NOVELTY - The biogas plant comprises a container in whose interior, biomass such as vegetable residues, liquid manure and/or solid manure is introduced for forming biogas, which is controllably deductible for further use from the container, a carrier (7) projecting in the interior of the container, and a stirring device held at the carrier for mixing the biomass. The container comprises an external wall (13) defining a circumferential direction. The stirring device is arranged in the interior of the container so that a biomass-flow strand of the stirring device is concentrically aligned.    USE - Biogas plant useful for the production of biogas from vegetable residues, liquid manure and/or solid manure.    ADVANTAGE - The biogas plant ensures simple and efficient production of biogas with high yield and high quality.    DETAILED DESCRIPTION - The biogas plant comprises a container in whose interior, biomass such as vegetable residues, liquid manure and/or solid manure is introduced for forming biogas, which is controllably deductible for further use from the container, a carrier (7) projecting in the interior of the container, and a stirring device held at the carrier for mixing the biomass. The container comprises an external wall (13) defining a circumferential direction. The stirring device is arranged in the interior of the container so that a biomass-flow strand of the stirring device is concentrically aligned in external wall circumference of the container in order to produce a running flow of the biomass in the container. The stirring device comprises a propeller axis that is directed tangential to a circumference interior direction concentric to container external wall-circumference direction. The container is rotatably formed and defines a middle point, where the stirring propeller is arranged in interval to middle point and to container-external wall at a circumference direction position in such a way that the propeller axis lies parallel to a bypass to external wall at the same circumference direction position. The carrier is formed through a swivel arm that is pivotably arranged for adjusting the relative height of the stirring device relative to the container base exclusively in a radial plain at the circumferential direction position. A swiveling joint is arranged for the swiveling arm within the container external wall, where the swiveling arm comprises an activation section (8) that extends itself external of the container, and a carrier section (9) that extends itself in the interior of the container and carries the stirring device. The activation section and the carrier section are formed as linear rod section and stand to each other in an obtuse angle of 145 degrees in vertical direction. The carrier has a longitudinal direction in a horizontal- and vertical direction component, where a right angle is adjustable to horizontal direction component. A position arrangement is provided for raising and lowering the stirring device and grips at the activation section of the swiveling arm. The position arrangement is arranged external of the container and comprises electrically operated shaft drives through which the stirring device is adjustable. A control- or regulating device determines a process-optimized immersion depth of the stirring device in the biomass and controls the position arrangement for raising and lowering the stirring device for adjusting the optimum immersion depth. A sensor is provided for determining the immersion depth and delivers an actual immersion-depth signal at the control- and/or regulation device. The sensor is provided for determining the relative height of the stirring device for the container base and delivers an actual-position signal at the control- and/or regulation device. A sensor is provided for determining the filling height of the biomass and delivers a filling height-actual-signal to the control- and/or regulation device, which is arranged external of the container.    DESCRIPTION OF DRAWING(S) - The diagram shows a side view of a carrier present in the container external wall.    Carrier (7)    Activation section (8)    Carrier section (9)    Propeller stirrer (10)    Container external wall. (13)