Screw assembly for cooking extruders operating with significantly reduced specific mechanical energy inputs

A screw assembly for use in a twin-screw cooking extruder and comprising:

• first and second elongated, axially rotatable screws each having an elongated shaft with outwardly extending helical flighting along the length of each shaft, the flighting of each shaft being intermeshed with the flighting of the other shaft,
• said first and second screws being substantially coextensive in length,
• the flighting of each of the first and second shafts presenting a pair of axially spaced apart sections of short pitch length, and an intermediate section having a pitch length greater than the pitch lengths of either of said short pitch length sections,
• said intermediate section having an axial length greater than four times the length of each of said axially spaced apart sections,
• said screws having an SD/RD ratio of from about 1.9-2.5, wherein SD is the outermost screw diameter of the flighting of said first and second shafts, and RD is the root diameter of said first and second shafts.