Examine the top 5 performance indicators to choose the right strain for the job.
Yeast strains affect fermentation time.
While the magic of fermentation has been enjoyed by man for an estimated 10,000 years, for close to 9,700 of those years it was never fully understood or appreciated. Knowing only that the frothy barm in their fermenters was somehow responsible for the creation of alcohol, early brewers christened it “godisgood.” The invention of the microscope in the late the 1600’s opened up a whole new world of possibilities in the brewing industry. Yeast was not only recognized for its impact on the fermentation process, it was identified and categorized as never before. Hundreds of different yeast strains were isolated and classified. Microbiologists eventually placed the various strains of brewers’ yeasts in the genus saccharomyces, meaning “sugar fungus.” Today there are scores of yeast strains in this category alone.
Beyond simple yeast selection, brewers are concerned about specifics of their yeast supply, including viability, cell counts, pitch rates and batch-to-batch consistency.
Lab testing ensures batch-to-batch consistency.
Ultimately, you’ll want to examine specific performance indicators to ensure you choose the right strain for your craft beverage. Here are the top five to consider:
1. Attenuation
One of the dictionary definitions of attenuation means “reduce in thickness; make thin;” knowing how much a particular yeast strain reduces the thickness of your wort via fermentation should be of great interest to you. Attenuation is not just about creating more alcohol in your beer, but also about the beer’s taste and mouthfeel.
Be aware that there are several yeast strains, ale and lager like, that may attenuate as little as 65 percent, but when the beer style calls for it, there are a select few strains that can attenuate as high as 85 percent. Choose wisely.
2. Flocculation
Flocculation may not seem like a huge deal, and perhaps it’s a bit lower on the performance indicator scale, but it’s important nonetheless. The clumping up and settling out of spent yeast in many ways determines how a beer ferments, looks and tastes. If the yeast flocculates too early, the beer won’t be fully attenuated and will likely taste too sweet (worty); if a yeast floccs too slowly or not at all, the resulting beer with be cloudy and yeasty tasting.
Yeast flocculation can be described as being high, medium, or low. High flocculators start to aggregate within the first three to five days of fermentation and may have to be roused to finish the job. Medium flocculating yeast typically start flocculating between the sixth and 15th day of fermentation; these are good for a clean and balanced beer flavor profile. Low flocculators, like German hefeweizen yeast, tend to start clumping into the second week of fermentation; most wild yeasts, like Brettanomyces, are also low flocculators.
Ale yeast strains can be found in all three of these categories, while most lager yeast strains are considered medium flocculators.
3. Temperature Range
Most yeast strains are sensitive to the temperature at which they work and many have a sweet spot at which they work best. Knowing these ranges and providing your yeast with the appropriate fermentation temperature can work wonders for your beer.
The vast majority of American and British ale yeasts are very comfortable working in the 65 to 70 F range, with a few of them creeping up to about 72 or 73 F. The vast majority of lager yeasts, as you would expect, perform best in the 50 to 55 F range; the notable exception is the California Common style yeast, which prefers a warmer environment (65 F or so). Belgian yeasts, on the other hand, not only like it warm, but perform best at higher temps. Upper 60s to lower 70 F are typical for most of these strains, but there are still others that prefer to bathe in wort that is 75 F and above. Some Saison yeast strains even like it when the thermostat hits 80 F.
4. Alcohol Tolerance
It’s an odd quirk of nature that yeast can actually hinder its own performance due to a byproduct of its own making (otherwise known as alcohol toxicity). Yeast can only continue its gluttonous feast on maltose as long as the alcohol content within the beer doesn’t rise above its own tolerance for it.
The average saccharomyces strain can easily ferment up to five percent alcohol, with the possibility of nearly doubling that amount -depending on the yeast’s health and fermentation conditions. There is another dozen or more strains that routinely ferment up to seven or eight percent, with the possibility of reaching the 12 or 13 percent plateau under optimum conditions. Within the Belgian/Specialty category, it’s not unusual for some strains to produce 10 to 15 percent, while a select few strains are capable of reaching 20 percent ABV.
5. Flavor and Aroma
When everything is said and done (and fermented), nothing is going to matter as much to you or your customers than the way your beer smells and tastes. In addition to all the aforementioned ways to measure a yeast’s performance, none matters as much as the flavor and aromatic profile created by the yeast.
The most common of these aromas and flavors are in the form of esters, phenols and alcohol. Esters are recognized as being fruity, phenols as being medicinal or spicy, and higher “fusel” alcohols (i.e., propanol, butanol), when in abundant amounts, can exhibit floral, wine-y or even solvent-y notes. Lesser discussed flavors and aromas include ketones (of which diacetyl is an example) and fatty acids (often associated with staling character in beer).
Note that lager yeasts tend to be more neutral in all of these areas—especially when it comes to esters and phenols—but may also produce more sulfur character than ale yeasts. Also note that most of these aroma and flavor characteristics can be controlled by the previously mentioned performance indicators in combination with the yeast’s flavor profile.
This may all seem like a lot to consider when choosing which yeast strains to employ at your brewery, but nothing is as important to beer quality. These decisions can affect nothing less than your brewery’s reputation and your livelihood.
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