Killer Yeasts in Brewing: Limitations of Detection Methods and Implications for Fermentation Performance

Webinar Summary

Killer yeasts strains that secrete protein toxins lethal to competing yeast are well documented in winemaking but remain under-recognized in brewing. As the industry expands into non-traditional strains and category innovation, the risk of introducing killer-positive yeast into shared brewing infrastructure is growing. This talk reviews the biological basis of the killer phenotype, then presents original fermentation data showing that the industry-standard ASBC Yeast-8 plate assay can fail to predict real-world outcomes: a lager strain that tested "insensitive" on the plate was ultimately replaced by over 93% in actual fermentation, following just 10% initial contamination. The talk closes with a proposed complementary fermentation-based assay and practical recommendations for screening and monitoring yeast strains in brewing operations.

Learning Objectives

After participating in this webinar, attendees will be able to:

• explain the biological basis of the killer yeast phenotype, including why it is not reliably predictable from genome sequencing alone.
• analyze the limitations of the ASBC Yeast-8 method in predicting fermentation outcomes, using real experimental data.
• compare phenotypic, molecular, and quantitative detection methods for killer yeast and understand what each does and does not tell you.
• apply practical screening and monitoring recommendations when introducing non-traditional yeast strains into a brewing operation.

Webinar Presenter

Moderator: Spencer Weeks | Great Lakes Brewing

Hatice Morris

Corporate Brewing

Hatice Morris has spent approximately 15 years in the fermented beverage industry with a focus on fermentation and microbiology, including a background in wine and R&D biological product and fermentation development. She later joined Molson Coors Corporate Quality as a yeast and fermentation scientist, where she managed the company's yeast bank and supported yeast supply to breweries while leading projects on the company's long-term yeast strategy, before moving into Corporate Brewing, where she now supports breweries directly on yeast and fermentation performance as the Yeast and Fermentation SME. Her presentation builds on a study she first shared as a poster at the World Brewing Congress in 2024.