Systems Analysis of the Plasticization and Extrusion Processing of Mozzarella Cheese

The effect of mixer screw speed and barrel temperature on the length of the filled section in the mixer, melt exit temperature, specific mechanical energy, and viscoelastic properties were determined for low moisture, part-skim Mozzarella cheese. Three vats of cheese were made in 1 d using three different mixer screw speeds (19, 12, and 5 rpm) and three different barrel temperatures (57, 66, and 74°C). For each screw speed (at constant barrel temperature), the horsepower increased almost linearly as the length of the filled section increased. The linearity of the relationship between horsepower and filled length decreased substantially as the barrel temperature (at constant screw speed) increased. The effect of thermomechanical treatment on the rheological properties of the cheeses was determined by plotting the initial modulus in stress relaxation versus cheese exit temperature and specific mechanical energy. This systems approach indicated that the highest moduli were obtained at the highest cheese exit temperatures, which were associated with the lowest specific mechanical energy values. Thus, low shear stresses in the stretcher-cooker seem to promote development of a more extensive elastic network in the cheese.