Filled snack production by coextrusion-cooking: 1. Rheological modelling of the process

Filled snack production has been considered and modelled by considering the rheological properties of the different components. The possibility of inserting the filler directly inside the extruder head allows post-extrusion swelling to decrease thus increasing the product quality. To find the optimum position of the filler nozzle with respect to the head extruder orifice, a rheological model was developed by assuming power law behaviour for both dough and filler tangential stresses and a single relaxation time mechanism for the normal stresses shown by dough. The internal swelling was computed numerically for typical industrial conditions and a validation of the model was done by varying around the mass flow rate of dough, the flow indexes of the two components, the consistency index of dough, and finally some geometrical conditions. It was found that the system did not depend too much on the geometry, but is very sensitive to dough and filler rheological properties. The simulation predictions appeared to be in agreement with industrial expectations, predicting a short distance between nozzle and extruder head.