Dry hopping low IBU beers and its effect on beer bitterness

Low IBU beers (20 ppm of isoalpha acids or less) that are heavily dry hopped, with 1 lb of hops per barrel (0,381 kg/hl) or more, can experience signiἀcant changes in hop acid composition.

Unlike high IBU beers, low IBU beers that are dry hopped loose very little isoalpha acids yet gain significant amounts of humulinones and alpha acids. Humulinones are reported to be 66% as bitter as isoalpha acids and alpha acids about 1/10th as bitter as isoalpha acids. The below table contains the HPLC analysis of a control beer dry hopped with 0.5 lbs, 1.0 lbs, and 2.0 lbs of Cascade hop pellets for three days at 16 °C. The Cascade hops assayed 0.26% humulinone and 5.6% alpha acids.

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