Screw assemblies are provided for cooking extruders characterized by operation using significantly reduced specific mechanical energy inputs, wherein the screw assemblies include first and second elongated, axially rotatable screws which are substantially coextensive in length, with the screw flighting presenting a pair of axially spaced apart sections of short pitch length and an intermediate section of greater pitch length. The intermediate section has an axial length greater than about four times the length of the axially spaced apart sections. The screw assemblies permit incorporation of significantly greater amounts of steam into comestible products during cooking thereof, as compared with prior art designs.