The stimulus associated with oral evaluation of the viscosity of liquid and viscous foods appears to embrace a range of shear rates extending from 10-l to lo00 s-1. The value associated with a particular food depends on its flow characteristics. For liquid foods the stimulus appears to be the shear rate developed at an approximately constant shear stress (-100 dyn cm-2), whereas for viscous foods it appears to be the shear stress developed at an approximately constant shear rate (-10 s-1). Additional factors may be involved when evaluating highly viscous non-Newtonian foods or foods with an oil continuous medium. These are 'plug flow' or the spreading coefficient.respectively.

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Abstract. Analysis of published chewing force patterns indicates that the ‘first bite’ involves an approximately linear application of force. The Instron Universal Testing Machine also offers a linear pattern of force application making it possible to obtain information about textural properties identified during the ‘first bite’ from force‐compression tests. However, the data obtained in such tests are influenced not only by the applied force but also by the rate at which it is applied. Both variables must be taken into account when analysing the data, since the applied force in chewing and also the rate of force application depend on the textural characteristics of the food being evaluated. Based on a correlation of sensory responses with instrumental force‐compression‐rate of force application data, a procedure is described for establishing the mechanical force conditions that should be used in Instron tests so that they simulate those associated with the sensory evaluation.

Cheese maturity, test temperature, crosshead speed, sample shape, sample height and surface area influence the force‐compression behaviour of Gouda cheese in an Instron Universal Testing Machine. Introducing mineral oil or Emery paper between the sample's surfaces and the compression plates affects the shape of the compressed samples. Cine‐film records indicate that deformation is barrel‐shaped (convex) with Emery paper and under normal test conditions, and concave with mineral oil. In the first two test situations friction prevents the cheese surfaces from spreading to the same extent during sample compression as when using mineral oil. Compression as modified by friction may be the principal factor associated with the subjective evaluation of firmness by squeezing samples between the fingers. Firmness evaluation by chewing involves still higher percent compressions which, in Instron tests, lead to sample breakdown and crack propagation.