Cleans and grades semolina in flour and semolina mills. Adjustable product flow is distributed evenly over the screen by a curtain. Sifting uses two or three screen layers. An aerodynamic air channel and adjustable flaps create uniform suction across the screens. Bran and other particles with a large surface area are suspended by suction and directed to the discharge channel. The cleaned semolina is graded by particle size through the screens.