Dough aeration and rheology: Part 1. Effects of mixing speed and headspace pressure on mechanical development of bread dough

Abstract

A laboratory-scale Tweedy-type mechanical dough development mixer was modified to monitor work inputs of dough during mixing through a computerised data acquisition system. Recorded torque showed a curve that increased to a peak about midway through mixing. Using this system, the effects of mixing speed and pressure on the development of doughs made from strong and weak flours mixed to a work input of 40 kJ kg −1 were studied. Mixing was characterized in terms of peak torque and torque at the end of mixing (end torque), and in terms of the number of blade revolutions at these two reference points. The peak torque and the end torque both increased with increasing mixing speed. The peak torque increased with increasing mixer headspace pressure, but the end torque did not. The number of blade revolutions to both the point of peak torque and to the end of mixing decreased with increasing mixing speed for both flours, implying dough development at higher speeds was more efficient. Increasing headspace pressure reduced the number of revolutions to the peak, but not to the end of mixing. These results provide evidence that achieving dough development is not independent of mixing speed in Tweedytype mixers, and that dough aeration, as affected by mixer headspace pressure, affects dough rheology and hence development in the mixer.

Dough aeration and rheology: Part 2. Effects of flour type, mixing speed and total work input on aeration and rheology of bread dough

“…Doughs from the strong flour, President White, and weak flour, Soft Patent, were mixed in the Tweedy 1 mixer using the system described in Part 1 of this series 16 at three mixing speeds, low, medium and high, ranging from about 40 to 70 rad s −1 , and at three headspace pressures, high vacuum (0.07 or 0.17 bar absolute), atmospheric (1 bar) and high pressure (2 bar). The work input levels were 10, 20, 30, 40, 50 and 60 kJ kg −1 (however, results were obtained for only the first four levels for the low speed, as the dough failed to mix properly beyond a work input of 40 kJ kg −1 ).…”

“…(As noted above, measurements made at lower strain rates and higher temperatures are likely to give a better correlation with baking performance; the DIS-PDD should preferably be based on measurements made under these conditions.) This is more relevant than the point of peak resistance to mixing obtained from torque traces, 16 although less easy to measure. Figure 10 shows the total work input at DIS-PDD versus work input at peak torque for the current study.…”

Dough aeration and rheology: Part 3. Effect of the presence of gas bubbles in bread dough on measured bulk rheology and work input rate

“…1 The doughs were mixed in an enclosed chamber at five headspace pressures using air and nitrogen (above and below atmospheric), and at three pressures using a controlled oxygen:nitrogen mix. In the latter case the oxygen:nitrogen ratio was varied when mixing at different pressures in order to give a constant oxygen partial pressure of 0.2 bar.…”

Effects of composition on dough development and air entrainment in doughs made from gluten-starch blends

“…Although torque recording mixers will provide good information on ingredient hydration and gluten film development, the nature of air occlusion during mixing has to be characterized by measuring the air volume fraction and the bubble size distribution in the dough after mixing (Campbell et al, 1998). The amount of air entrained and its subdivision into a particular bubble size distribution depends on mixer type (Whitworth and Alava, 1999;Peighambardoust et al, 2010), headspace pressure in the mixer (Elmehdi et al, 2004;Chin and Campbell, 2005a), moisture content (Chin et al, 2005;Peighambardoust et al, 2010), mixing time (Campbell et al, 1998;Mehta et al, 2009) and ingredients (Chin et al, 2005;Mehta et al, 2009). Unravelling the various mechanisms operating during mixing, in order to understand how ingredients and mixing process parameters affect the resulting dough properties, is not a trivial task.…”

“…In the breadmaking process three important tasks are performed during dough mixing: (1) blending and hydrating ingredients (absorption of water by various flour components), (2) developing the gluten polymers in the dough to create a good gas retaining film structure, and (3) occluding gas bubbles into the dough and subdividing them (Baker and Mize, 1941;Campbell et al, 1998;Mehta et al, 2009). It is thought that these tasks interact during the mixing process (Hoseney, 1985;Chin and Campbell, 2005a) and the extent to which interactions do occur is likely to alter the properties of the mixed dough.…”