ABSTRACT
This chapter covers the fundamentals of rheology as they pertain to low and intermediate moisture food doughs. In extrusion, the behavior of the fluid food dough under the influence of a shearing stress is of primary interest. Several types of non-Newtonian viscous behaviors have been recognized. The existence of an apparent Newtonian shear stress-shear rate relationship for pseudoplastics at very low and high γ has been attributed to the nature of the molecules in the food doughs. The effect of moisture content and temperature has been included in models for apparent viscosity. The measurement techniques used to determine the rheological properties of food doughs have been reviewed by J. P. Clark. The rheological behavior of a fluid profoundly influences the shape of the velocity profile which results as the fluid flows through some type of conduit. Torque rheometers have been used to study the rheological behavior of food systems.
