Abstract: Tetrahydro iso-?-acids and hexahydro iso-?-acids are prepared from ?-acid resins in the presence of ?-acids derivatives without the use of conventional organic solvents. Specifically, the hydrogenation and hydrogenolyzis step is performed using a liquefied hop resin composed of ?-acids and ?-acid derivatives, hydrogen, and a noble metal hydrogenation catalyst to form desoxytetrahydro ?-acids and hydrogenated iso-?-acid derivatives (e. g., tetrahydroiso- and hexahydro iso-?-acids). The desoxytetrahydro ?-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-?-acids and hexahydro iso-?-acids.