Arrangement of tight-fitting screw conveyors

An apparatus for processing a foodstuff, the apparatus comprising:

• first and second conveyor screws that are arranged to be rotatably movable relative to each other to process the foodstuff, the first and second conveyor screws including respective helical flights that are interengaged and drivable in opposite relative directions, and the first and second conveyor screws have different outside diameters, a different number of helical flights, or both,
• wherein the helical flights of the first and second conveyor screws each have an outer surface, the outer surfaces being respectively shaped and matched relative to each other, and the outer surfaces being in contact with each other along a substantially continuous contact line extending substantially in a longitudinal direction of the first and second conveyor screws so that a return flow of the foodstuff is hindered.