Brewing 101: Yeast

What is Yeast?

Yeast is the workhorse of the brewery. There’s a saying, “(Wo)man makes wort, yeast makes beer.” As mentioned above, yeast takes sugars extracted from the malt and turns those sugars into alcohol and carbon dioxide, CO2.

Yeast also modifies other compounds extracted from the grains and creates exciting flavor and aroma compounds.

Types of Yeast Used in Brewing

Two main types of yeast are used in brewing beer: “ale” yeast and “lager” yeast.

Ale to the Yeast

“Ale” yeast belongs to the species Saccharomyces cerevisiae and typically works well in fermentations at “room” temperature, 18–24°C/65–75 °F.

Ale yeast produces a wide spectrum of flavors, from clean and neutral (American Chico-type or German ale strains), to banana and spice (German hefeweizen/Belgian wit strains), and berries and stone fruit (English strains).

A lot of these flavors are present due to chemical compounds called esters (fruity) and phenols (spice).

Lager than Life

“Lager” yeast belongs to the species Saccharomyces pastorianus, a hybrid yeast derived from Sacchormyces cerivisae and Sacchormyces eubayanus, a cold-tolerant yeast.

Beer made with strains of Saccharomyces pastorianus is typically fermented cool, around 10–15 °C. After fermentation is complete, lagers are typically stored cold to condition. The term “lager” is from the German word “lagern” for “to store”.

With a cooler fermentation, lager yeast produces fewer ester compounds than ale yeasts.

Unlike their ale yeast cousins, lager yeast is able to ferment a broader range of sugars, such as melibiose. Since they can ferment more of the types of sugars present in the wort, lager yeast typically have higher attenuation rates and produce “crisper” tasting beer.

Wild Bonus

Another genus of yeast present in brewing is Brettanomyces, or “Brett”. The description of some of the flavors produced by Brett are not, well, appetizing, but they can contribute to a wonderfully complex profile.

  • Band-aids, barnyard
  • Smoke, spice, cloves
  • Wet horse blanket, cheese

Those might not sound like the tastiest of flavors, but the concentration, or how much of it is in the beer, can make a world of difference.

Care for Your Yeast and They Will Bring You Great Things

Treat your yeast right and they will produce a delicious beer in return. A critical aspect of treating your yeast right is temperatures during fermentation. We’ve illustrated this by using cupcakes as an example. Using the wrong temperature or letting things get out of hand can lead to unexpected, and sometimes undesirable, results.

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