Involved in the biosynthesis of prenylated phenolics natural products which contribute to the bitter taste of beer and display broad biological activities (Probable). Polyketide synthase that can use 3-methylbutanoyl-CoA (isovaleryl-CoA) and 2-methylpropanoyl-CoA (isobutyryl-CoA) as substrates to produce phlorisovalerophenone (PIVP) and phlorisobutyrophenone (2-methyl-1-(2,4,6-trihydroxyphenyl)propan-1-one), respectively, intermediates in the biosynthesis of the bitter acids (alpha and beta) acids (PubMed:11272819, PubMed:10336650, PubMed:15170123). Can also produce naringenin-chalcone (2',4,4',6'-tetrahydroxychalcone) from 4-coumaroyl-CoA with a lower efficiency (PubMed:15170123). 3-methylbutanoyl-CoA + 3 H(+) + 3 malonyl-CoA = 3 CO2 + 4 CoA + phlorisovalerophenone 4-coumaroyl-CoA + 2 H(+) + 3 malonyl-CoA = 2',4,4',6'-tetrahydroxychalcone + 3 CO2 + 4 CoA 2-methylpropanoyl-CoA + 3 H(+) + 3 malonyl-CoA = 3 CO2 + 4 CoA + phlorisobutanophenone Optimum pH is 7. Secondary metabolite biosynthesis. Homodimer. Expressed in lupulin gland (PubMed:11272819, PubMed:10336650). Present at low levels in leaves but accumulates in cones (PubMed:18519445). Accumulates early in cone development and stays at high levels throughout cone formation. Expression level is directly related with bitter (alpha) acids content, thus influencing the bitter taste of beer, cv. Symphony and cv. Ember having highest levels. Belongs to the thiolase-like superfamily. Chalcone/stilbene synthases family.