Mixing, stirring and blending are important processes in industry as well as in the world around us. Whereas fast phenomena such as turbulence provide the unpredictable motion to spread the toxic exhaust gases from cars, the production of the car tyres requires the compounding of very thick and tough materials. The efficiency of the latter may be significantly improved by (slightly) altering the system parameters, such as the position of the exhaust or the geometry of the compounding system. Conditions for proper mixing are formulated and it is investigated if these conditions are met. From this, a procedure for the optimization of mixing of viscous fluids by adjustment of the system parameters is constructed and an optimization of the mixing in our model system is performed.