Tetrahydro iso-α-acids and hexahydro iso-α-acids are prepared from β-acid resins in the presence of α-acids derivatives without the use of conventional organic solvents. Specifically, the hydrogenation and hydrogenolyzis step is performed using a liquefied hop resin composed of β-acids and α-acid derivatives, hydrogen, and a noble metal hydrogenation catalyst to form desoxytetrahydro α-acids and hydrogenated iso-α-acid derivatives (e. g., tetrahydroiso- and hexahydro iso-α-acids). The desoxytetrahydro α-acids are subsequently auto-oxidized and isomerized by the spent noble metal catalyst in an aqueous alkaline solution (without adding peracids, lead, calcium, or magnesium salts) into the desired tetrahydro iso-α-acids and hexahydro iso-α-acids.
