NOVELTY - The biogas plant-control method includes metering biomass substrate (9) by a substrate metering device (8) and regulating a process parameter as control variable of a fermentation process by a control mechanism with an automatic controller (18). The biogas plant has a fermentation tank (2). A parameter nominal value is assigned to the controller and to which a respectively assigned actual value transmitter (14, 15, 16, 17) is attached.    USE - For the production of fermentation gas.    ADVANTAGE - The biogas plant-control method is cost effective and ensures high yield of fermentation gas.    DETAILED DESCRIPTION - The biogas plant-control method includes metering biomass substrate (9) by a substrate metering device (8) and regulating a process parameter as control variable of a fermentation process by a control mechanism with an automatic controller (18). The biogas plant has a fermentation tank (2). A parameter nominal value is assigned to the controller and to which a respectively assigned actual value transmitter (14, 15, 16, 17) is attached. The transmitter delivers an adjusting signal according to an assignable control algorithm for a subordinate control member of the control system after comparison of the actual value with the nominal value of an observed offset. The offset relative to the process parameter takes place through a control metering of an assigned control biomass, which influences the respective process parameter during the fermentation process. The assigned control biomasses are held back in assigned control storage vessels in liquid and/or granulate-like form and are conveyed by pumps and/or presses and/or worm drive for the control metering. The control biomasses are metered by a control metering device. The influence of assigned control biomasses on the process parameters is stored as program and/or characteristic diagram in a computer. The computer has the function of the automatic controller or assigns the nominal values for a separate automatic controller to a subordinate control metering device. The process parameters obtained by the parameter actual value transmitter are components that are detectable using instrumentation techniques and/or are characteristics of the fermented substrate and/or the produced biogas. The parameter actual value transmitter is made of electrical actual value transmitting transducers that are subordinated to sensors. The control storage vessels are arranged in a battery with a common transport/conveyor-line that is subordinate to the control members that are arranged respectively to the fermentation tank. The control metering takes place directly into the fermentation tank and/or into the substrate metering device as addition to the substrate biomass. A cascade control is intended, in which the regulation of control biomass is assigned as a guidance regulation that is overlaid upon a faster subsequent regulation. A proportional-integral-derivative algorithm is used as control algorithm.    DESCRIPTION OF DRAWING(S) - The drawing shows a biogas plant:    Fermentation tank; (2)    Substrate metering device; (8)    Biomass substrate; (9)    Actual value transmitter; (14, 15, 16, 17)    Automatic controller. (18)