Abstract: A composting machine is used with an elongated reactor with flails mounted in a frame that moves longitudinally from a finishing end to a starting end during a processing pass. The flails move the organic material in the reactor along the reactor toward the finishing end. The flails are radially mounted on a shaft and the shaft rotates during the processing pass causing the flails to rotate as well. During a return pass, the flails can be made to occupy a horizontal plane so that the frame can return to the finishing end without raising the shaft vertically. Further, a skirt can be mounted adjacent to the flails to limit the distance that the material is moved by the flails. The distance of the skirt from a leading edge of the flails can be increased during the processing pass from the finishing end to the starting end. This allows the machine to be much more efficient as the level of the organic material can be maintained nearly constant from the starting end to the finishing end.