NOVELTY - The method for producing biogas in a fermentation reactor using microorganisms, comprises determining a first, second, third, fourth and fifth target value range associated respectively with a first, second, third, fourth and fifth characteristic parameter of the fermentation, determining measurement values of the first, second, third, fourth and fifth characteristic parameters during the fermentation process, comparing the measured values of the characteristic parameter respectively to the target value range, and adding one type of microorganisms to the fermentation substrate.    USE - Method for producing biogas in a fermentation reactor using microorganisms.    ADVANTAGE - The method ensures cost-effective production of biogas and provides increased stability of the fermentation process.    DETAILED DESCRIPTION - The method for producing biogas in a fermentation reactor using microorganisms, comprises determining a first, second, third, fourth and fifth target value range associated respectively with a first, second, third, fourth and fifth characteristic parameter of the fermentation, where the first, second, third, fourth and fifth target value range respectively defines a first, second, third, fourth and fifth value range suitable for maintaining the fermentation, determining measurement values of the first, second, third, fourth and fifth characteristic parameters during the fermentation process, comparing the measured values of the first, second, third, fourth and fifth characteristic parameter respectively to the first, second, third, fourth and fifth target value range, and adding one type of microorganisms to the fermentation substrate if the measured value of the first, second, third, fourth and fifth characteristic parameter has a respectively defined relation to the first, second, third, fourth and fifth target value range. The characteristic parameters of the fermentation 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. The microorganisms are: two members of hydrolytically active fermentation microorganism, acidogenic fermentation microorganisms, methanogenic fermentation microorganisms and acetogenic fermentation microorganisms; three members of hydrolytically active fermentation microorganism, acidogenic fermentation microorganisms, methanogenic fermentation microorganisms and acetogenic fermentation microorganisms; and one type of hydrolytically active fermentation microorganism, one type of acidogenic fermentation microorganisms, one type of acetogenic fermentation microorganisms and one type of methanogenic fermentation microorganisms. The individual types of microorganisms are added in the form of microorganism cultures, where the cultures of microorganisms consist of a kind of microorganisms. A pure culture of microorganisms is added. A fixed set value range represents a value ranges of the first derivative of the measured variable after the time of the characteristic parameter and the specified relation of the measured values of the characteristic parameter is assigned to the set value range assigned to the parameter so that the first derivative of the measured values lies outside of the fixed set value range. A fixed set value range represents a value ranges of the second derivative of the measured variable after the time of the characteristic parameter and the specified relation of the measured values of the characteristic parameter is assigned to the set value range assigned to the parameter so that the second derivative of the measured values lies outside of the fixed set value range. Additional biomass is introduced into the fermentation reactor for the addition of the microorganisms. The space load is continuously increased in the fermentation reactor through continuous addition of biomass. The biogas production is carried out with the space load of greater than or equal to 8 kg oTS/m3d under constant mixing of the fermenting substrate at 40-50 degrees C. A range of 5-8.5 is used as set value range for the pH value. A range of -450 mV to -530 mV is used as set value range for the redox potential. The fermentation substrate is continuously added and the parameters of the fermentation are continuously measured. An experimental fermentation of the fermentation substrate is additionally carried out for the production of biogas, where the characteristic parameters of the fermentation are measured several times and are determined from the measured values of the set value range suitable for the maintenance of the production of biogas. A type of microorganisms is added in a quantity to the fermentation substrate. The portion of the added kind of microorganisms is 10-3 to 1% of the total number of microorganisms present in the fermentation substrate.    DESCRIPTION OF DRAWING(S) - The diagram shows a graph, in which the quantity of produced fermentation gas and the space load of the fermenter are plotted against the time (Drawing includes non-English language text).