The effect of hop processing and exposure time on dry hop aroma extraction

Analytical Session
Peter H Wolfe, Oregon State University
Co-author(s): Thomas Shellhammer and Michael Qian, Oregon State University, OR, USA

ABSTRACT: The rate of hop aroma compounds extracted from Cascade hops during dry hopping was studied using both an unhopped beer and a model beer system devoid of malt and yeast aromas. Cascade hops pelletized by four different processors yielded different particle size distributions and pellet densities. These pellets, as well as whole hops, were dosed into a degassed medium (water, 6% [v/v] ethanol, pH 4.2), and the hop aroma extraction was measured periodically over a 1 week period. Solid phase micro-extraction (SPME) followed by gas chromatography (GC-FID) was used to analyze the levels of aroma compounds in the extraction medium. Variation in hop pellet physical properties did not significantly impact the extraction rate of hop volatiles such as linalool, geraniol, limonene, and myrcene, with one exception. One treatment showed an increased absolute concentration of geraniol. Separately, dry hop aroma extraction was measured over a short time (1 day) at room temperature in the unhopped beer. Irrespective of the hop form (whole or pellet), the concentrations of hydrocarbon terpenes peaked between 3 and 6 hr and subsequently declined, while the concentrations of terpene alcohols continued to increase throughout the 24 hr dry hop extraction. The rate of hop aroma extraction appeared to be significantly influenced by hop pellet properties and occurred rather rapidly regardless of hop form.

Peter Wolfe received a B.S. degree in physiology from the University of Oregon in 2007. After graduation, he worked as a researcher at the University of Oregon, publishing work on construction ergonomics. He began working toward a master’s degree at Oregon State University in 2010 in the Food Science and Technology Department. Working under Tom Shellhammer, his work focuses on hop aroma in beer and aroma extraction during the dry-hopping process.