In this series, we’ve explored hops and malt. Now it’s time to take a closer look at yeast. As a homebrewer, you’re probably already familiar with the two main families of brewing yeasts, knowing that members of Saccharomyces cerevisiae (ale yeast) prefer warmer temperatures and tend to favor ester production, while members of Saccharomyces pastorianus (lager yeast) tolerate cooler fermentation temperatures and are more likely to produce sulfur compounds such as dimethyl sulfide (DMS). You’ve also faced the plethora of choices at your local homebrew shop.
At a finer grain of detail, yeast strains are often characterized based on their attenuation, flocculation, and alcohol tolerance. Attenuation (or “apparent attenuation”) refers to the percentage of wort sugars that the strain can process. Sweet wort is made up of many different kinds of sugar, and some yeasts have trouble with the more complex ones. That affects the final gravity and residual sweetness in your beer.
Flocculation is how well and how quickly the yeast cells settle out of the beer. Strains with high flocculation are likely less attenuative and may yield beers with some level of buttery/butterscotch flavors when the yeast settles out without driving off the naturally produced diacetyl.
Alcohol tolerance is fairly straightforward: It describes how much alcohol a yeast strain can tolerate before it stops working.
Beyond those base characteristics, strains can also differ by their propensity for generating certain noticeable flavor components such as clove and other phenols, fruity esters, diacetyl, and DMS. A yeast’s performance can be affected by pitching rate, oxygenation, and fermentation temperature, but it helps if you understand the basic character. That’s the knowledge you need to choose the right yeast for your next batch.
Most of us start with a shortcut and just go by the name (e.g., we choose a Kölsch strain when we’re planning a Kölsch). But if you’re brewing an ESB, there are several English/British ale yeasts to pick from, so you need to look a little deeper. The next level is to read the descriptions and style advice that the manufacturer offers. All of the mainstream yeast companies provide those basic qualities (attenuation, flocculation, alcohol tolerance, and perhaps an ideal fermentation temperature range), along with general descriptions of the character.
That’s quite useful, but it can still be challenging to differentiate strains. For example, White Labs WPL820 Octoberfest/Märzen Lager Yeast and their WLP920 Old Bavarian Lager Yeast are pretty similar, with each favoring malty lager styles.
Real-life sensory evaluation is necessary to make those descriptions more real and to dig deeper into the nuances. We’ll get that experience with another simple experiment. This process will give you a more visceral sense of all of those technical terms and the generalizations in the descriptions. “Apparent attenuation” may be hard to connect with on the printed page, but the difference is easy to understand when you taste your samples.
We could just shotgun the available yeast strains and contrast a wildly divergent set, but it’s better to pick a target beer style (in this case, pale ale) and choose related strains of yeast. Here’s a list I came up with that’s primarily focused on Wyeast strains, along with a couple of SafAle choices:
- Wyeast 1056 American Ale
- Wyeast 1272 American Ale II
- Wyeast 1332 Northwest Ale
- Wyeast 1217PC West Coast IPA
- Wyeast 1099 Whitbread Ale
- Wyeast 1318 London Ale III
- Wyeast 1335 British Ale II
- Wyeast 1098 British Ale
- Fermentis SafAle S-04
- Fermentis SafAle US-05
This set contrasts American and British strains, as well as liquid and dry yeast. Another alternative would be to choose a mix of Wyeast and White Labs yeast strains to see whether equivalently named strains behave the same.
As with any experiment, we want to reduce the variables and focus on the yeast alone. We’ll use a single recipe to share across the set of yeast strains, and we’ll ensure that all of them ferment at the same temperature.
Any style will do; you might want to pick a recipe you brew regularly. For our purposes, I’ve selected a basic extract pale-ale recipe that will provide a simple canvas on which to compare yeasts (see “Base Pale-Ale Recipe,” page 46). Whichever route you decide to take, follow the directions to brew a full 5 gallons (19 liters) of wort up to the point where you chill the wort, but before you pitch the yeast. From that point, we’ll take a similar mini-batch approach to our earlier learning labs.
After chilling the wort, split the batch into ten 1-gallon (3.8-liter) glass jugs, filling each one about halfway, so that you have ten 0.5-gallon (1.9 l) samples, each of which will get its own yeast strain. (If you prefer a smaller field for comparison, you could split it five ways instead of ten). As you’re pitching the appropriate yeast in each container, use a full package of liquid yeast or a half package of dry yeast. Be sure to label each sample so you can easily keep track.
Ferment all of the mini-batches at the same temperature (aim for about 68°F/20°C). Once fermentation is complete, bottle each mini-batch with about 0.4 oz (11 g) total dissolved priming sugar.
After a couple of weeks in the bottle for carbonation, it’s time for taste testing. Look over the yeast profiles for your selection of strains. Read through the descriptions, then put them in reverse order by apparent attenuation. While most of them should be fairly close, sampling from drier (higher attenuation) to sweeter (lower attenuation) reduces the chance that the drier samples will seem harsh.
Pour the first beer and take a good sniff. First, you should focus on fermentation character: look for fruity smells or buttery diacetyl, maybe a hint of sulfur. For the yeasts listed above, you’re unlikely to get phenols or DMS. With your second whiff, consider the malt and hops expression, as well as the balance between them. Write down your impressions, capturing as much qualitative detail as possible.
Follow the same approach for your first couple of sips: esters and diacetyl first, then the beer as a whole. In addition, get a sense of the body and residual sweetness. When you swallow, how are the finish and aftertaste? Is the finish crisp and clean, soft and lingering? Is the aftertaste clean or yeasty? At this point, you should also look at the beer and assess its clarity.
Now, pull it all together to see how the pieces fit. Hazy or cloudy beers will often have more yeast bite, or in milder cases, the finish will be softer. Higher esters will also decrease the crispness of the finish. After you’ve got a good sense of the beer, review the yeast profile again and see whether your sensory notes are in line. As you move on through the series, you’ll get a better sense of how the strains differ. In particular, the balance is likely to shift from hops character to malt as the apparent attenuation drops. Once you’ve reviewed them all, it’s time to do some head-to-head comparisons.
Across the spectrum, it’s very likely that some will stand out as unique, either for good or ill. Try your favorite against your least favorite and see if you can identify why you prefer the one. Is it an off-flavor or a less-pleasant aftertaste in the least favorite? It may be that the least favorite pushes the beer a little out of style. It’s also good to pick two that seemed fairly similar and see what details separate them. For example, the ester levels may be comparable, but the nuances of the fruitiness between banana and stone fruit may distinguish them. Alternatively, one may favor the hops a little more strongly.
Aside from giving you a more intuitive sense of yeast characteristics, this technique can help you decide which strain complements a given style best for your own personal taste. This comes in handy when you’re trying to take a recipe to the next level. After you’ve fine-tuned a recipe over several batches, it’s worthwhile to try this split-batch approach to see how changing the yeast impacts the beer. Broadening your choices is especially helpful if you’re in the habit of using the same set of yeasts for most of your beers.
Another variation on this experiment is to use a smaller set of yeasts but introduce the additional variation of fermentation temperature. This is most interesting when applied to German weizen or Belgian strains, because their character tends to be more temperature dependent in terms of whether they favor esters or phenols. Try this out a time or two, and you’ll have a much stronger feel for yeast character. This will not only help you make better beer; you’ll also have a deeper appreciation for all the beer you drink.