While hops tend to get all the glamor and attention these days, I strongly believe that the real stars of the show—what makes beer fascinating, delicious, and perhaps even nutritious, is yeast. And to think that humans brewed for thousands of years before we truly understood the critical role yeast plays in making our favorite concoction. Before the 1800s brewers knew they had to use the leftover sediment from the previous brew to make the next brew, but it wasn’t until Louis Pasteur finally identified yeasts as living organisms that we began to understand the important role yeast plays in beer. I for one, love brewing with all types of yeast strains. Tasting the difference from one strain to the next can be such a fascinating way to explore beer.
Domesticated Yeasts, aka Brewing Yeasts
For the most part, home brewers rely on two types of beer yeasts to make our magic happen. As always, temperature plays a big role in the fermentation process. Naturally, we can divide yeast strains into two major types, as determined by their temperature preferences. But it’s worth pausing for a quick moment to point out that on the very long timeline of brewing history, the fact that we have “domesticated” yeast is a rather new development. The differences in yeast evolved, or became more pronounced as brewers re-pitched the previous batch’s yeast into the next batch. This is what would eventually create “house character.” Over time, these “house” lines became their own unique strands, as they adapted to their native brewhouse.
Ale (Top-Fermenting) Yeast
Ale yeasts rise to the top of the fermenter during fermentation, hence the reason we call them “top-fermenting.” You’ll notice that this yeast creates a thick, yeast head at the top of the carboy in early fermentation. For home brewers, these yeasts are quite practical, as they ferment at temperature ranges between 10 to 25°C, depending on the strain. Most have an ideal temperature range of 18 to 22°C, which is reasonably easy for most of us to maintain, thanks to winter heating and summer air conditioning. You would use top-fermenting yeasts to brew ales, stouts, porters, wheat beers, Altbier, and Kölsch.
Lager (Bottom-Fermenting) Yeast
You guessed it, lager yeasts (sort of) ferment at the bottom of the fermenter. Temperature plays a big role in this. Lager yeasts do their thing at colder temperatures than top-fermenting strains, usually at temperature ranges between 7 to 15°C. As such, the yeasts don’t reproduce as quickly as their ale cousins and tend to settle at the bottom before ever making it to the top of the fermenter. And because lager yeasts ferment at colder temperatures, they inhibit the production of chemical products or off-flavours that can be pronounced in ales. This is why, for so long, we’ve identified a “cleaner” taste with lagers. You would use bottom-fermenting yeasts to brew Lagers, Pilsners, Bocks, Märzen, and Dortmunders, among others.
Now, before we take a look at all the beer yeast strains available to us, by type/function, we also need to understand a couple other important characteristics that may impact your choice of yeast strain.
This is the degree to which the yeast ferments the fermentable sugars in your wort. You could measure apparent attenuation from your hydrometer readings, but the ideal level of attenuation is a matter of beer style or personal preference. Some beer styles call for higher or lower levels of attenuation, which is just about how attenuation is categorized:
- High: 78% +
- Medium: 73% to 77%
- Low: less than 72%
A fancy way of referring to the clumping of yeast cells into clusters, which usually happens at the end of fermentation. The rate of flocculation determines how quickly the beer will clear. High flocculating yeasts sink to the bottom of the fermenter more quickly and produce a clearer beer.
Optimal Fermentation Temperature
As you likely guessed, this is the ideal temperature to ferment your beer at, for your chosen yeast. This one very important characteristic. I can’t stress how important it is to ferment your beer at the temperature your yeast prefers to do its work at. If the temperature is too low, fermentation could be slow to start or never reach its peak. If it’s too warm, you risk producing off-flavours that’ll make you want to pitch your beer down the drain.
You’ll want an indication of the type of flavours your yeast will contribute to your final product. Yeasts can do so much to transform the flavor of your beer, accentuating it maltiness or hoppiness, or adding fruity, sweet, or dry finishes. Understanding what flavors to expect will help you understand the finished beer.
Common Ale Strains
This one’s considered a jack-of-all-trades, an all-purpose yeast that produces a clean and neutral character. It’s durable yeast—it can handle temperatures as low as 13°C. It typically has medium attenuation and low to medium flocculation. Here are the most common strains available, by lab, and the manufacturers’ flavor profiles.
These yeasts produce pronounced fruity and estery character, often with hints of clove or phenolic notes. Of course, since these yeasts are predominantly used to brew Belgian beers, they have a high alcohol tolerance. If you love Abbey or Trappist beers, you’ll need one of these yeasts.
Gosh, where do we begin? This group is pretty versatile. London yeasts will give you a slightly more diacetyl or woody note, with a crisp, somewhat tart impression. Full-bodied yeasts will give you the fruitiness you’d expect from many English ales. And of course, you have Scottish yeasts which will accentuate the malty notes of your beer. If you’re looking to re-create a classic English Pub taste, you’ll want to start here.[
Sour beers aren’t for everyone, but if you’re willing to experiment and have some fun, sour beers make for quite an adventure in brewing. You’ll produce beers that are intentionally acidic and tart, with an obviously sour taste. So, if you’re in the mood for Belgian lambic, a Gueze or a Flanders ale, you’ll need one of these yeasts.
These beers pack a punch, usually hitting the 8-12% ABV mark, hence the word wine. Barleywines are, of course, beers. Just strong ones at that. Same with Imperial stouts, which are intensely malty and deeply roasted. In any case, when you get to ABV levels of this kind, you need a yeast strain that can cope in that environment. These ones are built tough for the job.
Given how popular IPAs are, it deserves its own category. Keep in mind, however, that a category as popular as this one has a wide spectrum of styles. While we often get hung up on the hop varieties and intensities (heck, that’s why most of us love IPAs), to make a kick-ass IPA, you’ll want to pick the right yeast strain to bring it all together and lend your beer some balance.
Like IPAs, this too is becoming an ever broadening category. Now you can find hoppy and bitter brown ales along maltier, nuttier versions. Brown ales are a surprisingly blank canvas to work from, with perhaps only the colour being (somewhat) a constant among all variations. Brown ales might not get all the glory and attention that IPAs get right now, but you really can’t beat a delicious brown ale. Give it a try for your next brew, using one of these yeast strains.
True to their style, Kölsch yeasts have good attenuation and lend the beer a crisp, clean finish, while giving profile to the malt/cereal characteristics that makes Kölsch a German favorite. Altbiers are darker than Kölsch and yield a smooth brew with medium carbonation and a good balance between malts and hops. Whether you’re going light or dark, you’ll need one of these strains to make your very own German ale.
Think you can make a better Irish stout than the folks at Guinness? Or are you hankering to try your hand at your own oyster stout? Do you have some fancy South American chocolate or coffee you want to toss into a dark brew? You’ll likely need one of these yeast strains to make your next epic stout or porter.
Just as sure as the sun rises, those of us living in cold climates will instantly order a tall glass of hefeweizen on the first day patios open. There’s nothing quite like sipping on a delicious wheat beer with overtones of banana and clove as you take in some sun after months spent in hibernation. Orange slice completely optional! Of course, you don’t need to wait for patio season. Any excuse will work, frankly.