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The impact on analytical and sensory bitterness of hop acids and hop-derived polyphenols resulting from dry-hopping in beer was investigated using a pilot-scale dry-hopping study and a commercial dry-hop survey. The pilot-scale dry-hopping study utilized a trained sensory panel to quantify increases in bitterness caused by dry-hopping an unhopped ale at different dosing rates (0–16 g/L) and exposure times (0–72 h). The International Bitterness Unit (IBU) and a range of hop acids and polyphenols were measured in the dry-hopped beer to determine which specific bitter hop components may have been responsible for dry-hopping bitterness. The commercial survey examined the bitter acids and polyphenol chemistry of 15 different commercial beers, pre- and post-dry-hopped, brewed by Pacific Northwest breweries. Although iso-α-acids (IAA) were the main contributor to beer bitterness, humulinones (oxidized α-acids) and polyphenols were also potentially significant contributors to bitterness, particularly in heavily dry-hopped beer. The increase in beer bitterness (IBU) as a result of dry-hopping was attributed to humulinone extraction and, in some cases, polyphenol extraction. The commercial survey noted a decrease in the total IAA concentrations as a result of dry-hopping in a majority of the samples tested, indicating that the dry-hopping process may remove IAA from beer.
