The rheological and mechanical properties of fat materials arise directly from their composition and how these components are structurally organized. In turn, the structure is markedly dependent on the various heat and momentum transfer processes that take place in the various unit operations employed in the manufacture of the fat material. The rheological properties displayed by a given fat system depend strongly on the physical state of the material. The biphasic nature (liquid and solid) of a fat system in large measure governs product structure, and as a consequence it governs fat rheology. the degree of solidity of the fat can be strongly temperature dependent; therefore, temperature has a pronounced effect on the rheological response of fat. Mechanical performance during processing is an essential quality feature when fats are used as ingredients in food. In addition, fats confer desirable mouthfeel characteristics such as smoothness and creaminess, and these sensory properties are largely determined by flow of the material to form thin layers in the oral cavity. As a result, many food processors stipulate that some assessment of the rheological properties of fats be conducted as a quality control.