a hogging , sometimes known as reducing , apparatus for reducing wood waste into hog fuel , though some embodiments may also be used for reducing other materials including demolition timber , demolition masonry , mild steel scrap , soft metal scrap , recycled cans , recycled glass , recycled plastic , soft rocks , occasionally hard rocks , recycled roading and asphalt , old tyres , and certain green garden waste . the apparatus includes a drum inclined to the horizontal and into which raw material can be fed at its upper end . rotation of the drum assists driving raw material towards reducing elements positioned at an angle near its lower end . screening apertures allow sufficiently comminuted material to pass therethrough for removal . optional features include internal agitators for improving processing and screening , assisted drying of raw material by motor exhaust , and initial pre - screening of foreign material .