An assembly of 4 to 8 metal trays, usually 30 in (76.2 cm) wide and 8 to 15 in (20.3 to 38.1 cm) long, arranged in series in the direction of flow. The trays are detachably mounted in the assembly by steps, so that the overflow from one tray overlaps the next tray by 1 in (2.54 cm) and is 2 to 4 in (5.1 to 10.2 cm) above it. The trays are inclined downward in the direction of the flow at an angle adjustable from 14 degrees to 18 degrees. The entire assembly is mechanically oscillated transversely to the direction of the flow at about 200 strokes/min with an adjustable stroke of about 1/2 in (1.27 cm). The storage bin and feed roller are independently mounted and discharge a layer 1 grain thick.