NOVELTY - The method comprises feeding a substrate to a container (1) using a delivery system, arranging two stirrers (2) into the container, where a propeller (3) of the stirrers are rotatably displaced over a drive, producing horizontal flows of the contents of the container by the propeller, selecting the propeller diameter, propeller geometry and position of the propeller, so that a common mixing zone of the fermentation substrate is producible in the container, and detecting the measurement data for determining the average speed and/or the average viscosity of the substrate in the mixing zone.    USE - Method for producing biogas from organic materials.    ADVANTAGE - The method ensures economical and efficient production of the biogas with high yield and less energy consumption.    DETAILED DESCRIPTION - The method comprises feeding a substrate to a container (1) using a delivery system, arranging two stirrers (2) into the container, where a propeller (3) of the stirrers are rotatably displaced over a drive, producing horizontal flows of the contents of the container by the propeller, selecting the propeller diameter, the propeller geometry and the position of the propeller, so that a common mixing zone of the fermentation substrate is producible in the container, detecting the measurement data for determining the average speed and/or the average viscosity of the fermentation substrate in the mixing zone, leading back the measurement data to a regulating unit, and varying the control variables by the regulating unit, where the control variables change the power input of the stirrers in the mixing zone and/or the composition and/or the flow characteristics of the container contents. The regulating unit varies the number of rotations of one of the stirrers as control variable, and switches an additional stirrer. The regulating unit varies the quantity, the composition of the fed substrate and/or recirculates and/or biochemically or physically varies the flow characteristics of the fermentation substrate. The average speed in the mixing zone is detected by an ultrasound probe. The measurement data are detected for determining the viscosity over the power consumption of the stirrers, and are detected for determining the flow characteristics over the power consumption of the stirrers. A direct or indirect power determination from the stirrers takes place on the basis of electrical or mechanical measurement data. The measurement data are detected for determining the viscosities with a viscometer. A ratio of the height to largest diameter of the container is less than 0.5. An INDEPENDENT CLAIM is included for a device for producing biogas from organic materials.    DESCRIPTION OF DRAWING(S) - The figure shows a perspective view of a container for biogas production with two main stirrers.    Container (1)    Stirrers (2)    Propeller. (3)