Abstract: Organic material and animal excrement is fermented in an accelerated manner in closed systems in order to produce energy, such as biogas and heat, wherein, as a rule, the material is moved around or constantly shifted, respectively, in known devices. According to the invention, the material to be fermented, organic waste and excrement, preferably from large-scale animal maintenance, is brought together and fed to inclined shafts from above, wherein it sinks down by means of its own force of gravity and is mixed at intervals by means of a mixing angle attached at a chain hoist. The inclined bottoms of the shafts form the heat exchanger units, for which purpose the outer defining walls can also be used. The entire system is completely insulated and can be coated automatically from above.