NOVELTY - The method for mechanical processing of a biomass grinding product as starting substrate (1) to form a product substrate (1') in a fermenter of a biogas plant, comprises supplying a process liquid (2) such as water to the starting substrate to promote the mechanical or the mechanical and a biochemical conditioning process, and then receiving the product substrate, which allows the production of a biogas quantity by mechanical conditioning, during the fermentation processes with comparable starting substrate quantity and by mechanical and biochemical conditioning.    USE - Method for mechanical processing of a biomass grinding product as starting substrate to form a product substrate in a fermenter of a biogas plant, where the product substrate produces biogas.    ADVANTAGE - The method is capable of mechanical processing of a biomass grinding product to form a product substrate with high degree of gloss, increased wetting capability and reduced floating layer formation, thus providing an effective, biochemical metabolism of the product substrate, which permits generation of increased biogas quantity, predetermined energy conservation and increased organic load.    DETAILED DESCRIPTION - The method for mechanical processing of a biomass grinding product as starting substrate (1) to form a product substrate (1') in a fermenter of a biogas plant, comprises supplying a process liquid (2) such as water to the starting substrate to promote the mechanical or the mechanical and a biochemical conditioning process, and then receiving the product substrate, which allows the production of a biogas quantity by mechanical conditioning, during the fermentation processes with comparable starting substrate quantity and by mechanical and biochemical conditioning. A forced wet grinding is carried out with the starting substrate by the mechanical processing and the supply of process liquid. The process liquid is formed from water and biochemically active ingredients, anaerobic bacteria strains and/or biochemical enzymes as catalysts in the form of additives. A recirculated product from the fermentation process is used as the additive. The starting substrate is subjected or mechanically cut in an impact crusher. A predetermined particle size and/or a predetermined fiber length of the product substrate is adjusted by changing a peripheral speed, rotation of milling/cutting tools and throughput of the starting substrate and/or in dependence of the kind of filter and filter punching of a perforated basket (112) of an impact crushing mill (100). The product substrate is produced with a small particle size and/or a shortened fiber length by the impact crusher so that a larger specific surface of the product substrate is reached and the biochemical metabolism is stimulated in the fermentation process. The starting substrate and the product substrate are mechanically lockable with substrate particles of 25% smaller than 4 mm and with substrate particles of 90% smaller 4 mm respectively. A homogenization of the particle size of the product substrate and a laminar application of force on the particles and/or fibers of the starting substrate are reached by the impact crusher, where the fluidity of the product substrate is increased and/or its viscosity is decreased. The supply of process liquid is varied depending upon the ratio of the quantity of the starting substrate to the process liquid and is adjusted from a largest concentration, where the drying substance of the starting substrate in relation to the process liquid is 60:40 to a smallest concentration, where the drying substance of the starting substrate in relation to the process liquid is 10:90. The ingredients, anaerobic bacteria strains and/or enzymes have a dry substance concentration of 0-10%. The temperature for the process liquid is 5-70 degrees C. An INDEPENDENT CLAIM is included for an impact crushing mill.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic representation of an impact crushing mill.    Starting substrate (1)    Product substrate (1')    Process liquid (2)    Impact crushing mill (100)    Perforated basket. (112)