O-44. The effect of kilning air temperature on hop essential oil content and aroma

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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