Abstract: A combine cleaning system including a fan and a cleaning sieve which coact with each other to separate chaff and unthreshed tailings from grain. The sieve defines a grain cleaning area comprised of an air foil section extending rearwardly from a forward edge of the sieve and a slat or louvered section downstream of the air foil section. The air foil section provides a first level of cleaning to the threshed materials deposited on the grain cleaning area while the slat section provides a second level of cleaning to the material received thereon. Preferably, the air foil section comprises about 60% to about 85% of the grain cleaning area.