Bitterness Intensity of Oxidized Hop Acids: Humulinones and Hulupones

Humulinone and hulupone extracts were prepared for evaluating their bitterness intensity in beer. Previously established methods for oxidizing alpha- and beta-acids followed by preparative liquid chromatography resulted in humulinone and hulupone extracts of 93.5 and 92.7% purity, respectively, as measured by HPLC. The humulinone and hulupone extracts were dosed into unhopped lager over a range of concentrations from 8 to 40 mg/L. Similarly, purified iso-alpha-acids were dosed into unhopped beer at concentrations ranging from 6 to 30 mg/L. A nine-member trained panel scaled the bitterness intensity of all samples in five replicated testing sessions. Humulinones were found to be 66% as bitter as iso-alpha-acids (+/- 13%), and hulupones were found to be 84% as bitter as iso-alpha-acids (+/- 10%). The results of this study suggest that humulinones and hulupones are more bitter than was previously suspected.