A process is disclosed for producing thermoplastic starch based on renewable raw materials and, if required, for further processing it into a granulate. A low viscosity starch is modified under a low shearing stress during the extrusion process and leaves the extruder with an increased viscosity in the form of a strip, threads or in other geometrical shapes. The advantages of the invention mainly lie in the improved quality of the starch products, the preservation of the mechanical parts of the extruder installation and the increase of the nominal output of the extruder.