if required. In such cases, the water level added initially is slightly lower than the optimum level to allow for the addition of extra water later during the mixing process (Russell Eggitt, 1975). Should subsequent doughs become too soft then a reduction in initial added water has to be made. In high-speed mixing processes, e.g. the CBP, the mixing time is very short, so assessment of consistency must be made quickly and there may not be sufficient time to fully disperse any additional water uniformly throughout the dough. With spiral mixing, the slower mixing and longer timescale make the addition of extra water more practical (Ahlert and Gerbel, 1993; Gerbel and Ahlert, 1994).
Figure 2.8 Breakdown of crumb cell structure with tight doughs.
quality defects on the dough surface, e.g. tearing or rupturing of the dough surface.
In addition to the adverse changes that may occur on the surface, more serious defects may occur within the dough matrix itself. In particular, the internal structure of the dough may suffer ‘damage’ as a result of breakdown of the gluten strands within the dough matrix. This may lead to the formation of undesirable large holes or hard patches in the crumb. The basis of the adverse changes in bread quality which may occur with tight doughs is shown in Fig. 2.8. Within the dough matrix, individual gas bubbles of varying sizes are stabilised by the surrounding viscoelastic gluten network (Fig. 2.8a). If sufficient pressure is applied to the dough, the gluten network may be broken by the force and this may allow the coalescence of two or more adjacent bubbles (Fig. 2.8b), or gas bubbles may be eliminated from the dough matrix and amalgamation of gluten strands may occur (Fig. 2.8c). After the amalgamation of adjacent gas bubbles, the lower internal pressure of the new, larger bubbles allows them to grow at a faster rate than other smaller bubbles and they may become ‘holes’ in the crumb. When gas bubbles are eliminated from the dough matrix during moulding there are no opportunities for their re-introduction and the amalgamated gluten network cannot expand
in the prover or the oven, hence the formation of hard, dense patches in the crumb. With a sub-optimal dough consistency both effects may be observed to differing degrees at different places within the bread crumb.
Doughs that lack water also exhibit greater elasticity and reduced extensibility, both of which increase the susceptibility of the dough to damage during dividing and shaping operations. There are limited opportunities to compensate for such deficiencies in dough rheology during post-mixing processing operations. Fermented doughs relax, i.e.
become less resistant and less elastic, with increasing resting time, so it is possible to compensate for tight doughs to some extent by increasing any first (intermediate) proof time given to dough pieces. The potential for increasing first proof time is limited by other changes that will take place in the fermenting dough, namely the decrease in dough density which occurs with the evolution of carbon dioxide gas from yeast fer-mentation. The higher overall gas content after first proof increases the susceptibility of the dough to damage during final moulding of the type described above.
Water plays a significant role in relation to yeast fermentation in that the carbon dioxide gas which is evolved first goes into solution in the dough water. This process continues until the solution is saturated;
thereafter the production of more carbon dioxide increases the pressure in the aqueous phase to such an extent that the gas comes out of solution to begin the inflation of the nitrogen gas bubbles present in the dough.
Any oxygen that was present in the dough from air incorporation is removed by the yeast (Cauvain, 2007a). If the density of dough is plotted against time after leaving the mixer, little change is observed in the first few minutes (see Fig. 2.9), which corresponds to the period during which carbon dioxide saturation of the dough water is being achieved.
In practical doughmaking, the rheological terms softness (resistance to deformation) and stickiness are often confused. It is possible to have doughs that are soft but not sticky and vice versa, or both soft and sticky.
Stickiness is most often observed when doughs are subjected to the forces of shear rather than straightforward compression. Many oppor-tunities for the shearing of doughs occur in post-mixing processes, es-pecially during dividing, rounding and moulding operations. Problems with doughs that exhibit stickiness during processing are often over-come by reducing the added water content and in some cases through the application of air-blasts to dry the surface of the dough during the first moulding stages (Marsh and Cauvain, 2007). The evaporation of a small amount of water from the dough surface helps to reduce dough stickiness while maintaining a high water level in the dough.
Figure 2.9 Changes in dough density after mixing.
Conclusions
Water plays a critical role in the formation of fermented doughs, and it is important that the ratio of water to flour and other ingredients is optimised so that the dough has the ‘correct’ rheological characteristics for processing after mixing. The optimum water level in a fermented dough is affected by the properties of the flour used and some other ingredients that may be present in the formulation, so determining the optimum level of water addition requires both measurement and expert opinion.
The role of water as a solvent and a means of achieving hydration of many of the recipe components is important, but often overlooked, in doughmaking. In some cases, e.g. in the use of brews and sponges, the preparation of solutions and soft doughs aids the mechanical operation of breadmaking plants.
As well as playing a key role in dough formation, water also plays a significant role in the control of dough temperatures and in turn in the activity of the yeast present in the formulation. Adjustment of dough temperature is best achieved by varying recipe water temperature be-cause other techniques for controlling dough temperatures (e.g. cooling jackets on mixers) have only limited potential.