Q. Explain about Rheology of Foods?

Rheology is the study of stress and strain or in other words, it is the study of flow and deformation of materials, both liquids and solids, under stress and strain conditions. Primarily, rheology deals with three aspects -Elasticity, Plasticity and Viscosity.

The flow characteristics of a food are actually quite complex. For example, if bread dough is stretched, but not too far, it will spring back; to the extent that it does, the dough is elastic. Elasticity is a characteristic of importance in baked products too. Such as crumb of bread and cake, especially so when they are fresh.

Elastic deformation is reversible but plastic is not. A material that exhibits plastic flow resists changing position until a minimum force is applied. This is a desirable characteristic in cake frosting. A soft frosting is desired, but it should stay in place but not flow down the sides of the cake.

Solids do not flow; however, some solids can be deformed by force and recover when the force is removed. This is elasticity and gels like those of pectin, gelatin and starch baked custard etc. are examples of elastic solids. There a number of objectives tests to determine the firmness of gels. A material that is plastic resists flow until a force is applied but unlike elastic flow, plastic flow is irreversible.