Influences of Hop Components on Beer Quality

Dr. Thomas H. Shellhammer, Nor'Wester Professor of Fermentation Science, Associate Professor of Brewing and Food Engineering, Department of Food Science and Technology, Oregon State University, Corvallis, Oregon

Hops play a significant role in beer flavor and quality. Work funded by the HRC in Dr. Shellhammer’s lab focuses on hop components that influence the bitterness quality of beer as well has beer shelf life. The quality of hop bitterness is a subtle but powerful driver of beer quality and contributes significantly to the “drinkability” of the final product.

Bitterness in beer is derived primarily from alpha acid isomerization, which occurs during wort boiling. The alpha acids represent a group of chemically similar compounds, the proportions of which vary greatly depending upon variety. The cohumulone content is varietal dependent and it is often used as a quality index in the selection of existing and new hop varieties. A direct relationship between alpha acid composition and bitter quality is speculative, and anecdotal reports indicate that varieties high in cohumulone lead to an inferior bitter quality in the finished beer. Despite the paucity of scientific evidence, cohumulone levels are still used an index for hop quality. Dr. Shellhammer’s lab has examined the influence of cohumulone level on beer bitterness quality and discovered that this factor has relatively minimal impact on bitter quality.

The influence of hop polyphenol on hop bitter intensity, bitter quality (harshness versus smoothness) and tannin astringency is also being explored by Dr. Shellhammer. In other food systems, monomers and polymers of flavanols elicit bitterness and astringency depending upon their degree of polymerization yet the sensorial effect of these compounds in beer has not been adequately determined. Dr. Shellhammer has investigated bitter quality in addition to temporal bitter parameters (intensity, duration, etc) of hop-derived polyphenols in beer and discovered that these compounds contribute significantly to beer bitterness and the quality of bitter from hop polyphenols may be varietal-dependent.

Due to their antioxidant power, hop polyphenols may also contribute positively to beer flavor stability. While the majority of the polyphenolic content of beer comes from malt, hop polyphenols contribute up to one third of the total phenolic load in beer and therefore cannot be ignored in regard to their effect on flavor stability and quality. Dr. Shellhammer’s lab has demonstrated the positive dose-response behavior of added hop polyphenols toward improving the antioxidant power of beer. This work will continue to investigate the influence of hop polyphenols on beer flavor stability.