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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