A horizontal grinding machine includes a frame, a feed hopper that receives material to be processed, and a feed conveyor that moves material to be processed in a processing direction. A grinding cylinder rotates about a generally horizontal grinding axis. A feed roller assembly is mounted on the frame at the rear end of the feed hopper and in front of the grinding cylinder. The feed roller assembly includes a feed roller that rotates about a generally horizontal axis in a first direction that urges the material towards the grinding cylinder and a second direction that urges the material away from the grinding cylinder. A controller is operatively connected to the feed roller and to the feed conveyor and controls the rotational speed of the feed roller and the speed of the feed conveyor to obtain a predetermined ratio of feed roller rotational speed to feed conveyor speed.