TECHNOLOGY FOCUS - BIOLOGY - Preferred Method: The method is operated continuously or batchwise. The step of circulating the mixture of horse manure and aqueous medium and the step of homogenizing the horse manure in the aqueous medium are effected by introducing the gaseous medium in the mixture of horse manure and aqueous medium. The skimmed and crushed straw is fermented together with the pretreated horse manure. Preferred Components: The horse manure is combined with an amount of aqueous medium to the mixture, which comprises a dry substance content of less than or equal to 15% preferably 9% or 8% after homogenization. The litter comprises straw long straw, and the skimmed straw is crushed to a stem length of less than or equal to 10 mm. The horse manure contains impurities such as sand and stones, where the impurities are separated from the mixture of horse manure and aqueous medium due to density and/or inertia differences.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The gaseous medium is compressed air.    TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Components: The gassing device is arranged for introducing the gaseous medium such that the introduction of the gaseous medium produces a circulation of the aqueous medium present in the container. The litter-skimming device is constructed as a rake, and a bar screen with rotating cleaning rakes. The container is subdivided in the three portions in a flow direction of the mixture of horse manure and aqueous medium, where: the first container portion comprises a device for feeding the for horse manure and the aqueous medium; the second container portion includes the litter-skimming device in the flow direction of the first container portion; the third container portion includes the groove in the flow direction of the second container portion; and the gassing device extends over the container portions. The gassing device is arranged with respect to a center of the groove to the container side with the litter-skimming device towards the top of the groove or in a transition region between the groove and an overlying container part.