Engineering of Brewing Yeast to Fight Diastatic Contamination in Beer
Faculty Mentor Information
Dr. Paul Rowley, University of Idaho; and James Mackenzie, University of Idaho
Presentation Date
7-15-2026
Abstract
Diastatic Saccharomyces cerevisiae strains pose a great challenge to brewing due to their active STA1 gene, which encodes a secreted glucoamylase. This enzyme causes unwanted fermentation of starches which leads to over-attenuation, off-flavors, and exploding packaging. Nearly half (49%) of surveyed U.S. craft breweries reported contamination, with 67% actively screening. This shows the urgent need for protective measures.
S. cerevisiae naturally produce antifungal killer toxins. The K1 toxin is highly effective, inhibiting over 90% of diastatic yeasts by binding to β-1,6-glucan receptors and disrupting membrane integrity. Using this mechanism offers a biological strategy to safeguard brewing.
We used rare-mating to introduce K1 toxin elements into brewing strains. This technique allows cytoplasmic mixing without nuclear fusion, preserving desirable brewing traits. Under selective growth, we isolated hybrid ale and lager yeasts expressing the K1 phenotype. Killer assays confirmed strong inhibition of diastatic contaminants, outperforming non-engineered controls. Preliminary tests measuring diastatic yeast growth in wort show that our hybrid brewing strain reduces contaminant levels more effectively than the original OYL090 strain. In wort seeded with 50,000 cells/mL of diastatic yeast, the OYL090 strain reached 3.3×10⁷ cells/mL by day three, while the hybrid strain only reached 1.3×10⁷ cells/mL. When seeded with 5,000 cells/mL, OYL090 reached 1.9×10⁷ cells/mL, compared to 8.0×10⁶ cells/mL in the hybrid. These results support the hybrid’s ability to suppress diastatic contaminants during fermentation.
Future directions include engineering hybrids with additional toxins (e.g., K2) and evaluating performance across beer styles. This strategy offers breweries a built-in defense system and minimalizes financial losses.
Engineering of Brewing Yeast to Fight Diastatic Contamination in Beer
Diastatic Saccharomyces cerevisiae strains pose a great challenge to brewing due to their active STA1 gene, which encodes a secreted glucoamylase. This enzyme causes unwanted fermentation of starches which leads to over-attenuation, off-flavors, and exploding packaging. Nearly half (49%) of surveyed U.S. craft breweries reported contamination, with 67% actively screening. This shows the urgent need for protective measures.
S. cerevisiae naturally produce antifungal killer toxins. The K1 toxin is highly effective, inhibiting over 90% of diastatic yeasts by binding to β-1,6-glucan receptors and disrupting membrane integrity. Using this mechanism offers a biological strategy to safeguard brewing.
We used rare-mating to introduce K1 toxin elements into brewing strains. This technique allows cytoplasmic mixing without nuclear fusion, preserving desirable brewing traits. Under selective growth, we isolated hybrid ale and lager yeasts expressing the K1 phenotype. Killer assays confirmed strong inhibition of diastatic contaminants, outperforming non-engineered controls. Preliminary tests measuring diastatic yeast growth in wort show that our hybrid brewing strain reduces contaminant levels more effectively than the original OYL090 strain. In wort seeded with 50,000 cells/mL of diastatic yeast, the OYL090 strain reached 3.3×10⁷ cells/mL by day three, while the hybrid strain only reached 1.3×10⁷ cells/mL. When seeded with 5,000 cells/mL, OYL090 reached 1.9×10⁷ cells/mL, compared to 8.0×10⁶ cells/mL in the hybrid. These results support the hybrid’s ability to suppress diastatic contaminants during fermentation.
Future directions include engineering hybrids with additional toxins (e.g., K2) and evaluating performance across beer styles. This strategy offers breweries a built-in defense system and minimalizes financial losses.