Contributions to hop aroma in beer from the water-soluble fraction of hops

Technical Session 01: Hops I Session
Thomas H Shellhammer, Oregon State University, Corvallis, OR, USA
Co-author(s): Daniel Sharp, Yanping Qian, and Michael Qian, Oregon State University, Corvallis, OR, USA

ABSTRACT: Hop aroma in beer is complex. While hop oils contain over 300 different components that can contribute to beer flavor, their high volatility results in little hop oil being retained in the finished beer. Yet beers produced using a long boil do have significant hop flavor and aroma. While terpene alcohols and oxidation products (epoxides) can contribute flavor, another hypothesized source of this aroma lies in glycosidically bound aromatic compounds such as glucosides and arbinoglycosides of alcohols, monoterpene alcohols, and ketones. During fermentation, and more likely post-fermentation, yeast may hydrolyze the sugar moieties for energy and, thereby, release the volatile aglycone, thus contributing to hop aroma in beer. This study examined the impact of the water-soluble fraction from four different American hop varieties (Simcoe, Centennial, Citra, and Cascade). Samples of each variety were extracted using supercritical fluid CO2 extraction, and the resultant extract and spent materials (along with the starting material) were dosed at (1 g/L) in hot wort to produce approximately 40 L of finished beer. Volatile analysis of beers was performed using a stir bar sorptive extraction (SBSE) with compound identification via GC-MS-FID. Key aroma compounds, alpha-pinene, beta-pinene, myrcene, limonene, linalool, caryophyllene, humulene, and terpineol were identified using selective ion monitoring mode and quantified. The linalool concentrations in the spent hopped beers were significantly higher than the other two treatments and were high enough to contribute to hop aroma. Principal component analysis revealed clustering of beers into separate groups by type of hop material (pellet, extract and spent). The sensory descriptive data identified prominent differences among the form and variety treatments. The spent hop treatments produced beers that had perceptible hop aroma. In one instance, Simcoe, the spent treatment resulted in beers that had higher aroma than extract and pellet treatments from other varieties. The intensity and nature of the hop aroma in the spent treatments was hop-variety specific, making it difficult to make a blanket statement regarding the water-soluble components of hops and their impact on hop aroma across all varieties. Nonetheless, there is sufficient evidence that in Citra and Simcoe hops the spent material contains substantial hop aroma or precursors thereof. These results point to the importance of non-oil contributions to hop aroma in some varieties.

Thomas Shellhammer is the Nor’Wester Professor of Fermentation Science in the Department of Food Science and Technology at Oregon State University, where he leads the brewing science education and research programs. His brewing research investigates hops and beer quality. 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. Tom 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. Tom is a member of the Board of Examiners for the Institute of Brewing and Distilling, London, England, and the chair of the Editorial Board of the MBAA Technical Quarterly.