Brett Taubman, Appalachian State University, Boone, NC, U.S.A.
Friday, October 13
Imperial Salon B
The volatile essential oil fraction of hops, approximately 0.5% to 3.0% of the dry weight of hop cones, is responsible for hop flavor and aroma and comprises a hydrocarbon fraction (mainly mono- and sesquiterpenes) and an oxygenated fraction (esters, alcohols, etc.). Virtually all of the hop oil constituents volatilize when hops are added to the kettle at the start of boiling. Even for late kettle additions, generally only the less volatile oxygenated fraction is imparted to the beer. As a result, dry hopping is the preferred method for imparting hop flavor and aroma (especially the more volatile hydrocarbon fraction) to beer by adding hop cones or pellets to beer in conditioning tanks postfermentation. Dry hopping, however, is far from ideal because of batch-to-batch inconsistencies in flavor and aroma, product losses from retention in the hop material, introduction of oxygen during the process, overall expense, etc. Steam distillation of the hop essential oils, therefore, presents a possible alternative to dry hopping that is more consistent, efficient, and cost effective. Unfortunately, the distilled hop oils may not impart the same hop character to beer as dry hopping. Because the oxygenated fraction is more soluble in beer than the hydrocarbon fraction, beers that have been dry hopped may have a different ratio of these compounds than beers with distilled hop oil added. Additionally, some compounds may undergo chemical transformation during steam distillation, producing a difference in flavor and aroma in beers with distilled hop oil additions compared to dry-hopped beers. The purpose of this study is to quantify the amount of dry hop and steam distilled oil additions for several hop varietals that imparts the same level of hop flavor and aroma in beer as determined by both sensory and instrumental analysis (GC-FID) and determine the differences in flavor and aroma imparted through dry hopping and steam distilled oil addition through both sensory analysis and a quantitation of the specific essential oil components with GC-FID and GC-MS. Thus far, a sensory analysis of Citra and Centennial hop treatments has been performed. A consumer panel was assembled and a sensory evaluation was conducted over a four-week period. Bitterness, sweetness, and astringency were chosen as major taste attributes and citrus, floral, and spicy as major aroma attributes indicative of experimental beers. Differences among experimental beers were determined for each selected attribute by qualitative descriptive analysis. The sensory QDA tests were established based on the three taste and aroma characteristics. Preference testing was also performed, although no statistically significant preference was found. In fact, statistical significance was only established in this initial trial for Centennial oil and dry-hop treatments with respect to citrus aroma. Additional tests will include more hop varietals and the instrumental component to quantify differences in amounts and specific oil components for the two treatments.
Dr. Brett Taubman is a faculty member of the A.R. Smith Department of Chemistry at Appalachian State University, engaged in instruction and academic research within chemistry and fermentation sciences. He has earned B.S. degrees in both finance and chemistry from the Pennsylvania State University and Montana State University, respectively, and a Ph.D. degree in analytical chemistry from the University of Maryland in 2004. Following his graduate studies, he worked as a postdoctoral research associate at the Pennsylvania State University before joining the chemistry faculty at Appalachian in 2007. Dr. Taubman has successfully developed a pilot instructional brewing facility on the ASU campus and currently serves as president of Ivory Tower, Inc., a 501(c)(3) nonprofit corporation with the mission of supporting research and education within the fermentation sciences. He helped to develop the four-year degree program in fermentation sciences and shares time between that program and the Chemistry Department. He has been brewing and teaching brewing sciences and technology for more than 10 years and is a member of the American Chemical Society, the American Society of Brewing Chemists, the Master Brewers Association of the Americas, and the Institute of Brewing and Distilling.