Ask the Experts: Belgian Yeast Strains
Our “Ask the Experts” column poses your homebrewing questions to industry experts. In this issue’s column, we asked Phil Leinhart, brewmaster at Brewery Ommegang in Cooperstown, New York, for some advice on Belgian yeast strains.
A CRAFT BEER & BREWING READER
recently asked us the following question:
What are the differences between the various Belgian yeast strains? How do I choose the right one? With the vast number of yeast strains available to today’s homebrewer, it’s easy to get confused. “Belgian yeasts are incredibly diverse. The best place to start is to identify the technical performance characteristics you want for your homebrew: things such as optimal fermentation temperature, attentuation, and flocculation,” says Leinhart.
A yeast’s optimal fermentation temperature is actually a range of temperatures at which that yeast strain performs best. Aiming for a temperature below this range may stall the fermentation, while fermenting substantially above the temperature range can encourage the yeast to create unwanted flavors and aromas. Belgian yeast strains tend to work well at typical ale temperatures, 62–68°F (16–20°C), but some saison strains can tolerate temperatures approaching 100°F (38°C)!
Attenuation is a value that indicates the percentage of available wort sugars a yeast strain is likely to ferment. Highly attenuative strains can eat through 90 percent or more of the available sugars, while lowattenuating yeasts might barely get through 60 percent. Attenuation also depends on other factors, such as wort composition and fermentation tempera- ture, but all other things being equal, attenuation is a good metric with which to compare two yeast strains. All yeasts are different, but as a general rule, Belgian strains tend to be big attenuators relative to other broad classes of yeast.
Flocculation refers to a yeast strain’s tendency to clump together and drop out of suspension. Highly flocculent yeast cells readily fall to the bottom of a fermentation vessel at the end of fermentation, leaving behind brilliantly clear beer. Less flocculent yeast, on the other hand, may remain in suspension even after fermentation has come to an end. While Belgian strains tend to be mildly to moderately flocculent, this certainly isn’t a rule.
“We ferment Brewery Ommegang’s Glimmerglass, a Belgian saison, with a very flocculent yeast strain,” notes Leinhart. “The cells readily clump together into a slurry on the bottom of the fermentation tanks.”
Flocculation and attenuation are loosely correlated in that yeast cells that remain suspended are more likely to fully ferment than yeast cells that drop out. The relationship isn’t absolute, but it’s a good rule of thumb.
To compare these technical specifications, Leinhart recommends contacting major yeast suppliers such as White Labs, Wyeast, and the Brewing Science Institute. These microbiology labs publish yeast performance characteristics on their websites and are always happy to answer questions about every brewer’s favorite microbe.