Beer has long played a role in human civilizations. Some social archaeologists even believe beer was a primary driver in the switch from hunter-gatherer to agricultural society. But where does yeast come from and how does it work? We’ll tackle this and more, below.

Who Discovered Yeast?

It took a long time for us humans to realize what was helping us make our alcohol. For many eons, beer was thought to “spontaneously generate.” For many, it was considered a blessing from the gods. And, in truth, it was.

Even the pioneering Bavarian brewers overlooked yeast when, in 1516, they wrote down their strict set of laws called the Reinheitsgebot that declared that beer should only be made of water, barley, malt, and hops. Since no one could yet see them, yeast functioned like magic.

It wasn’t until the mid-nineteenth century that Louis Pasteur identified the divine force that converted wort into beer as a microorganism. Pasteur’s “discovery” of yeast had a lasting impact on brewing practices and beer flavor, and led brewers toward using pure strains of yeast to obtain repeatable flavor profiles.

There are more than 1500 species of yeast. The type of yeast most commonly used to make beer is a single-cell organism called Saccharomyces Cerevisiae, which is technically classified as a fungus. And there are in fact thousands upon thousands of Saccharomyces Cerevisiae that have been cataloged and maintained by researchers and manufacturers such as White Labs and Wyeast. Different yeast strains have different characteristics – a “clean” beer like an American Blonde Ale will typically use a less expressive yeast strain than a Belgian farmhouse ale, or a German Hefeweizen.

Where Does Yeast Come From?

Yeast is everywhere in our environment. Malted grain is itself covered with wild yeast and bacteria, some of which can survive mashing temperatures. One reason that wort is boiled prior to fermentation is to kill any naturally occurring wild yeast or bacteria. After boiling, the wort is chilled to the optimum temperature for tempered yeast growth. This is typically somewhere between 50 and 70 degrees, depending on the type of yeast.

How Does Yeast Create Alcohol?

At a basic level, fermentation is the process where yeast converts sugars and other byproducts of the mashing process into alcohol, carbon dioxide, and other chemical compounds.

The life cycle of brewing yeast typically takes this arc:

1. Respiration: This is when the yeast is storing energy to reproduce.
2. Fermentation: The yeast now converts that energy into alcohol, carbon dioxide and flavors. 
3. Sedimentation: When fermentation is complete, the yeasts go dormant.