For feeding biogas plants, with robust technology, inexpensive material such as manure, grass and silage is used. These naturally contain large amounts of fibre, which not only place high demands on the technology, but also on the biology. These raw fibres in the substrate are very difficult for the bacteria in the fermenter to "digest". In our heat technology Heatcrack the unprocessed raw fibre components are thermally processed and can then be better utilised by the bacteria. Excellent results were achieved in the "heat technology trials" carried out by our research laboratory: Up to approx. 5% more biogas yield can be achieved in practice by using the substrate digestion system.