D. C. SHARP (1), T. H. Shellhammer (1); (1) Oregon State University, Corvallis, OR, U.S.A.
Technical Session 3 - Hop Aroma
Monday, June 15
8:30–10:15 p.m.
Fiesta 3,4,6,8
Non-volatile hop-derived aroma precursors contribute to aroma in finished beer. Specifically, glycosidically bound terpenoids extracted from hops during the brewing process are hydrolyzed to release volatile aglycones. Previous studies show that the complexity of hop aroma can be partly attributed to these water-soluble glycosides through yeast biotransformations. However, the effect of yeast strain on biotransformation has not been fully investigated. This study quantifies the hydrolytic activity of different yeast strains on glycosidically bound terpenoids and determines whether differences in these activities change hop aroma profiles in beer. β-Glucosidase activities for 80 different yeast strains were quantified as a measure of the glycoside hydrolysis capability of each yeast. 4-Methylumbelliferyl β-D-glucopyranoside (4-MUG) was used as a substrate and the fluorescence emission of the liberated aglycone, 4-methylumbelliferone, was measured and normalized by optical density. Bench-top fermentations were conducted with a subset of the initial population using yeasts exhibiting a range of glucosidase activities. After fermentation was complete, terpenoid contents in each beer were measured by solid phase micro extraction with GC-MS analysis. Yeasts were found to have a range of β-glucosidase activities from 0 U/L to ~250 U/L with an average of 95 U/L (1 U catalyzes the hydrolysis of 1 µmol substrate per min at pH 5). Increases in terpenoid levels as a result of yeast biotransformation were observed. For example, compared to unfermented wort, linalool contents increased between 45% and 78% depending on yeast strain. These results help explain the extent to which different brewing yeasts are able to contribute to hoppy beer aroma through the biotransformation of hop-derived compounds. In a broader sense, the results from this project will aid brewers in selecting yeast strains during recipe development and to better understand the contributions of yeast to hop-derived aroma in beer.
Daniel Sharp is a Ph.D. candidate in the Food Science and Technology Department at Oregon State University, focusing on hop studies being conducted in Thomas Shellhammer’s lab. He earned a B.A. degree from the University of Oregon and his master’s degree from Oregon State University. Daniel is the 2012–2014 recipient of the InBev Baillett-Latour Brewing Scholarship for his Ph.D. work toward identifying contributing factors of hop aroma in finished beer. He also enjoys backcountry skiing when the snow is good and time allows.
