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Flour to bread – the critical stages for process control

S.J. Millar, D.G. Bhandari and M.B. Whitworth

Campden & Chorleywood Food Research Association, Chipping Campden, Gloucestershire, GL55 6LD, United Kingdom


The quality of any given loaf of bread is essentially a function of how closely it meets the expectations of the consumer. As such, different breads have different criteria for acceptability. As an example, tinned, sandwich bread would be expected to have a fine and uniform cell structure. These characteristics would be wholly unacceptable for baguettes or ciabatta, however, where a more open and random crumb structure is desired. To ensure that raw materials meet the requirements for a particular process, a wide range of techniques may be used to determine inherent properties and likely final product quality. The skilled operator will then assess how the raw materials will be affected by processing and make necessary adjustments as required. To control the entire process, therefore, an understanding of the properties of the variety or class of wheat used is required as well as the purpose of each of the processing stages and how to alter these as raw material properties vary. The control of each of these stages is, therefore, essential in generating the highest quality bakery products.

Wheat Variety Identification

Wheat trading within the United Kingdom is based on a system in which variety is a fundamental criterion of acceptability. To facilitate this process, varieties are grouped together as a function of their suitability for different food uses (bread, biscuit or cake) or for production of feedstuffs. Although individual varietal characteristics are seen as being of lesser importance for some of these applications, wheat attracting a premium (such as that for breadmaking) will typically have the variety to be supplied as part of the agreed specification. While this offers assurance of the functionality of the material for a particular end-use, it poses considerable problems for millers in the monitoring of the wheat at point of supply. For many years, acid-PAGE (Salmon and Burbridge, 1985) has been the technique used to give a final judgement on wheat variety but it is accepted that this is not sufficiently rapid for use at mill intake. Under routine operations, therefore, visual identification of variety is undertaken for each lot of grain received although it is recognised that this is an imperfect system. To address these issues, work has been undertaken at CCFRA over the last 12 years to develop systems for wheat varietal identification which have been based on capillary electrophoresis. Initially this was through the use of dedicated laboratory-based single capillary instrumentation but in the last 5 years, lab-on-a-chip technology has been developed to allow it to be applied to the problem (Figure 1). A system has been developed based on the Agilent 2100 Bioanalyzer using Protein 200 chips to generate protein profiles presented in either electrophoretic or gel-like form. A separate means of comparing these profiles to a library of wheat varieties has been developed in conjunction with Nonlinear Dynamics with a view to providing the support required for adoption by the milling industry in the United Kingdom (Bhandari and Pritchard, 1994; Bhandari et al., 2004). The profiles generated differ from those derived using acid-PAGE in having information about the HMW-glutenin subunits in addition to that from the gliadins (Figure 2). Having demonstrated the application of the approach, further work is now underway to include the broader range of wheat types and varieties necessary to support the use of the technique by the milling industry. Although as a technique the speed of analysis for a single chip is still slightly slower than is typically required at mill intake, a number of samples may be processed in rapid sequence on a single chip which allows for faster turnaround of suspect deliveries of wheat. This, in combination with the objective nature of the analysis makes it highly likely that lab-on-a-chip will become the method of choice within the cereals industry in the United Kingdom within the next few years.

Figure 1. The Agilent 2100 Bioanalyzer

Figure 2. Example electrophoretic profile and derived gel-like pattern

The impact of hydration on dough performance

The process of dough development is widely recognised as being critical in the production of high quality baked goods, particularly bread. For this to occur, flour particles first need to become hydrated to ensure sufficient molecular mobility. The hydration process is, therefore, fundamental to dough processing but has received relatively limited study in comparison with the biochemistry of gluten proteins and their interactions. This is partly due to the difficulty in hydrating flour without the input of mechanical energy, the action of which makes distinction of hydration and development processes impossible. Previously workers have produced doughs using a process whereby powdered ice is blended with flour and allowed to melt (Campos et al., 1996). The dough thus formed is fully hydrated even though the input of mechanical energy is minimised. Hydration using ice has been used to produce doughs which, following mixing for a range of mixing times, have been processed in a standard way to produce bread. Hydration was allowed to progress overnight using flour and ice alone while salt and yeast were added immediately prior to mixing. The results (Figure 3) demonstrate significantly increased loaf volume for doughs produced using hydration prior to mixing compared with those produced using water with no pre-hydration. While it is clear that that there were differences in crumb structure the results indicate that the underlying gas retention properties of the dough were enhanced. Although further work is required to determine the impact of enzyme activity during hydration, the work serves to demonstrate that in addition to dough rheological differences as reported previously, the impact of altered hydration approaches on bread quality is significant.


30s mixing

60s mixing

90s mixing

120s mixing

180s mixing








Using standard mixing







Figure 3. Effect of dough pre-hydration on bread production using Hereward flour (loaf volumes are for 800g loaves and are normalised to this mass)

The impact of flour properties on crumb structure development

During no-time dough mixing processes, the structure initiated after mixing forms the basis of the final product subject to development through subsequent processes. This is in contrast to that from processes where a bulk fermentation step is required. In such cases, the acts of knocking back and moulding play a significant role in generating the final crumb structure of the bread (Collins, 1982). To understand how differing flour properties exert an influence on the internal appearance of bread, X-ray computed tomography was used to follow structure development non-destructively. Changes occurring during proving were followed by inserting dough in a polystyrene proof cabinet which was then placed in a medical imaging scanner. The baking process was followed by transferring the proved dough to a glass oven heated using a stream of hot air. The flow rate and air temperature were adjusted to achieve comparable temperatures to those of a conventional oven and resulted in similar bake times.

Flour properties were shown to have an effect from the earliest stages in processing with dough at the beginning of final proof already showing clear differences. Doughs produced using a flour derived from wheat used for feedstuffs exhibited a more open structure at this stage than doughs produced using breadmaking flour. Intermediate proof is relatively short in the Chorleywood Bread Process (6 minutes in this case) and so it is likely that the structural differences at this point reflect the poorer characteristics of the gluten-forming proteins for the non-breadmaking flour and their inability to sustain large numbers of small gas cells during mixing and intermediate proof. The coarser structure observed persists throughout subsequent processing as would be expected for breadmaking process of this kind. It is interesting to note, however that the dough produced from the non-breadmaking flour lost a significant volume of gas during transfer from the proof cabinet to the oven. This in combination with the minimal oven spring achieved indicate that the limit of expansion for the gas cells had been reached by the end of proof and that the structure was already extremely fragile. In contrast the dough produced from breadmaking flour continued to expand during the transfer to the oven and generated considerable oven spring with noticeable compression of structure and cells along the sidewalls and under the crust.


Start of final proof

After final proof

Start of baking

End of baking

Non-breadmaking flour

Breadmaking flour

Figure 4. Development of internal bread structure during processing


  • Lab-on-a-chip technology combined with pattern matching software offers millers the opportunity to objectively and rapidly determine wheat variety at intake.
  • Hydration of flour is a key element of dough production and appears to play a critical role in determining the gas retention properties of dough.
  • Flour quality has a significant impact on the internal structure of bread and this effect is apparent from the earliest stages of processing.


Thanks are due to the Incorporated National Association of British and Irish Millers (nabim) for funding the work on wheat variety identification.


Bhandari, D.G. and Pritchard, P.E. (1994) Project Report No. 99, Home-Grown Cereals Authority, London.

Bhandari, D.G., Church, S., Borthwick, A. and Jensen, M.A. (2004) Automated varietal identification using lab-on-a-chip technology. Proc. 12th ICC Cereal and Bread Congress, 529.

Campos, D.T., Steffe, J.F. and Ng, P.K.W. (1996) Cereal Chemistry, 73: 105-107.

Collins, T.C.H. (1982) The creation and control of bread crumb cell structure. London: Thesis for the Insignia Award in Technology.

Salmon, S.E. and Burbridge, K.M. (1985) FMBRA Bulletin, 2: 78-88.

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