The mixture of corn semolina with oat components was extruded in a single screw extrusion-cooker S-45 (L : D = 12 : 1, compression ratio of 3 : 1) and twin screw extrusion-cooker 2S-9/5. The purpose of the research was to estimate the influence of the moisture content of raw material, mixture component and the process temperature on the viscosity of grounded extrudate slurries in distilled water. With the process parameters and material properties assumed for this study, it was possible to obtain stable working conditions for the single screw extrusion-cooker when the share of oat component in the mixture was up to 21%. For twin screw extrusion-cooker share of oat component was up to 80%. It was observed that process temperature and mixture component has the highest influence of viscosity, whilst moisture content has a small influence on the viscosity.