Aeration and rheology of bran-enriched bread dough during sheeting

  • Mohamed Albasir

Student thesis: Doctoral Thesis


Bread quality depends on the aerated structure of the baked loaf, which arises from the unique rheology of wheat flour doughs as a result of the viscoelastic behaviour of wheat gluten proteins. Development of this dough structure is an essential element of dough preparation, generally achieved in modern processes via high speed mixing; however, sheeting of doughs is potentially a more effective and energy efficient approach that gives superior bread quality. Meanwhile, inclusion of bran in the dough formulation enhances the healthiness of bread, but hinders the development of the gluten structure and the resulting quality and palatability of the bread. Using sheeting to enhance dough development could help to offset the damaging effects of bran and allow production of more appealing high fibre breads. Implementing sheeting in a commercial breadmaking operation is more difficult than the use of high-speed mixing; however, recently there have been moves to implement this technology commercially. There is therefore a need to understand in greater detail the development of bread dough by sheeting, and its interactions with bran and with the development of the aerated structure of bread.

The effects of roll gap and number of sheeting passes on dough development with or without bran were studied using two different mixers, the MajorPin mixer and the Tweedy 1 mixer. The maximum expansion capacity of yeasted doughs was measured using the Dynamic Dough Density (DDD) test, which is a sensitive indicator of the degree of development of the dough’s gluten structure. The effects of the level (5, 10 and 15%) and particle size (Coarse, Medium and Fine) of bran on dough development by sheeting were investigated by measuring maximum expansion using the DDD system and by measuring the springback of dough following sheeting. Effects on bread quality were assessed by measuring the volume of baked loaves using an EinScan 3D scanning system, and crumb structure quantified by texture analysis and by image analysis using the C-Cell bread analysis system. Effects of wheat bran level and particle size on water absorption were investigated using the Chopin Mixolab 2.

Sheeting of doughs without bran for up to 12 sheeting passes increased maximum expansion and springback for roll gaps of 6, 9 and 12 mm. In doughs with bran, maximum expansion and springback increased from 4 to 8 passes, then decreased following 12 sheeting passes, for roll gaps of 6, 9 and 12 mm. At 15% bran, maximum expansion and springback decreased, more for Fine bran particles than for Medium and Coarse bran. Fine bran was consistently the most damaging to expansion and springback, while Medium bran was consistently the least damaging, with Coarse in between. The consistency of these patterns across all the conditions indicates that there is an intermediate particle size and an intermediate number of sheeting passes that maximise gluten development. There is thus scope for bakers to optimise the development of doughs containing bran, by adjusting bran particle size and sheeting, in order to minimise the detrimental effects of bran on bread quality.

The effects of sheeting on expansion capacity during proving translated into effects on final baked loaf volume and hardness. Control doughs without bran gave the largest loaf volumes, and volume increased by around 10-13% as sheeting increased from 4 to 8 to 12 passes at roll gaps of 6 and 12 mm. Loaves were slightly larger after sheeting at a 6 mm roll gap, reflecting greater gluten development at the smaller gap. Bran decreased loaf volume, with Fine bran once again the most damaging and Medium bran the least, and with sheeting for 8 passes once again optimal compared with 4 or 12 passes. Despite the detrimental effects of adding bran, sheeting is effective in alleviating these effects by enhancing the development of the dough.

C-Cell and EinScan results showed that sheeting and the addition of bran affect the volume and structure of the final baked bread. At both roll gaps, 6 and 12 mm, the control bread without bran had a higher number of cells as sheeting increased from 4 to 8 to 12 passes, and the diameter and wall thickness of the cells was lower. Sheeting doughs with bran increased the number of gas cells in the baked loaf from 4 to 8 passes, but the number then decreased at 12 passes for all particle sizes of bran. Fine bran gave more cells than the Medium and Coarse bran, the latter giving the lowest number of cells with larger diameters and wall thicknesses, indicating a more open crumb structure.

Mixolab results showed that addition of bran increases water absorption. This effect increases with the increase in the level of bran and with the decrease in its particle size. The lowest Mixolab water absorption was recorded for the Coarse bran, which suggests that the time required to absorb water by large bran particles is longer than for smaller particles, which results in an increase in the development time of the dough and decreases the stability time.

The current work has expanded understanding of the effects of roll gap and sheeting on dough development with or without bran and on the quality of final baked bread, in order ultimately to enhance the commercial application of sheeting for bread manufacture.
Date of Award2023
Original languageEnglish
SupervisorGrant Campbell (Main Supervisor) & Mohammad Alyassin (Co-Supervisor)

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