Mechanisms of fracture in foods

Most foods have solid-like properties and must be size reduced in the mouth before swallowing. What forces and deformations are required to break foods, and how does the mouth achieve them? The fracture processes involved in breaking different food types range widely from brittle fracture in dry cereal foods, nuts and fresh vegetables to the complex defibrillation and tensile failure in cooked meats, and the extreme non-linear behaviour of cheeses. Differences in fracture and failure processes appear to correlate with perceptions of quality in various food types. This allows deduction of an overall model for the mastication process and how consumers may develop preferences for particular foods. The real stresses and strains exerted in the mouth are difficult to identify in local, spacial detail, and frequently more than one food is taken in a single mouthfull. Techniques borrowed from engineering approaches to machine/motion analysis are beginning to define how mouth motion controls the fracture process, mixing and the impact of saliva on the mechanism of swallowing.