Fundamental Considerations Concerning Dough Rheological Elements and Dynamic Mixing Parameters

Abstract

At the beginning of mixing, the dough formulation components form agglomerates as a result of their mobility, damping, swelling and solubilization. These agglomerates become distributed at a speed dependent on the shear gradient of the mixer. The timing of these processes within the dough mass proceed more evenly, and parallel to one another, when the components become mixed with each other to form the thinnest possible layers as rapidly as possible. This process results in the formation of hydrogen bonds, and other intermolecular cross-linking, and explains why water binding occurs more rapidly with increasing number of turns of the mixing-head, as does the increase in dough effective viscosity. The increase in effective viscosity, using a constant number of revolutions, results in a higher turning moment, or torque, and shear gradient. Since the specific mixing intensity is a function of the number of revolutions, shear gradient and mass of dough, the mixing intensity changes considerably with changes in the revolutions of the mixing-head and shear gradient, with a constant dough mass. Mixers of different geometrical construction as regards mixing-elements and mixer bowl design working at the same rpm will not therefore deliver the same mixing intensity. The commonly used concept of expending a fixed amount of energy on or work input to the dough mass cannot be regarded as a reliable dynamic mixing parameter. The reason is that the energy expended, depending on mixing intensity and mixing time, contributes not only to dough structural build-up, but also to irreversible structural breakdown and rheological deformation of the dough. This latter process leads to energy being transformed and dissipated as heat and cannot be regarded as cost-effective or energy-effective.