NOVELTY - Two- or multistage biogas production by hydrolysis of solid biogenic substances in percolators, comprises: a hydrolysis step comprising hydrolyzing the biogenic substances, which forms liquid hydrolyzate and hydrolysis gas in the percolator, and removing and collecting the hydrolyzate from the percolators; and a methane step comprising converting the hydrolyzate into biogas and fermentation liquid by methane producing microorganisms, and removing and collecting the fermenting liquid from the methane reactor and optionally feeding it to the hydrolysis step.    USE - The carbon dioxide rich hydrolysis gas obtained during the biogas production is useful for flushing the reactors of the single stage biogas plants (claimed).    ADVANTAGE - The method: makes use of gas-tight percolators and thus results in a better conversion of the biogenic materials to energetically usable biogas; reduces the conversion of biogenic materials into energetically unfavorable carbon dioxide and water; produces the biogas with high methane content as compared to the conventional single- and two-step biogas production process; and exhibits a safe and environmentally friendly operation of the biogas plant.    DETAILED DESCRIPTION - Two- or multistage biogas production by hydrolysis of solid biogenic substances in percolators, comprises: a hydrolysis step comprising hydrolyzing the biogenic substances, which forms liquid hydrolyzate and hydrolysis gas in the percolator, where carbon dioxide rich hydrolysis gas is formed initially and subsequently methane containing hydrolysis gas is formed, and removing and collecting the hydrolyzate from the percolators, where one portion of the hydrolyzate is fed to the methane step and the other portion of the hydrolyzate is fed to the hydrolysis step; and a methane step comprising converting the hydrolyzate into biogas and fermentation liquid by methane producing microorganisms, and removing and collecting the fermenting liquid from the methane reactor and optionally feeding it to the hydrolysis step. The percolators operate gas-tight and hydrolysis gas is discharged from the percolators, where methane containing hydrolysis gas is fed for energetic utilization and the carbon dioxide rich hydrolysis gas discharged from the percolator is either unused or is fed to a process-technical utilization. An INDEPENDENT CLAIM is also included for a plant for two- or multistage biogas production, comprising at least one percolator, preferably a solid percolator exhibiting a hydrolyzate discharge and a liquid feed line, where the hydrolyzate discharge is connected with a methane reactor by at least one hydrolyzate storage tank, and the methane reactor is downstream to at least one fermentation liquid storage tank above a fermentation liquid discharge. The hydrolyzate storage tank and fermentation liquid storage tank are connected with the liquid feed line of the percolator. The percolator is designed gas-tight and comprises at least one sealable gas feed line and gas discharge, respectively. The percolator is connected with a methane sensor, which is used for determining the methane content of the gas present in the percolator, and with a pH sensor, which is used for determining the pH of the liquid present in the percolator. The gas feed line of the percolator is designed such that switching of air supply, switching of inert gas supply or closure of the gas feed line is possible.