Abstract: A rotary composter having a rotatably mounted cylindrical vessel divided by baffles into a plurality of compartments, including a first infeed compartment, a last discharge compartment, and a plurality of intermediate digesting compartments. The baffles between the infeed and discharge compartments and the adjacent digesting compartments are configured to retain a supply of microbial inoculant material. A drive mechanism is operable to rotate the vessel at variable speeds to permit the mixing process of material in the vessel to be selectively varied. Air, forced through the vessel from the discharge end to the infeed end, may be preheated prior to introduction into the vessel to assure proper composting during cold weather.