Yeasts In Beer: What Does Yeast Do?

At one point during in this blog I delineated all beer types into two distinct groups: ales and lagers. Is this oversimplifying? Yes. But guess what? I had a good reason to do it:


Yeast is up there with mold in the category of things that I don’t completely understand and don’t have a burning desire to learn everything about. But both are types of fungi and I do love mushrooms on pizza. And I also love beer, which uses yeast as one the main ingredients.

The main yeast in beer, Saccharomyces cerevisiae, is the type of yeast used in baking, wine making and brewing. But there are various strains of this, much like there are different types of mold. Top-fermenting yeast is used for ales, and bottom-fermenting yeast is used for lagers.

Top-fermenting yeast, if you were wondering, works well in warmer temperatures. It got its name because the yeast rises to the top of the beer during the fermenting process.

Bottom-fermenting yeast, if you were still wondering, likes colder temperatures. It got its name because the yeast settles at the bottom of the brew.

And the other differences between how these yeasts work? Well, you can learn more by reading about lagers and ales. (Spoiler: they create different types of beer.)

But guess what! That’s not the only yeast involved in beer. No sir, not anymore.

Gettin’ Hyphae With Yeasts

Yeasts sometimes have little guys called hyphae, which is pronounced “hyphy.” I probably could have come up with a better joke or pun but I didn’t (get over it).

Ok, here’s how yeasts work: yeasts are alive and they love sugar. The more sugar they eat, the more byproduct they produce, which is alcohol and carbon dioxide.

Just think of alcohol as yeast poops and carbon dioxide as yeast farts, and you get the idea.

So, the alcoholic content and the fun fizziness of your barley pop comes from the yeasts. Without yeasts, you would just have a sweet, sugary, flat drink. The yeasts also produce a lot of the unique flavors you find in beer.

The neat thing is that we’re still learning about all the different yeasts and how they can make us better beers.

Being Picky With Yeast

In today’s modern world of brewing, brewers are able to use pure strains of yeast, giving them better control over beer.

But this wasn’t always the case. Back in the good old days (before people really started understanding yeast), most beer was a little sour. Why? Because yeast types were mixing together! This is sometimes referred to as spontaneous fermentation.

Where is this sour flavor coming from? Our good yeasty friend Brettanomyces Lambicus.

Brett, for those who don’t regularly drink funky farmhouse beers, is what we call both the flavor of the beer and the goo left at the bottom of the bottle. The goo is just the Brettanomyces yeasts.

What flavor does this produce, you ask? Why, the sour flavor!

So, if I were to revise the beer categories, I might say there are three types of beer: ales, lagers and sours. This is because they are using very different types of yeast.

Brettanomyces is making a huge comeback nowadays. For decades, brewers tried to get pure strains of Sacc. Today, brewers are looking for pure strains of Brett.

As brewers gain better knowledge of yeasts, there will be many more exciting beer flavors produced!

Thomas Short
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