The impact of the modification of the plasticizing system of the TS-45 single-screw extruder (by ZMCh Metalchem, Gliwice, Poland) with L/D = 12 is discussed in the article. The modification involved the reconfiguration of the extruder screw to achieve certain selected physical characteristics of the lignocellulosic raw materials which are not commonly used in biogas facilities. Shredded lignocellulosic raw materials (corn straw, wheat straw, and hay) were moistened to achieve a 25% water content and extruded at three rotational speeds of the extruder screw: 70, 90, and 110 rpm. During extrusion-cooking, the process efficiency and energy intensity were determined. The obtained extrudates were studied in order to establish selected physical properties (water solubility index, water absorption index and bulk density). In addition, the research included an analysis of microscopic images and the efficiency of cumulative methane and biogas production per fresh mass, dry mass, and dry organic mass. In addition, an analysis of the FTIR infrared spectra of the studied extruded samples was performed, these contained lignocellulose structures, and revealed explicit changes at the molecular level. The use of the extrusion technique as a pretreatment of the plant biomass allowed for the lignocellulosic bonds to be broken, which loosened the structure of the material and thus changed its physical properties and biogas efficiency.