NOVELTY - Producing biogas from a fermentation substrate in at least one fermenter, comprises azeotropically removing a defined partial amount of the fermentation substrate during the dwell time of the fermentation substrate in the fermenter, pumping into a closed circuit through a first heat exchanger (W1), heating, supplying to an additional second heat exchanger (W2), and further heating, where the azeotropically removed fermentation substrate is compressed by the pumping process, and the compressed hot fermentation substrate is pumped into a closed container (B1).    USE - The method is useful for producing biogas from the fermentation substrate.    ADVANTAGE - The method is simple and allows increased production of methane.    DETAILED DESCRIPTION - Producing biogas from a fermentation substrate in at least one fermenter, comprises azeotropically removing a defined partial amount of the fermentation substrate during the dwell time of the fermentation substrate in the fermenter, pumping into a closed circuit through a first heat exchanger (W1), heating to temperatures of up to 110 degrees C, supplying to an additional second heat exchanger (W2), and further heating to a maximum of 180 degrees C, where the azeotropically removed fermentation substrate is compressed by the pumping process at a pressure of 1.5-10, preferably 2-6 bar, and the compressed hot fermentation substrate is pumped into a closed container (B1). The release or maintenance of the pressure takes place in the container, and carbon dioxide, ammonia, traces of hydrogen sulfide and water vapor are released from the fermentation substrate, which are removed as a gas mixture via a exhaust line mounted in the container, and ammonia-reduced fermentation substrate is removed from the container and returned to the fermentation substrate in the fermenter, which is fed for further fermentation. An INDEPENDENT CLAIM is also included for a device for performing the above mentioned method comprising a biogas plant on at least one fermenter, a circuit line, which is connected to the fermentation substrate, a first conduit comprising a pump and connected to a first heat exchanger, which is connected with a second heat exchanger via a second line carrying the fermentation substrate, which is connected with a container via a third line for the separation of ammonia, hydrogen sulfide and water vapor, as exhaust steam. The container is connected with a line discharging the vapors in which a pressure control valve (D1) is incorporated to control the system pressure and a fourth line is provided for discharging ammonia-reduced fermentation substrate, which is connected to a third heat exchanger for cooling the ammonia-reduced fermentation substrate and a fifth conduit leading away from the third heat exchanger is provided for returning ammonia-reduced fermentation substrate into at least one fermenter.    DESCRIPTION OF DRAWING(S) - The figure show a schematic representation of the device for producing biogas.    Container (B1)    Pressure control valve (D1)    First fermenter (F1)    First heat exchanger (W1)    Second heat exchanger (W2)