TECHNOLOGY FOCUS - ENVIRONMENT - Preferred Method: The biogas volume, the biogas flow rate, the methane gas content and/or the residual gas content of the produced biogas is determined and is controlled based on the each specific parameter of the fermentable process, where the parameter is preferably used as a control variable. The fermentable process is regulated by controlling at least one operating parameter of solid fermenter, where the operating parameter is preferably used as the control variable. The fermentable process is controlled through the regulation of the temperature in the fermenter over the percolate temperature, the heating temperature of the percolate, the percolation duration, the percolation frequency, the quantity of the applied percolate and/or the pH of the percolate. The residence time of the stackable biomass is regulated in a solid fermenter based on the quality of the produced biogas. The fermentable process is controlled based on the composition, the quantity, the residence time and/or the fermentable state of the biomass present in the solid fermenter, and preferably a reference variable is determined on this basis. The regulation of the fermentable process is carried out separately and independently of the other solid fermenter for each solid fermenter in the biogas plant. At least two solid fermenters are regulated simultaneously based on the amount of the intermixed gas stream of all biogas streams. The percolation duration, the applied percolation amount and/or the percolation frequency are controlled based on the quality of the produced biogas, preferably based on the produced biogas volume, the methane gas content and/or the residual gas content.    TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Components: The device comprises a sensor (80, 82) for determining the quality of the biogas removed from the solid fermenter and a controller (84) for controlling the percolation of solid fermenter. The controller acts on the temperature in the fermenter over the percolate temperature, the heating temperature of the percolate, the percolation duration, the percolation frequency, the amount of the applied percolate and/or the pH of the percolate as the control variable. EXAMPLE - No suitable example given.