NOVELTY - The method for producing biogas by the fermentation of a fermentation substrate, comprises measuring first, second, third and fourth parameters of the fermentation, comparing the measured value of the first, second, third and fourth parameters with first, second, third and fourth set values assigned the parameters respectively, where the set value defines a value range suitable to maintain the fermentation, and adding reductones to the fermenting substrates, if the measured value of the first, second, third and fourth parameters deviates from the first, second, third and fourth set values.    USE - Method for producing biogas by the fermentation of a fermentation substrate (claimed).    ADVANTAGE - The method ensures cost-effective production of biogas with high quality and quantity and provides increased stability of the fermentation process.    DETAILED DESCRIPTION - The method for producing biogas by the fermentation of a fermentation substrate, comprises measuring first, second, third and fourth parameters of the fermentation, comparing the measured value of the first, second, third and fourth parameters with the first, second, third and fourth set values assigned the parameters respectively, where the set value defines a value range suitable to maintain the fermentation, and adding reductones to the fermenting substrates, if the measured value of the first, second, third and fourth parameters deviates from the first, second, third and fourth set values, or measuring the redox potential of the fermenting substrate, comparing the measured value of the redox potential with a given set value for the redox potential, where the desired value defines a redox potential range suitable to maintain the fermenting process, and adding the reductones to the fermenting substrate, if the measured value of the redox potential deviates from the set value. A range of -450 mV to -530 mV is used as set value for the redox potential. The parameters are quantity of produced biogas, methane content of the produced biogas, hydrogen content of the produced biogas, pH value of the fermenting substrate, redox potential of the fermenting substrate, carbonic acid content of the fermenting substrate, portions of different carbonic acids in the fermenting substrate, hydrogen content of the fermenting substrate, portion of the drying substance of the fermenting substrate, portion of the organic drying substance of the fermenting substrate, viscosity of the fermenting substrate and space load of the fermentation reactor. A redox-active substance is added to the fermenting substrate and is a reducing agent. An organic or inorganic oxidation agent is used as redox-active substance. The reductone is added in a concentration of 0.5-0.1 g/l to the fermenting substrate. The fermentation is carried out in a fermentation reactor and the space load is continuously increased in the fermenting reactor by continuous supply of fermenting substrate. The production of biogas is carried out through fermentation of fermenting substrate in a space load of greater than or equal to 8.0 kg oTS/m3d at 40-50 degrees C under constant through mixing of the fermenting substrate. A range of 5-8.5 is used as set value for pH value of the fermenting substrate. A type of microorganism is additionally added to the fermenting substrate. The fermenting substrate is continuously added and the redox potential of the fermenting substrate is continuously measured. An experimental fermentation of the fermenting substrate is additionally carried out for the production of biogas. The redox potential of the fermenting substrate is repeatedly measured and the redox potential range suitable for the maintenance of the production of the biogas is determined from the measured value. An INDEPENDENT CLAIM is included for a fermenter for biogas production.    DESCRIPTION OF DRAWING(S) - The figure shows a graph, in which the quantity of produced fermentation gas and/or the space load of the fermenter are plotted against the time (Drawing includes non-English language text).