ABSTRACT
Viscosity data must be expressed in fundamental units that are obtainable with well-designed viscometers. By changing the shear rate and measuring the resulting shear stress, it is possible to obtain viscosity measurements over a wide range of shearing conditions. In pseudoplastic flow, the curve begins at the origin of the shear stress-shear rate plot but is concave upwards; i.e., an increasing shear stress gives a more than proportional increase in shear rate. Foods that exhibit time-dependent shear-thinning behavior are said to exhibit thixotropic flow behavior. Time-dependent shear-thickening behavior is called rheopectic behavior. The shear stress magnitudes that need to be measured are low for foods with low viscosity. If the flow properties of the food are needed to design for processing operations, it is necessary to use shear rates that span the range expected to be used in the process.
