Presenter: Thomas P. Nielsen, Sierra Nevada Brewing Co.,
Chico, CA
Coauthors: Val Peacock, Hop Solutions, Inc., Edwardsville,
IL; Scott Garden, John I. Haas, Yakima, WA; Patrick Smith,
Loftus Ranches, Moxee, WA
During the 2012 hop harvest, the craft brewers hop quality
group (HQG) conducted a study focusing on drying air
temperature and aroma quality of dried hops. The commercial
method of drying hops in the United States utilizes an upward
flow of dry, heated air through a single tier, or bed, of hops.
Variables, such as air velocity, air moisture content, bed depth,
and air temperature contribute to the effectiveness of drying
and the resulting aromatic, physical, and storing properties of
dried hops. The effects of air temperature were studied in two
hop varietals and two hop kilns located in the Yakima Valley
in Washington. The primary goal of the study was to gauge the
overall quality effect of drying hops at 130 and 150°F. Results
show a wide range of moisture contents from the bottom to
top bed heights in both 130 and 150°F dried hops; however the
stratification was significantly greater in 150°F dried hops. The
total essential oil content for Citra hop samples showed greater
losses in the bottom and middle third of the drying beds,
whereas Cascade samples were uniform in total essential oil
content throughout the drying bed depth. A statistically significant
number of samples was analyzed by SPME-HS-GCMS,
along with multivariate analysis, inferring quality implications
of drying hops at 130°F versus 150°F. Caryophyllene oxide
proved to be an excellent marker for oxidation incurred by the
drying method. Qualitative measurements of caryophyllene
oxide, as well as other volatile hop components, are greatly
elevated in 150°F hop kiln samples compared to 130°F hop kiln
samples. These results outline some major differences produced
by varying air temperature when drying hops. Further study of
the brewing quality of hops dried at low and high temperatures
is needed in a follow up of this study.
Thomas (Tom) Nielsen has been working in an R&D capacity
at the Sierra Nevada Brewing Company for more than nine
years. Much of his work has involved basic and applied flavor
research on hops and malt. Prior to starting his career at
Sierra Nevada, Tom obtained a B.S. degree in food science
and technology from Rutgers University, focusing on food
chemistry. Tom is currently the technical chair of the Hop
Quality Group, as well as Sierra Nevada’s representative to the
Hop Research Council, American Malting Barley Association,
and Brewing and Malting Barley Research Institute.
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