Rheology is the study of the relation between forces exerted on a material and ensuring deformation as a function of time.
In the food industry, rheology provides a scientific basis for subjective measurements such as mouthfeel, spreadability and pourability.
It is the study of stress and strain or in other words, it is the study of flow and deformation of materials, both solid and liquid under stress and strain condition.
Primarily rheology deals with three aspects-elasticity, plasticity and viscosity.
ELASTICITY is a property exhibited by solids. It is a characteristic of importance in baked products such as crumb of bread and cake especially when they are fresh. Elastic deformation is reversible. Solid does not flow, however, some solids can be deformed by force and recover when the force is removed. Gels like those of pectin, gelatine and starch are the example of elastic solids. Elasticity can be depicted by spring model, spring clip model and shear pin model.
PLASTICITY-a material that is plastic resists the flow until a force is applied, plastic flow is irreversible. It is exhibited by foods such as cream icing, peanut butter. A plastic food resists changing position until a certain amount of force is applied.
VISCOSITY is a resistance to the flow of a liquid. It is a measure of the resistance of a fluid to deformation under shear stress. It describes a fluid’s internal resistance to flow and maybe thought of as a measure of fluid friction. Thus water is thin having low viscosity while vegetable oil is thick having a high viscosity.