A sieve assembly (100) for a combine harvester includes a frame structure (102). Sieve elements (108) are supported in the frame structure (102). A plurality of pressurized air ports (110) are disposed along the frame structure (102) or sieve elements (108) and are oriented at an angle so as to direct pressurized air upwardly through the sieve elements (108). A pressurized air supply (105) is in communication with the air ports (110).