Abstract: A digester is disclosed for controlling the decomposition of organic matter to produce a useful gas and a liquid fertilizer. The digester comprises three slurry chambers connected in tandem by passthrough tubes. A fourth chamber used for gas collection is located above the three slurry chambers. An input line is connected to the bottom of the first chamber and an output line is connected to the bottom of an upright tube provided in the third chamber. A slurry containing raw manure or other organic waste is loaded from a mix tank through the input line to fill the three chambers to a level determined by the top of the upright tube in the third chamber. The process of aerobic digestion and a limited form of anaerobic digestion is carried out in the first chamber and the process of anaerobic digestion which produces the methane gas is carried out in the second chamber which is heated.