Brittle textures in processed foods

Summary

Processes and products

Brittle products are associated with a wide range of raw materials. In the confectionery area chocolate, toffee and boiled sweets are products which may break at low strains under certain conditions of composition, temperature and strain rate. Brittle potato products include crisps directly produced from the tuber and various snacks produced from the intermediate of dehydrated potato, although cereals offer probably the greatest variety of brittle products from a number of processing operations.

Brittle products are taken here to include the textural terms ‘crisp’, ‘hard’ and ‘crunchy’. An alternative definition of ‘brittle’ may be found in the polymer engineering literature. Powell (1983) characterised brittle failure by the creation of new surfaces and fragmentation after the polymer has deformed to a small extent and Ward (1983) designated brittle behaviour from the stress–strain response as failure at the maximum load which would normally occur at low strains. In contrast ductile behaviour results in a load maximum before failure. Rapid loading tends to favour brittle failure; the implication of the rate of eating in the texture of foods is a further complication.

Composites

Different textures may be produced by the fabrication of composites. Foams represent a special case where the material occupies the foam walls; the lower density of a foam results in reduced stiffness and strength compared to an isotropic solid with correspondingly modified textural properties (see Jeronimidis, this volume). In general, composites make use of components of different properties and it is interesting to note that in synthetic materials engineering inclusions are made in the matrix to toughen or stiffen the component.