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Viscosity & Rheology

Viscosity and rheology are often confused in the literature although they are significantly different concepts. The viscosity of a fluid or suspension is an indication of its fluidity. "Heavy" or "thick" fluids such as heavy oils, or molasses, are recognized as those having high viscosity. Water, many lubricating and cooking oils, coffee, and tea have low viscosities. Air is a fluid with very low viscosity. The rheology of a fluid or suspension, however, is an indication of the behavior of the viscosity as the fluid is sheared (or stirred) at different rates. Whipped cream is easy to stir, but it nevertheless can hold the spoon upright (or at some other odd angle) when not being stirred. This is an example of more complex rheology than simple fluids such as water or oil.

Key analysis

Viscosity

Viscosity changes the flow properties of liquid food and influences the appearance and consistency of a product.

Rheology

Rheology unites the fields of plasticity and non-Newtonian fluid dynamics in static equilibrium.

The typical problem is their failure to discharge reliably from bins, hoppers, silos, feeders, dosing machines, packing machines.

Evaluation of texture involves measuring the response of a food when it is subjected to a force, such as cutting, shearing, chewing, compressing, or stretching. Such tests are essential in the food industry, especially for routine quality control of food products.

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