper method is to rehydrate in a solution of boiled water. This “wakes up” the yeast and gets it ready for the feeding frenzy. Just for a bit of scope, we’re talking billions of yeast cells here. Once they have a few weeks to feed and multiply, that number can almost double.

So, the more important question you’re asking is: How does this fungus give me a buzz when I drink beer? Let’s imagine our bucket of boiled wort sitting in the basement with billions of yeast cells recently pitched. The yeast are pretty happy with the temperature, they’re darn hungry, and they start feasting on the simple sugars (glucose + maltose) in our bucket and release carbon dioxide and ethyl alcohol as waste products. Other chemicals are released as well depending on the conditions but CO2 and alcohol are a definite. You can later measure the amount of alcohol with close precision using a hydrometer, which compares liquid density before and after fermentation.

So, all of this really boils down to a fungus eating a great meal and passing gas.