Abstract: The apparatus for trimming a layer of back fat off a pork shoulder butt comprises a frame as well as a flat, flexible and arcuate cutting blade with two ends respectively attached to a pair of blade holders pivotally mounted onto the frame. A conveyor, a set of upper gripper belts, and a rotative roller pass the shoulder butt through the blade to trim off the layer of fat. The rotative roller has a diameter gradually decreasing along its longitudinal axis from each end of the roller toward the center thereof to define an annular, concave outer surface. This roller is mounted onto the frame adjacent the arcuate blade on the outside of the curve this blade defines but with a distance separating the annular surface and the blade to enable passage of the layer of fat between them. The annular outer surface of the roller is formed with teeth to engage the fat whereby rotation of the roller forces the shoulder butt through the blade.