Improving the design and operation of a tweedy dough mixer

Abstract

Compared with other cereals, wheat is special because the dough that it makes, when mixed with water and other ingredients, has the following unique properties:
1. It forms a viscoelastic material.
2. It has good gas retention since the diffusion of gases through the dough is small.
3. It sets when cooked to form a solid foam.

In the study of dough rheology, mixing and baking, each of these properties generates the need for different types of mathematical considerations. For the Goodman Fielder problem presented at the 1997 Mathematics-In-Industry Study Group (MISG) meeting at Melbourne University, it is the first of these three properties which plays the crucial role in any study of the efficiency of the mixing of wheat flour dough.

The group studied the mechanics associated with the mixing of a large 300 kg dough mass within a Tweedy mixer rotating at 360 rpm subject to a cycle time of 4 minutes and concluded:
1. The baffles along the side of the mixing chamber are essential for the elongation strains necessary for dough development.
2. The impeller blades should have a circular rather than rectangular cross section to reduce the stress concentrations in the viscoelastic dough mass that lead to a cutting rather than stretching motion.
3. A series of experimental tests needs to be performed to study the effects of: baffle geometry; mixing speed; and recirculating motions within the mixing chamber.