Bryant Lo Re (1), William Deutschman (1); (1) Westminster College - Salt Lake City, Salt Lake City, UT, U.S.A.

Yeast, Fermentation, and Microbiology

Sales trends over the past decade have shown that high-gravity brewing has been a primary area of development in the craft beer market. Recently, however, there has been movement in the opposite direction, with “session beers” becoming a rapidly growing craft brewing sector. Breweries at the forefront of high-gravity brewing have introduced low-alcohol offerings, and new craft brewers who offer only lower alcohol session beers have entered the market and are doing well. A primary challenge faced in the production of a quality session beer is maintaining a strong, unique, and well-balanced flavor and aroma profile while keeping the malt content low, thus resulting in a flavorful yet only moderately alcoholic beer. To achieve this balance, brewers typically look to adjustments in malt content, creative use of non-fermentable adjuncts, and mash temperature adjustments to produce beers with higher residual carbohydrate content from low initial gravity worts. The purpose of this project is to create a strain of brewing yeast that will favor aerobic metabolism over anaerobic fermentation, thus producing a beer of similar flavor and aroma profile, but with lower than normal ethanol concentrations. A yeast with this ability would have great commercial application as it could represent a path to producing beers that satisfy the growing session beer market, as well as avoiding some of the impacts on personal and community health that beverages with high ethanol content can have. It has been well documented that the Crabtree effect in Saccharomyces yeast results in ethanol production even under aerobic conditions if sugar concentrations are high. Thus, even in the early aerobic stages of a fermentation, ethanol is being created. One potential solution to producing lower alcohol beers is to reduce the extent of the Crabtree effect, resulting in more efficient aerobic metabolism of wort before anaerobic fermentation begins in earnest. Thus, a higher gravity wort could be used and yet result in similar or lower final ethanol content. This would then leave a stronger malt profile and more residual body, meaning a more richly flavored session beer. Toward this goal, commercially available strains of Saccharomyces brewing yeast were treated with a chemical mutagen, plated on a media selective and fatal for yeast with a functioning copy of the alcohol dehydrogenase enzyme, and left to grow for 11-14 days at 30°C. Colonies were picked and assayed for ability to metabolize wort sugars while producing reduced ethanol concentrations. The initial gravity, final gravity and ethanol content of each fermentation was measured. We have isolated new yeast strains that are capable of producing a beer with similar final gravity to the initial commercial strain, but which produce 20% less alcohol by volume. This suggests these strains could be used to produce significantly richer and fuller bodied beers while still maintaining the low alcohol levels desired in session-style beers.

Bryant Lo Re is entering his senior year, attending Westminster College in Salt Lake City, UT. He is pursuing a degree in chemistry, with additional course work in biology and biochemistry. He became interested in brewing science and undergraduate research in the summer of 2015 when he began a research project under the guidance of Dr. William Deutschman.

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