TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: The gas mixture leaving the fermenter is fed into the first gas storage unit during a first time period of the rinsing phase. The gas mixture leaving the fermenter is discharged through a biofilter to the environment or burnt by means of a torch during a last time period of the rinsing phase. The formation and energetic recycling of the mixed gas is carried out intermittently. The formation and energetic recycling of the mixed gas is carried out during the biomass exchange (steps ((f) and (a)) determined through a discharge phase and the feeding phase and the first time period (starting fermentation phase) of the subsequent fermentation phase. The second gas storage unit is driven largely empty during the starting fermentation phase. The low methane biogas resulting in a first time period (starting fermentation phase) of the fermentation phase is fed in the second gas storage unit, after closing the feed opening. The phases of the supplying the low methane gas mixture in the second gas storage unit are shorter than the phases of the removing gas from the second gas storage unit for its energy recycling. The methane concentration in the second gas storage unit is constantly maintained above the value of the upper explosive limit in air by supplying the methane-rich biogas. The flowing biomass is methanized under spraying percolate from a percolate fermenter, where the methane-rich biogas fed into the second gas storage unit is removed from the percolate fermenter. The methane-rich biogas leaving the fermenter is temporarily fed into the second gas storage unit, where the supply of methane-rich biogas into the second gas storage unit is carried out before the rinsing phase and/or during the fermentation phase. The second methane-rich biogas fed into the gas storage unit is removed from the first gas storage unit and is supplied via a connecting line of the second gas storage unit interconnecting the two gas storage units. The duration of the rinsing phase is 0.2-1%, preferably 0.3-0.8% of the cycle time. The gas exchange rate during the rinsing of the fermenter with flushing air is 1-10/hour, preferably 2-6/hour, based on the gas volume in the fermenter space. EXAMPLE - No suitable example given.