NOVELTY - Generating biogas, comprises (a) splitting the biomass of an initial substrate in a first fermenter into different intermediate products, (b) catabolizing the intermediate products in a second fermenter to form the biogas, (c) removing one part of the carbon dioxide and hydrogen produced in the first fermenter from the decomposition process during the production of biogas, as a hydrogen-carbon dioxide mixture prior to methanation of the hydrogen-carbon dioxide mixture, and (d) catalytically reacting the mixture in a separate conversion step to form methanol and water or formic acid.    USE - The method is useful for generating biogas in a multi-step decomposition process to form methanol and water or formic acid (claimed).    ADVANTAGE - The method is capable of generating biogas in the multi-step decomposition process with reduced energy consumption to obtain high yield methanol.    DETAILED DESCRIPTION - Generating biogas in a multi-step decomposition process with at least two successively arranged fermenters (1, 2), comprises (a) in a first decomposition step, splitting the biomass of an initial substrate in a first fermenter into different intermediate products such as carbon dioxide, hydrogen, alcohol, acetic acid and other organic acids, (b) catabolizing the intermediate products, in a second decomposition step which is downstream of the first decomposition step, in a second fermenter to form the biogas, (c) removing at least one part of the carbon dioxide and hydrogen produced in the first fermenter as an intermediate product from the decomposition process during the production of biogas, as a hydrogen-carbon dioxide mixture prior to methanation of the hydrogen-carbon dioxide mixture, and (d) catalytically reacting the hydrogen-carbon dioxide mixture in a separate conversion step to form methanol and water or formic acid. An INDEPENDENT CLAIM is included for a plant for generating biogas in a multi-step decomposition process having at least two successively arranged fermenters, each of which is associated with a decomposition step in the production of biogas, where the fermenter which is associated with a first decomposition step, comprises a gas extraction device (5) and that the gas extraction device is connected to a catalytic converter by an extraction line (6).    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a plant for generating biogas in a multi-step decomposition process.    Fermenters (1, 2)    Gas extraction device (5)    Extraction line (6)    Gas storage line (8)    Vacuum generator. (13)