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Fig. 18 Four-piecing of bread doughs.

Fig. 18 Four-piecing of bread doughs.

6.8 Can you explain the role of energy in the Chorleywood Bread Process?

The transfer of mechanical energy to the dough during mixing with the Chorleywood Bread Process (CBP) is an essential component in the development of a dough with specific rheological properties and the necessary gas retention to produce a loaf of optimum volume and crumb cell structure (Cauvain, 1998). When first introduced the 'optimum' work input level for the CBP was reported as 11 W h/kg dough in the mixer but later work has shown that the optimum total work input varies with the type of flour being used, see Fig. 19 (Cauvain, 1998; Gould, 1998).

The role of energy in the CBP has still to be fully explained. It is very likely that the high-energy inputs are capable of mechanically breaking the disulphide (—S—S—) bonds holding the original protein configurations. In this way mechanical energy can be likened to the effects of natural (enzymic) or chemical reduction. This may explain in part why the addition of a chemical reducing agent such as L-cysteine hydrochloride is considered to reduce the energy required for dough development.

Chamberlain (1998) - one of the co-inventors of the CBP - considered that only about 5% of the available energy was required to break the disulphide bonds. A significant part of the energy input during CBP dough mixing will be taken up with the mixing of the ingredients and breaking weaker bonds. In breaking the disulphide bonds energy may well play a role in opening potential sites for oxidation. The CBP may therefore be considered as a redox-type process, in this case a combination of mechanical reduction and chemical oxidation rather than a purely chemical one.

As we consider the role of energy in the CBP we must recognise that a fundamental difference between CBP-compatible and other mixer types is the rate at which energy is delivered. You can increase the total energy imparted to doughs by lengthening the mixing time but the effect on bread quality is not as good as if the same total energy is delivered at a faster rate. In the original CBP the delivery of energy was needed within two to five minutes of mixing and the same premise holds true today, even when flours that require more than the original 11 W h/kg are used.

In addition to noting the rate effect we should also recognise that the input of energy to the dough is manifest as a significant temperature rise and that the provision of suitable quantities of chilled water are required. It may even be necessary to employ a cooling jacket of some form so that final dough temperatures can be maintained at acceptable levels, typically around 30 °C.

Fig. 19 Effect of work input: (a) 5; (b) 8; and (c) 11 Wh/kg dough.

Fig. 19 Effect of work input: (a) 5; (b) 8; and (c) 11 Wh/kg dough.

References

CAUVAIN, S.P. (1998) Breadmaking processes, in Technology of Breadmaking (eds S.P. Cauvain and L.S. Young), Blackie Academic & Professional, London, UK, pp. 18-44.

CHAMBERLAIN, N. (1998) Dough formation and development, in The Master Bakers Book of Breadmaking, 2nd edn (ed. J. Brown), Turret-Wheatland Ltd, Rickmansworth, UK, pp. 47-57.

GOULD, J.T. (1998) Baking around the world, in Technology of Breadmaking (eds S.P. Cauvain and L.S. Young), Blackie Academic & Professional, London, UK, pp. 197-213.

6.9 We are using the Chorleywood Bread Process to develop our doughs and apply a partial vacuum during mixing to produce a fine and uniform cell structure in the baked loaf. Sometimes we observe that the cell structure becomes more open even though the vacuum pump is still working. What is the cause of this problem?

The application of partial vacuum (typically 0.5 bar) during dough mixing with the CBP is used to produce a fine (smaller average cell size) and more uniform cell structure in the final baked loaf (Cauvain, 1998a). It does this by shrinking the size of the gas bubbles present in the dough. At the same time it reduces the total quantity of gas in the dough (Marsh, 1998) which gives improved divider weight control and yields a dough that feels 'drier' to the touch. The latter effect has allowed users of the CBP to increase the added water content at dough mixing to deliver a dough consistency similar to that obtained with bulk fermented doughs with lower water contents (Cauvain, 1998a).

The process of dough expansion depends on the presence of nitrogen gas bubbles in the dough, because the oxygen in the air bubbles originally incorporated during mixing is lost because of yeast action (Chamberlain, 1979). The nitrogen gas bubbles provide the sites into which the carbon dioxide gas generated by yeast fermentation can diffuse. This nucleating role is critical since carbon dioxide itself cannot form a gas bubble in bread dough (Baker and Mize, 1941). Without sufficient nitrogen gas bubbles being present in the dough you cannot form a 'normal' bread cell structure.

The numbers of gas bubble nuclei in the dough are considerably reduced as the mixer headspace pressure falls closer to 0 bar. In practice most vacuum pumps fitted to CBP-type mixers are designed to run around 0.5 bar because lower pressures tend to give coarser and more open cell structures. We suggest that you discuss the operation of your vacuum pump with your engineers and equipment suppliers. Though rare, it does appear that the source of the problem is that the pump at times is operating at pressures much lower than 0.5 bar.

In addition to the coarse open cell structure a characteristic of this problem is that there is extensive blistering of the crust which also has a waxy, greasy or oily appearance, somewhat similar to that seen on retarded pan breads (Cauvain, 1998b).

References

BAKER, J.C. and MIZE, M.D. (1941) The origin of the gas cell in bread dough.

Cereal Chemistry, 18, January, 19-34. CAUVAIN, S.P. (1998a) Breadmaking processes, in Technology of Breadmaking (eds S.P. Cauvain and L.S. Young), Blackie Academic & Professional, London, UK, pp. 18-44. CAUVAIN, S.P. (1998b) Dough retarding and freezing, in Technology of Breadmaking (eds S.P. Cauvain and L.S. Young), Blackie Academic &

Professional, London, UK, pp. 149-179. CHAMBERLAIN, N. (1979) Gases - the neglected bread ingredients, in Proceedings of the 49th Conference of the British Society of Baking, British Society of Baking, pp. 12-17. MARSH, D. (1998) Mixing and dough processing, in Technology of Breadmaking (eds S.P. Cauvain and L.S. Young), Blackie Academic & Professional, London, UK, pp. 81-119.

6.10 We are using spiral mixers for our bread doughs. What is the best mixing time to use?

There is no simple answer to this question because it depends in part on the type of spiral mixer you are using, your product range and the product quality you are seeking. Most spiral mixers have two operating speeds: a slow one mainly used to disperse the ingredients and a faster one used to develop the dough.

Spiral mixers typically operate at lower speeds than CBP-compatible mixers and thus in a given mixing time cannot impart as much energy to the dough. The actual transfer of energy to the dough with spiral mixers depends to a large extent on the configuration of the mixing blade, and those designs that have more than one mixing blade will transfer a greater quantity of energy to the dough in a given time. Thus, for a given mixing time we will expect to see differences in those aspects of bread quality that are related to dough gas retention, such as volume and softness, and to a lesser extent fineness of cell structure. We can expect that the greater the energy transfer, the larger the bread volume and the softer the crumb.

For any given spiral mixer increasing the mixing time will increase the total energy transferred to the dough. The longer the mixing time, especially on second speed, the greater the total energy and the larger the bread volume. However, since spiral mixers operate at lower speeds than CBP-compatible mixers we cannot expect to achieve the same total energy levels that are possible with the CBP.

To determine your optimum mixing time we suggest that you carry out a series of trials in which you start with your existing mixing times, if you have them, and raise the second speed mixing time by 2 minutes for successive doughs. If you do not have an established second speed mixing time start at, say, 6 minutes, use 8 for the next dough, and so on. You will probably find that you need not go beyond 14 minutes.

It is important to have the same final dough temperature at the end of mixing so that you can make a true comparison. The longer the mixing time, the greater the transfer of energy and so the greater the temperature rise in the dough. This can be compensated for by lowering the water temperature that you use in doughmaking. Each 1 °C that the dough temperature requires adjustment by will require at least 2 °C change in water temperature.

It is also important that any trials are carried out with the same dough mass in the bowl because energy transfer with spiral mixers depends on the degree of interaction between dough and spiral beater. For a given mixing time this interaction increases as the mass of dough goes down, within limits, and vice versa.

When you have completed your trials you will probably see that bread volume increases as mixing time increases, reaches a maximum at about 10 or 12 minutes and then begins to fall slightly. This will indicate the optimum mixing time for your particular spiral mixer. The same time can be used for a range of different bread types, assuming that maximum bread volume and crumb softness are your aims.

6.11 Why is it necessary to control the temperature of bread doughs?

The control of final dough temperature to a constant value is essential to ensure consistency of product quality whatever the breadmaking process that is being used because almost all of the chemical and biochemical processes involved in breadmaking are temperature-sensitive. In addition many of the physical properties of dough that influence its processing are directly affected by changes in temperature.

The most obvious of the processes in breadmaking that is temperature-sensitive is gas production by the yeast and variations in dough temperature will be reflected in variations in proving volume, even in a controlled prover environment. In many bakeries variations in proving volume cannot be compensated for by changing proving time and so variations in bread volume and quality would follow. Yeast activity increases as the temperature increase, reaching a maximum at about 43 °C.

A complex series of enzymic actions takes place in fermenting dough and all of these are temperature-sensitive. As with yeast, enzymic activity increases as the temperature rises though the temperature varies at which maximum activity occurs according to the particular enzyme. In breadmaking processes that employ significant periods of bulk fermentation as part of the development stage, variations in dough temperature will have a profound effect on bread quality.

Even the chemical reactions, such as ascorbic acid-assisted oxidation, are affected by temperature. Lower temperatures give less oxidation and hence yield doughs with a reduced ability to retain gas in the oven.

If the temperature of the dough at the end of mixing is raised then the rheology of the dough will change; it becomes less viscous and easier to deform. In turn this results in less moulder damage. However, if the dough temperature is raised too high, then it becomes too soft to process. If the dough temperature falls, then the dough becomes stiffer and moulder damage will increase.

The choice of dough temperature to use is closely linked with the breadmaking process being used, with higher dough temperatures being used with no-time doughs than those that will experience bulk fermentation or significant processing times.

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