​​2020 Project Grant

​​University of Washington

Using genome sequencing to track changes in brewing yeast during serial repitching

Brewers typically purchase yeast and repitch it for up to 15 brewing cycles before starting again with a newly purchased starter. Continuing to use the yeast for additional cycles has the potential to decrease the costs associated with purchasing commercial yeast, but with possible tradeoffs in yeast behavior and beer flavor profile. These tradeoffs can have multiple causes, including physiological changes in the yeast, increased risk of contamination, and genetic mutations, which will be the focus of our project. Prior studies looking for such mutations over time have given contradictory and low resolution results. Modern genomics has the potential to greatly improve our understanding of how the yeast genome changes over the course of repitching. ​We have collected and sequenced three timecourses over 15-50 repitching cycles in collaboration with two Seattle-area breweries using the popular Chico family of strains. We have detected significant and reproducible chromosome changes that indicate that the yeast are adapting to modern brewery conditions, with implications for beer flavor. We propose to expand this study to additional breweries utilizing a wider variety of strains, including lager fermentations. We hope to use our data to provide practical guidance on how long it typically takes for new mutations to reach high frequency and thus potentially impact beer characteristics. In addition, we will isolate adapted clones to determine whether they might be better suited for particular brewery environments and so extend the time over which repitching can be performed. 

Project Objectives

We propose to sequence additional samples we have already collected from Postdoc Brewing, Druthers, Grimm Artisanal Ales, and a fourth Seattle-area brewery who would prefer to remain anonymous. We will collect samples from several additional breweries who have already committed to working with us, including Drake’s Brewing Company, Urban Chestnut Brewing Company, Alley Kat, Heroes Restaurant & Brewery, Elliot Bay Brewing, and Full Sail Brewing Co. These breweries use a range of strains, including the Chico strains from several different distributors, German Ale/Kolsch, London Ale, Burton Ale, and, most excitingly, various lager strains. We will also use the grant as an opportunity to recruit additional partners. Ultimately our goals are twofold: 1. Determine how many cycles of repitching can reliably occur without genetic changes reaching high population frequency, thus defining a timeframe over which repitching can be reliably employed. 2. Isolate strains that “take over” the fermenters after multiple rounds of repitching. These strains likely indicate adaptation to the modern brewery environment and so may be able to undergo extra repitching cycles without substantial genetic change, thus saving money. We will test the adapted strains for their brewing performance in homebrewing-scale laboratory fermentations to identify strains with the best characteristics for possible industrial deployment.

Principle Investigator​

Maitreya Dunham