Yeast Fermentation and How It Creates Beer

As one of the oldest beverages known to man, we’ve come to understand pretty much every aspect of the science of beer brewing. Fermentation is the process that creates the alcoholic content of beer, but how does it actually work? The secret is the little microorganisms known as yeast. We’ll look into yeast fermentation and how it creates beer to understand this fascinating process a little better.

What Is Yeast?

As incredible as yeast is, its structure is remarkably simple. Yeast is a single-cell living organism, specifically Saccharomyces cerevisiae, that you can find almost everywhere. Technically, yeast is a fungus, and it’s incredibly small—microscopic, in fact.

Yeast is incredibly useful because of what it does when it meets up with sugar or starch. It eats these substances and breaks them down into alcohol and carbon dioxide. This is the process we know as fermentation, and we see it most commonly in alcoholic beverage making and baking.

Why Do We Use Yeast To Make Beer?

We already know that yeast makes alcohol particles as a result of its normal eating habits. By mixing up what brewers call a “wort,” which is a combination of ground up malt and grain products, brewers essentially create the perfect food source for yeast to eat, multiply, and produce alcohol.

This wort is combined with water and yeast and put in a stable environment to allow the yeast to go to work. It can take a decent amount of time, but the yeast will slowly take in the glucose molecules in the wort and produce alcohol and carbon dioxide. This turns an otherwise normal liquid into an alcoholic beverage.

Factors To Consider During Fermentation

Yeast can be a fickle creature; it is a living organism, after all. Managing yeast issues and making sure that their yeast stays healthy and usable is a major concern for most brewers. These are two of the biggest concerns when it comes to utilizing yeast for making beer.


Creating beer through yeast fermentation requires careful control over the temperature that the mixture stays at during fermentation. Most yeast strains prefer a slightly colder environment, but it can’t be so cold that it chokes the life out of them. Too much heat can kill yeast prematurely, so brewers need to watch their temperatures carefully.

Outside Contamination

Yeast is actually all around us, even just floating around in the air. This wild yeast is far more unpredictable than the stable strains that brewers use, so they do everything they can to prevent it from contaminating their batches. While their fermenters have places for carbon dioxide to escape, these tubes are carefully designed so oxygen and other yeast contaminants can’t enter the process.

By Dianne Pajo

Dianne Pajo is a writer based out of the Chicagoland area with a passion for music, combat sports, and animals. She enjoys competing in amateur boxing and kickboxing, but in her other leisure time, you can find her performing music around the city. She is also a dog mom of 2.