We Bow to Yeast

Fun Guys

There are many factors that determine beer flavor, but the most finicky and temperamental of them all is the yeast. Beer yeast fall under Kingdom Fungi, and as the name suggests, they are indeed fun guys. Before we get this party started though, a little beer science.

Fungal spores

Preparing the Ingredients

There are three main ingredients that go into making beer: water, barley, and hops. Yeast is the activating agent. The grain must first be partially sprouted; we call this process “malting”. Malting causes the plant to produce a starch-breaking enzyme that turns starch into simple sugars. Beer yeast can only consumer simple sugars, not starch.

Malt to Mash to Wort

The malted grain is first boiled or heated in water (a process called mashing) to activate various protein-digesting enzymes called proteases. Some brewers will heat the mash at different temperatures; this process (called multi-step mashing) results in a heavier beer, creamier mouth feel, and stiff foam. Hops can be added here or later on after the wort has cooled.

After the solids have been strained out of the mash, the remaining brown sweet liquid is called the wort. Once at room temperature, yeast is pitched and the entire batch of liquid is left alone for the magic of fermentation to proceed.

Small but mighty ale yeast:
Saccharomyces cerevisiae


Fermentation is a chemical reaction inside the cell that extracts energy from sugar in the absence of oxygen. The cell uses this energy to make proteins, to grow, and to reproduce. In beer making, we feed sugar to yeast, not to harvest the energy, but to drink and enjoy the waste products: carbon dioxide and ethanol. Yes, beer is liquid yeast waste.

Finicky Yeast

Brewing beer is like a chemistry experiment. The water contains minerals and solutes that can be adjusted, analyzed, and filtered. Brewers can pick the strain of hops that contain the perfect combination of alpha and beta acids. Barley can be mixed with other grains such as wheat and rye.

It’s All About the Yeast

There is, however, an element of artistry in brewing that has nothing to do with the brewer and everything to do with the yeast. During fermentation, yeast not only produce carbon dioxide and ethanol as waste products, they also produce hundreds of other molecules called secondary metabolites. These compounds give each batch of beer a unique flavor. A brewer can start off with the same type of water, the same grain bill, the same strain of hops, but adding a saison yeast versus an ale yeast will produce a completely different beer.

Factors that can anger or please the yeast include: time, temperature, light, extra sugar, low sugar, too much alcohol, other microorganisms (competing yeast or bacteria), oxygen, minerals, and even the material of the pot used for the mash. Some factors are controllable, that’s why breweries are so clean and sterile, but other factors can throw a batch of beer completely out of whack.

So next time you’re enjoying a beer, remember the fun guys who labored away: eating sugar, farting carbon dioxide, and peeing ethanol. Without them, that beer you are drinking would just be flat, bitter barley soup.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.