Modelling of bread dough aeration during mixing: Experimental investigations using scale-up mixers

Abstract

Aeration of bread dough during mixing in three scales of Tweedy-type mixers was studied using a model, which defines the entrainment and disentrainment coefficients. The model describes dough aeration as a dynamic balance between the rates of entrainment and disentrainment of air during mixing. Experimental investigations were performed by measuring the change in density of dough in accounting its air content following a step change in headspace pressure in the mixer halfway through mixing. Doughs made from premium grade quality flour were mixed for two minutes in the high speed mixers; the pressure was then changed and mixing continued for a further two minutes. The density of dough samples taken following the pressure change was measured using a double-cup buoyancy technique. The effects of both a step increase and a step decrease in the headspace pressure were investigated. The value of the disentrainment coefficient was greater following a step decrease in pressure compared with a step increase for all the three mixer scales, although there was not any clear trend observed in the three mixers scales. This confirmed the earlier results of disentrainment enhancement when pressure is reduced midway through mixing despite the different mixer scales. The slight increase of entrainment ratio with mixer scale seems to agree with the excessive aeration problems in scale-up mixers used in the industry.