A combine harvester having a tubular housing that concentrically receives a rotor used for threshing and separating crop materials. Concave assemblies are arranged side-by-side along the a processing system. The processing system also includes at lease one disrupter plate placed between adjacent concave assemblies having an arcuate configuration similar to that of concave assemblies. An upper edge of the disrupter plate projects above the transverse bars and curved rods of the concave assemblies toward the rotor to slow the axial flow of the crop material through the rotor housing. Accordingly, the disrupter plate provides a tortuous flowpath for the crop material as it moves axially through the processing system to permit the more time for threshing and separation to take place.