A combine harvester includes a grain pan arranged to catch a crop stream, the grain pan being driven in an oscillating manner to convey the crop stream rearwardly to a rear edge. A cleaning unit includes a fan for generating a cleaning airstream which is directed under the rear edge. The grain pan includes a floor profile which defines a transverse profile having ridges and troughs. The troughs provide a plurality of longitudinal channels, wherein the ridge-to-trough height increases in the direction of conveyance. Crop material conveyed by the grain pan experiences channels that deepen towards the rear edge of the pan.
