J. D. Cook (1), W. A. DEUTSCHMAN (1);
(1) Westminster College, Salt Lake City, UT, U.S.A.
Maltotriose is a major constituent of brewing wort and is metabolized poorly by many strains of brewing yeast. The presence of residual extract in finished beer can have significant impacts on flavor, packaging stability, and resistance to spoilage bacteria. Recently the popularity of beers brewed or aged with non-traditional yeast strains, particularly in the Brettanomyces family, has risen dramatically. While the maltotriose fermentation profile of more traditional yeasts such as Saccharomyces cerevisiae and S. pombe is well known, the ability to metabolize maltotriose by yeasts in the Brettanomyces family is less well characterized. The objective in this study was to begin the process of determining the metabolic preferences and abilities of several non-traditional yeast strains such as B. bruxellensus, B. custersianus, and S. ludwigii in comparison to that of a commonly used strain of S. cerevisiae. 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 column and ELSD detection. We found that the ability to metabolize maltose and maltotriose varied widely between different yeast strains. Whereas S. cerevisiae is known to consume glucose, maltose, and maltotriose, we found that neither B. custersianus nor S. ludwigii were able to metabolize maltose, but were able to clear glucose and maltotriose efficiently from the media. This work suggests that final fermentation or aging of finished beer in the presence of these yeasts could be a useful tool to assure complete fermentation of maltotriose, increase package stability, and add protection against spoilage bacteria.
William Deutschman earned his Ph.D. degree in chemistry in 2001 at the Institute of Molecular Biology at the University of Oregon. From 2001 to 2006, he taught biochemistry at Plattsburgh State University in Plattsburgh, NY. In 2006, he moved to Westminster College in Salt Lake City, where he currently teaches chemistry, biochemistry, and brewing science, while also pursuing research projects with undergraduate students in the areas of brewing and fermentation science.