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