27. Terminal acidic shock inhibits sour beer bottle conditioning by Saccharomyces cerevisiae

Matthew Bochman (1), Adam Covey (2), Cody Rogers (1), Caleb Staton (2), Devon Veatch (3) ; (1) Indiana University, Bloomington, IN, U.S.A.; (2) Upland Brewing Company, Bloomington, IN, U.S.A.; (3) Ivy Tech Community College of Indiana, Bloomington, IN, U.S.A.

Technical Session 8: Yeast Stress & Performance
Monday, August 15  •  8:15–9:30 a.m.
Tower Building, Majestic Level, Majestic Ballroom

During beer fermentation, the brewer’s yeast Saccharomyces cerevisiae experiences a variety of shifting growth conditions, culminating in a low-oxygen, low-nutrient, high-ethanol, acidic environment. In beers that are bottle conditioned (i.e., carbonated in the bottle by supplying yeast with a small amount of sugar to metabolize into CO2), the S. cerevisiae cells must overcome these stressors to perform the ultimate act in beer production. However, medium shock caused by any of these variables can slow, stall, or even kill the yeast, resulting in production delays and economic losses. Here, we describe a medium shock caused by high lactic acid levels in an American sour beer, which we refer to as “terminal acidic shock.” Yeast exposed to this shock failed to bottle condition the beer, though they remained viable. The effects of low-pH/high-[lactic acid] conditions on the growth of six different brewing strains of S. cerevisiae were characterized, and we developed a method to adapt the yeast to growth in acidic beer, enabling proper bottle conditioning. Our findings will aid in the production of sour-style beers, a trending category in the American craft beer scene.

Matt Bochman received his B.S. degree in molecular biology from Juniata College in Huntingdon, PA, in 2003 and his Ph.D. degree in molecular, cellular, and developmental biology from the University of Pittsburgh in 2008 and was an American Cancer Society postdoctoral research fellow at Princeton University. Since 2013, he has been an assistant professor in the Molecular & Cellular Biochemistry Department at Indiana University in Bloomington, IN. During his 15 years in research labs, he has used various yeasts as model organisms to answer scientific questions, as well as to brew beer and hard cider. Recently, he has put his yeast skills to good use as a craft brewery and distillery consultant and co-founded Wild Pitch Yeast, LLC to supply yeast-related services to these industries in the American Midwest.