Cheese: Structure, Rheology and Texture

Abstract

The rheology of cheese characterizes its deformation behaviour when subjected to stress or strain. Based on stress/strain behaviour, materials may be generally classified as ideal elastic solids, ideal viscous (Newtonian) liquids, or viscoelastic. Cheeses, like most other solid- and semi-solid foods that contain moisture and solids such as protein, fat and/or carbohydrate, exhibit the characteristics of both an elastic solid and a viscous fluid, and are thus termed viscoelastic. The rheological behaviour of cheese can be measured by an array of tests. Some tests, for example creep and low strain oscillation rheometry, involve application of a low strain (e.g., <0.05) within the linear viscoelastic range, the region where stress in the sample is directly proportional to the applied strain and the sample, like an elastic solid, recovers fully from the deformation on removal of the strain (at least after short time scales). Low strain rheology tests give information on fundamental intrinsic rheological quantities such as storage modulus, G′, and elastic creep compliance. These tests are useful also for characterizing the viscoelasticity of cheese, in terms of how close it behaves to a solid or a liquid. In other tests such as large strain compression, large strain torsion and cutting tests, the cheese is subjected to a large strain (e.g. ≫0.5) outside the viscoelastic range. The strains applied in these tests simulate more closely those applied during consumption and commercial size-reduction operations, which include portioning/cutting, shredding or grinding of cheese. Large strain deformation provides information on the fracture properties of the cheese, including the stress required to fracture, the strain at fracture, and the stress required to achieve a given degree of deformation, such as compression.