A concave pan portion of an integral chopper assembly that includes a concave pan shell portion with a separate grate portion that may be easily installed into and removed from an intermediate opening in such concave pan portion for replacement in the event of undesirable wear thereto, and a separate interruption plate installable downstream from the slots in the grate portion for the purpose of effecting a lower mean length of chop (LOC) as the integral chopper assembly operates. The separate grate portion is configured to be installable to fill the intermediate opening in the concave pan shell portion, with a plurality of slots therethrough positioned side by side in the crossways direction to accommodate knife elements that are part of the counter knife assembly.