Aeration during bread dough mixing: I. Effect of direction and size of a pressure step-change during mixing on the turnover of gas

The aeration of bread dough during mixing has previously been modelled as a balance between gas entrainment and disentrainment into and out of the dough, from which the gas turnover time was determined. This paper tests this model by mixing dough in a high-speed Tweedy-type mixer which undergoes a pressure step-change midway through mixing. The volume of gas entrained in the dough following the pressure change was calculated from its density. The volume of gas entrained was found to reach a steady state much more quickly following a pressure step-decrease than an increase, appearing to signify gas turnover rates over twice as large. Thus, gas disentrainment was found to be enhanced following a pressure step-decrease in a manner not incorporated into the model. The size of the pressure step-decrease did not appear to affect the gas turnover time, but increasing the pressure step-increase size decreased the gas turnover times. The weak flour doughs exhibited higher gas turnover rates during mixing than the strong flour doughs, in both pressure step-change directions and at all step-sizes. © 2004 Institution of Chemical Engineers.