The Direct Determination of Shear Stress‐Shear Rate Behavior of Foods in the Presence of a Yield Stress

Abstract

SUMMARY The yield stress of food materials plays an important role in their Row characteristics. It is possible to determine the yield stress from the shear stress‐shear rate data determined from a narrow‐gap viscometer and applying Casson's equation. The yield stress determined in this manner checked with the yield stress determined from the torque exerted on a serrated cylinder at rest. However, the yield stress for applesauce and tomato purée is much lower with a single‐cylinder viscometer than with a narrow‐gap viscometer. This is apparently due to disruption of suspension aggregates under shear, with the release of entrapped fluid at the cylinder wall. It is expected that materials in which large amounts of entrapped fluid are released under shear will not exhibit this phenomenon. The shear stress vs. shear rate data from the narrow‐gap viscometer could be fitted by a power‐law equation.