The biomass, such as solid manure, straw or silage, is fed into the machine from above, pre-shredded by a ripping comb above the rotor and then enters the impact zone. Shredding then takes place by means of a rapidly rotating rotor and impact bars made of wear-resistant material. The beaters mounted on the rotor provide a blunt de-fibering action, resulting in a homogeneous and well-digested substrate that is ideally prepared for anaerobic digestion.