A sifting apparatus for stratifying raw material includes a material feed-in device, a material support unit, a gas plenum, and a discharge control device. The material support unit receives material from the material feed-in device and has a surface having a plurality of openings for a gaseous medium introduced from underneath the material support unit, thereby effecting loosening and stratification of the material into a layer of relatively heavier material, and a layer of relatively lighter material atop the heavier material. The introduced gaseous medium originates in a pump, is collected in a pressurized reservoir and is controlled by a metered valve prior to introduction to the material support unit.