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HomeEnvironmentDeadly Yeasts: The Unexpected Heroes in Craft Beer Brewing Challenges

Deadly Yeasts: The Unexpected Heroes in Craft Beer Brewing Challenges

Diastatic yeasts, specifically strains of Saccharomyces cerevisiae, can turn into a serious issue for craft brewers if they inadvertently contaminate the beer. These unique strains release an enzyme called glucoamylase, which can convert dextrins into simple sugars. This process not only increases the alcohol content of the beer but can also alter its flavor, and in severe cases, result in bottle explosions.

This week, an interesting potential solution might have emerged. Researchers have revealed in Applied and Environmental Microbiology that other yeast strains might help combat the diastatic yeast issue. They found that certain proteins known as killer toxins, which are produced by various S. cerevisiae strains, can inhibit diastatic yeasts and potentially alleviate the problem.

Microbiologist Paul Rowley, Ph.D., from the University of Idaho, expressed the financial burden of dealing with a diastatic contamination, stating, “When faced with this issue, breweries often have to discard the affected beer, which is costly. Our research demonstrates that adding killer yeasts at the point of contamination may serve as a remediation technique to prevent diastatic strains from proliferating.”

Diastatic strains of S. cerevisiae are notably utilized in crafting Belgian-style saison beers, characterized by a higher alcohol content compared to other varieties. Rowley pointed out the complication arises when these strains inadvertently mix with pale ales and initiate unplanned secondary fermentation. While many breweries implement thorough monitoring to avoid contamination, these rogue strains can still get through.

Rowley explained, “If you were to examine these strains on an agar plate, you wouldn’t be able to visually distinguish them. The sole differentiating factor is that diastatic yeasts possess a genetic variation that enables them to further break down residual starches. Visually, yeast appears similar across the board.”

While larger breweries often sidestep this complication by pasteurizing their beer, this procedure can be quite pricey. Additionally, some small-scale brewers worry that pasteurization might alter the beer’s flavor, according to microbiologist Nicholas Ketchum of Rhinegeist Brewery in Cincinnati, Ohio, who co-authored the recent study. One of his roles at Rhinegeist is monitoring for diastatic contamination.

The research project first kicked off several years back when Ketchum taught a class on applied microbiology and brewing at a local community college. As he prepared a lecture focused on wild yeasts and killer toxins, it dawned on him that these proteins could be a cost-effective solution for diastatic contamination. Following a few experiments and sharing early findings at the World Brewing Congress in 2020, Ketchum’s discussion on a beer brewing podcast captivated Rowley’s interest.

In Rowley’s lab, researchers, including undergraduates Victor Zhong and Ximena Garcia, tested 34 diastatic yeast strains against 8 known killer toxin-producing Saccharomyces strains. They discovered that the K1 toxin was particularly effective, preventing growth in over 91% of the diastatic strains assessed.

The next focus of their research, according to Ketchum, is to delve deeper into understanding the underlying mechanisms and ways to make this knowledge widely applicable for craft brewers. He highlighted, “There are many more unknown factors than established ones” regarding how this works. For instance, the effectiveness of the toxins appears to hinge on the overall yeast quantity present, beyond just the diastatic strains. Rowley is also currently exploring the prevalence of this issue among smaller brewing operations.

Rowley remains committed to studying killer toxins, a topic which has not received extensive research attention. “The complexity of yeasts is greater than we might assume,” he concluded.