A rotor for food pulping or straining machines is equipped with a plurality of blades (2) designed to act on the food product to force at least part of it out through a sieve (3) that surrounds the rotor (1) and is characterised in that the blades (2) are shaped in such a way as to cause sudden changes of direction in the moving product particles, thus producing a rapid succession of impulses that act on substantially stationary product particles adhering to the sieve (3), these impulses causing the propulsion of the substantially stationary product particles.