Abstract: Apparatus for preparing stable humus from a batch of organic waste material. The apparatus has an elongated drum-like reactor vessel and a prime mover operatively connected thereto to rotate the reactor vessel about its axis. At least one non-rotating sensor wand within the reactor vessel for sensing temperature and collecting gas samples within and substantially across the volume of the reactor vessel and within and substantially across the volume of the waste material. The sensor wand is connected to a gas analyzer and a temperature monitor. The reactor vessel has affixed to its inside surface a longitudinal manifold, with pairs of aeration pipes extending to other side thereof and evenly spaced therealong. A variable speed blower has an outlet operatively connected to the manifold. A process control computer has inputs from the gas analyzer and the temperature monitor and outputs to control the prime mover and the variable speed blower.