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During aging and if exposed to oxygen, compounds in hops oxidize into different compounds known collectively as "oxidative polar compounds" or OPC's. Hao et al. (2020) reported 39 different OPC's in aged hops, with 15 of them derived from alpha acids, 15 derived from isomerized alpha acids, and 9 from beta-acids <ref name="Hao_2020" />.  {| class="wikitable sortable"|+ Summary of Oxidized Hop Compounds|-! Oxidized Compound !! Precursor !! Beer Soluble (Y/N) !! Bitterness Level !! Notes|- ||-|}