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O-29. Influence of harvest date on the chemical composition of Willamette and Cascade hops

Presenter: Daniel Sharp, Oregon State University, Corvallis, OR. Coauthor(s): Shaun Townsend, Yanping Qian, and Thomas Shellhammer, Oregon State University, Corvallis, OR.

Hop aroma development while the plant matures in the field is a rapid and dynamic process that requires a comprehensive, in-depth chemical and sensory analysis to maximize agronomic characteristics of interest to brewers. The complex aroma chemistry associated with hops in beers has been a confounding variable for the practical brewing scientist, and a deeper understanding of hop aroma development during cultivation is needed to elucidate important factors in hop aroma. The effect of harvest date, location, and variety on key chemical components of two commonly used aroma hop varieties in the craft brewing industry was investigated for the 2010 growing season. Willamette and Cascade hops were harvested at 3 time points within a 3 week window (early, normal, and late), from 3 different farms in the Willamette Valley and then analyzed for moisture, acids content, total oil content, and essential oil composition. Analytics were performed using standard American Society of Brewing Chemists methods of analysis. The response of analytes was dependent in many cases on the variety being examined, its location within the Willamette Valley, as well as time of harvest. Hop acids did not change appreciably over the time span of this study, while hop oil content increased hyperbolically to a plateau. Increases in oil quantity were strongly correlated (r > 0.80) with increases in α-pinene, β-pinene, myrcene, limonene, methyl heptanoate, linalool, and eudesmol concentrations. Relative percentages of many compounds did not correlate with later harvest dates, while location appeared to have an effect on oil concentrations for each variety at each time point.

Daniel Sharp is a master’s student in the food and fermentation science program at Oregon State University. His research is currently focused on hop studies being conducted in Thomas Shellhammer’s lab. Daniel’s primary area of study is the aroma compounds in hops and beer. Prior to joining the food science program at OSU, Daniel earned a B.A. degree in both Spanish and adventure leadership at the University of Oregon. After graduation he lived and worked in South America, first as a mountain guide in Venezuela and later as a brewer at the Center of the World Brewery, Ecuador’s only microbrewery at the time.