The science of salt

31 July, 2009
With the Food Standards Agency's targets on salt reduction now clear, Baketran consultancy director Stan Cauvain explains the importance of salt to bread and why reducing it is likely to cause bakers more than a few headaches
Page 18 

With the recent publication of new targets for sodium reduction in processed foods, salt (sodium chloride) remains at the top of the bakers' list of product quality concerns.

Currently working towards the 2010 targets (1.1g salt per 100g bread, 430mg sodium average; 2012 targets: 1g salt per 100g bread 400mg sodium average), the plant baking industry has continued to collaborate with the Food Standards Agency (FSA) and other interested bodies and has made significant reductions in the salt levels used in modern plant breadmaking. Each reduction that the plant baking industry makes takes it deeper into unknown territory, as the role of salt in breadmaking, especially at the lower levels we now use, has yet to be fully understood or explained.

The most apparent change we see when salt levels are lowered is the change in product flavour. This is not surprising, since saltiness is considered by sensory scientists to be one of the primary tastes. The high solubility of salt means that its impact on our taste buds is immediate when we eat bread. So the overall impact of reducing salt levels is complex, because not only does salt have its own flavour impact, but our overall assessment of the 'flavour' of bread is changed as the balance of the different and often more subtle flavours of bread that come from ingredients and processing are changed. Salt has such a unique flavour that it is not just a question of using less salt and tossing in a (permitted) alternative.

The fact that salt can inhibit the fermentation of bakers' yeast is well-known and the need to balance yeast and salt levels has been a fundamental principle in breadmaking for many years. Fermentation to produce carbon dioxide occurs in all breadmaking processes - otherwise we would not get the light, aerated and digestible food that we call bread. In plant baking, the fermentation of the dough takes place after the bulk dough from the mixer has been divided and placed in the prover. For people less familiar with baking, this terminology creates confusion between the terms 'fermentation' and 'prove' but, as far as the dough is concerned, they are one and the same thing. The expansion of the dough in the prover and its continued expansion in the early stages of baking - as manifest in oven spring - rely on the dough being able to grow in a controlled manner. There is a balance to be struck between gas production (by the yeast) and gas retention in the dough and, once again, salt plays a key role in striking this balance and, in doing so, contributes indirectly to the fineness of the cell structure in the baked product.

Gluten connection

The least well-understood role of salt is the contribution that it makes to the development of the gluten network in the dough. Dough development is an ill-defined term, but is manifest in the dough property, described as 'gas retention'. Even less well understood is the contribution that salt makes to the collective properties of dough, referred to as 'dough rheology'. This property tells us about how the dough will behave under the stresses and strains of processing through the plant and how easy it will be to shape and process the dough pieces. One of the significant problems facing all bakeries is that lower salt levels yield dough that is stickier and more difficult to process. This has been known for some time and has recently been confirmed by research supported by the FSA and members of the Federation of Bakers.

Though the precise contribution that salt makes to controlling dough rheology has still to be explained, salt forms strong ionic bonds with the gluten network and the water in the dough. Mechanical processing subjects the dough to greater shearing forces than hand moulding and some of the bonds are broken, with the result that the dough is smeared across equipment surfaces - for example, the conical moulder drum - which then impedes the transfer of successive dough pieces in the plant and 'stick-up' ensues. During resting (first proof) some of the bonds are reformed and the stickiness is reduced but in the final moulder, the dough again experiences high shearing forces and increased stickiness.

In the craft bakery and, to some extent, the in-store bakery, coping with sticky dough in processing is often a matter of patience and reducing the rate at which dough pieces are fed into the processing equipment or dealing with 'stick-ups' through manual intervention. In a plant bakery running 2,000-8,000 loaves an hour, the options are more limited. Watching plant bakers having to un-stick a plant is painful - and even worse when you are the one that has to do it! You cannot stop dough from fermenting, so a 10-15 minute stoppage to clean through the plant is not just about the few pieces lost in the moulder, it is also about the dough that is already in the line; on a 6,000-unit an hour plant, a 10-minute stoppage equals at least 1,000 lost loaves. Along with wasted raw materials and energy, the cost implications are very significant.

As salt levels in bread have been gradually reduced, bakers have learned to adapt their processing to cope with the changes in dough rheology. Improved process control has helped a lot with the introduction of measures to limit the tendency for dough to stick to moulding equipment and processing belts. The challenges have been greatest for premium branded products, where the requirement is for high and consistent quality. The drag of sticky dough trying to pass through the final moulder can lead to misshapen dough pieces falling into the pan, with subsequent variations in shape and texture in the final product. This may be acceptable in some marketplaces, but the UK consumer of branded products is very discerning and does not readily accept quality variations or losses.

The use of air streams in dough processing has supported the efforts of plant bakers. However, there is a balance to be struck; too much air may cure dough stickiness, but will lead to problems of dough skinning, which is just as bad for product quality. The use of air streams needs to be focused on the critical processing points in order to be most effective - long gone are the days of standing a big fan by the rounder to blow air over the dough.

Need for research

With the new targets for salt levels announced, where does the plant baking industry go? Clearly there is a need for good, focused research to understand the functions of salt and the contribution that it makes to all aspects of bread production and quality.

There is talk of 'salt replacers', but finding a legally acceptable alternative that delivers all three functions described above will not be easy. Reformulation strategies will certainly play a part in achieving lower salt levels, but changes in dough processing perhaps have a bigger role to play. This may require the redesign of some aspects of dough-processing equipment, but care is needed to be sure that 'the baby is not thrown out with the bath water'. Premium breads have very specific qualities that attract consumers, so any change in processing should not be at the expense of product quality if we are to continue to encourage consumers to eat more bread, with its positive contributions to calcium and fibre to the average diet.





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