Sam Dulski, Westminster College, Salt Lake City, UT, U.S.A.
Coauthor(s): William Deutschman,
Salt Lake City, UT,
Yeast, Fermentation, and Microbiology
It is common industry practice for breweries to serially repitch yeast for many generations, as the yeast remains healthy and viable through successive fermentations. Reproducible attenuation and ethanol levels indicate that the metabolism of simple sugars such as maltose and glucose remains unchanged through this process. The literature reflects this observation. However, there has been very little information provided in literature on the metabolic activity of yeast as it ages in respect to the larger glucose polymers such as maltotriose, maltotetraose, and higher molecular weight dextrins. However, these are fundamental to brewing wort, though they are often considered poorly or non-fermentable. The objective of this study was to analyze the metabolic activity for complex glucose polymers by the Saccharomyces yeast on the maltotriose and larger glucose polymers over the course of repeated generations of serially repitched yeast. Unfermented wort was obtained from a local brewery and pitched with a strain of commercially available ale yeast, and fermentation was allowed to proceed to completion. Samples were taken throughout the fermentation process and the sugar content as a function of time was determined for all glucose polymers from n=1 to n=9 using HPLC with an Aminex HPX-42A column and ELSD detection. We found that yeast metabolizes the simple sugars glucose and maltose very well as it ages. However, complex sugar metabolism appears to change as yeast proceeds through successive fermentations. Our results show that some larger glucose polymers appear to be metabolized more effectively in later generations, while maltotriose appears to be metabolized less effectively in those later generations. This work suggests that yeast metabolism of higher order glucose polymers changes as yeast is serially repitched. This indicates yeast generation number may have a larger impact on flavor profile and packaging stability than has been previously understood.
Sam is an undergraduate biology major at Westminster College in Salt Lake City, Utah.