Kent Johnson (1), William Deutschman (1); (1) Westminster College - Salt Lake City, Salt Lake City, UT, U.S.A.
Yeast, Fermentation, and Microbiology
Brettanomyces family, has risen dramatically, in part because yeast strains from the Brettanomyces
family are reputed to be able to metabolize more complex sugars, thus
“drying out” residual extract in high-gravity beers and leaving a beer
with lower body and mouthfeel. While the maltotriose fermentation
profile of more traditional yeasts such as Saccharomyces cerevisiae and S. pombe is well known, the ability to metabolize maltotriose or larger dextrins by yeasts in the Brettanomyces
family is less well characterized, with conflicting information in the
literature. There is very little information available on the metabolic
ability of Brettanomyces yeast with respect to maltotetraose or
larger glucose polymers. The objective in this study was to begin the
process of determining the metabolic preferences and abilities of
several commercially available Brettanomyces strains. Standard
malt extract wort was prepared and inoculated with each yeast strain.
The wort was aerated and fermentation was allowed to proceed to
completion. The sugar profile of the fermentation mixture was monitored
periodically using HPLC with an Aminex HPX-87H or Aminex HPX-42A column
and ELSD detection. We found that the ability to metabolize maltotriose
was much lower than had been previously reported under primary
fermentation conditions. Additionally, the commercially available
strains of Brettanomyces show little metabolism of larger glucose
polymers, even with fermentations lasting several months. This work
suggests that final fermentation or aging of finished beer in the
presence of these yeasts may not be having the effects on residual
extract that are commonly accepted and that the “drying out” of beer
exposed to Brettanomyces may be due to other mechanisms.
Kent Johnson is currently pursuing a B.S. degree in biology, with a
minor in chemistry, at Westminster College. At present, he is working
on research in the fields of brewing science and institutional strategy,
with plans to attend medical school after his undergraduate years.