A-39: Varietal dependency of hop-derived water-soluble flavor precursors in beer

D. Vollmer (1), Y. Qian (1), G. Shellhammer (2), T. SHELLHAMMER (1); (1) Oregon State University, Corvallis, OR, U.S.A.; (2) Shellhammer Consulting, Corvallis, OR, U.S.A.

Hops
Friday, June 6 - 8:00 a.m.-9:45 a.m.
Level 4, Red Lacquer Ballroom

Work performed at Oregon State University and elsewhere provides evidence of water-soluble aroma precursors, such as terpenoid glycosides, existing in hops. This study examined varietal differences in the water-soluble aromatic fraction. Eighteen hop varieties were selected from 10 genetically distinct groups for inclusion in this study. During the winter/spring of 2013, Yakima Chief performed small-scale supercritical fluid CO2 extractions (SFE) of pellets from 18 varieties. The SFE was used to remove hop oils from the hop material so that an oil-free material could be used as a starting point for the water-soluble flavor precursor measurement. An aqueous extract of the spent hops was prepared and treated with a commercial enzyme blend containing glycoside-hydrolyzing enzymes. Control and enzyme-treated extracts were examined instrumentally using a stir bar sorptive extraction (SBSE)-GC-MS procedure and sensorially using a trained panel descriptive analysis. Bound aglycones (linalool, citronellol, nerol, beta-damascenone, geraniol, eugenol, and terpinene-4-ol) were released by the enzyme treatment of the aqueous spent hop extracts and resulted in significant and substantial changes to the aromatic and instrumental profiles. In general, the enzyme treatments resulted in less “meaty” and more “dark fruit” aromas and liberated measureable amounts of all aglycones. However, beyond those generalizations the responses were hop variety dependent, and furthermore, the variety dependency did not correlate with the variety groupings based on genetic pedigree. The hop variety responses to the enzyme treatment resulted in 4–5 distinctly different groups. Centennial and in some cases Columbus were two varieties that stood out from the rest. From an instrumental perspective these two varieties underwent unique changes as a result of the enzyme treatment. Sensory results showed that the attributes of the extracts are influenced by hop variety, and Centennial showed the greatest magnitude of change for several of the observed attributes. Partial least squares regression was used to predict sensory attributes based on the instrumental measurements; however, the best model produced by this analysis did not fully account for the variability in the instrumental (54%) and sensory (17%) data sets. Nonetheless, we observed that increases in citronellol and eugenol following the enzyme treatment were associated with increases in “citrus,” “floral,” and to a lesser extent “floral” and “overall” attributes.

Thomas Shellhammer is the Nor’Wester Endowed Professor of Fermentation Science in the Department of Food Science and Technology at Oregon State University (OSU), where he leads the brewing science education and research programs. His brewing research investigates hops and beer quality, hop-derived bitterness and its quality assessment, and the origins of hop aroma and flavor in beer. He directs the brewing education component of the Fermentation Science program at OSU and teaches courses about brewing science and technology, and beer and raw materials analyses, as well as an overview of the history, business, and technology of the wine, beer, and spirits industries. Thomas received his Ph.D. degree from the University of California, Davis, in 1996. During the 2008–2009 academic year, while on sabbatical leave from OSU, he worked at the Technical University of Berlin as a Fulbright Scholar and Alexander von Humboldt Fellow. Thomas is the International Section chair and a Board of Examiners member for the Institute of Brewing and Distilling, London, England; a member of the editorial board of the Master Brewers Association of the Americas Technical Quarterly and president-elect of the Board of Directors of the American Society of Brewing Chemists.

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