The use of slit rheometers for on-line viscosity measurements of fluid foodstuffs has been gaining increasing popularity in recent years. However, the viscoelastic nature of fluid foodstuffs necessitates the measurement of their elastic properties, which will provide a better overall understanding of the behavior of the foodstuffs during processing. This review discusses the exit-pressure and hole-pressure methods for the on-line measurement of fluid elasticity, and the application of these methods to the control of the extrusion-cooking process. The potential application of the methods to the rheological characterization of viscoelastic fluid foodstuffs in general is also discussed.
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