O-2
Bitterness-modifying properties of hop polyphenols extracted from spent hop material
Presenter: Thomas Shellhammer, Oregon State University, Corvallis, OR
Co-Author: Ian McLaughlin, Oregon State University, Corvallis, OR

An aqueous polyphenolic extract was produced from spent Galena hop material and added to a low-bitterness base-beer at three levels (plus 0, plus 100, plus 200 ppm) along with iso-alpha-acids from a preisomerized Galena hop extract at two levels (plus 0, plus 10 ppm) in order to examine the impact on bitterness intensity and character by time-intensity and free-choice profiling methods. Eleven trained panelists evaluated the six sample treatments during two one-week testing sessions, one week for each analysis method. Principal component analysis of the time-intensity results separated the samples with the higher levels of polyphenols and iso-alpha-acids from those with lower levels of both, based on duration, maximum intensity, and area under the curve. Samples 10-100 and 10-200 (10 ppm iso-alpha-acids and 100 or 200 ppm polyphenols added, respectively) were significantly more bitter and had longer bitterness duration than the rest of the samples. Samples with 200 ppm polyphenols added were found to be more bitter than those with only 10 ppm iso-alpha-acids added. The control sample (0-0) fell below all the samples as significantly less bitter. A significant effect was found for both iso-alpha-acids and polyphenols as well as their two-way interaction, for peak intensity and area under the curve (P-value was less than 0.001). Similarly, the results from the free-choice profiling easily separated the extracts by bitterness, lingering bitterness, and astringency. A Tukey's means separation divided each of the six treatments into six distinct groups based on bitterness intensity, into five groups based on bitterness duration (with 10-0 and 0-200 as not different from each other), and into two to three groups based on the remaining consensus descriptors (mouthfeel, astringency, and bitterness come-up time). Samples high in polyphenols were frequently given high intensities for "harsh," "medicinal," and "metallic" descriptors by some panelists. Hop polyphenols contribute substantially to beer bitterness.

Thomas Shellhammer is the Nor'Wester professor of fermentation science and associate professor of brewing and food engineering in the Department of Food Science at Oregon State University. He received his B.S. in fermentation science and Ph.D. in food engineering from the University of California, Davis. He currently serves as member of the ASBC Foundation Board.