When eating bread, most of us probably don’t think about the empty space in it, but rather whether we like its texture and flavour. Yet both of these are driven by bubbles. This is because one of the key aims when mixing is to ensure that air is trapped in the dough and, for sandwich and toast bread, we want the air to be evenly dispersed.
After mixing, dough is moulded and proved. In these steps the dispersion of air is modified, with a few of the bubbles collapsing, while most increase in size, so expanding the volume. At this stage, the bubbles are filled with both air and carbon dioxide gas from fermentation. When the dough is baked, further expansion occurs as the water boils to steam.
More regular bubbles ensure there are no large holes in the bread crumb, creating an even texture and a softer eating quality, so it is important to consider which factors might cause a change to their number and size. Among the many is the inclusion of bran in the dough, either through the use of wholemeal flour, or directly. Bran is ’thirsty’ for water, reducing the amount available for gluten development; we need this to create enough strength in the dough to stop the bubbles bursting as they expand. Also, the pieces of bran physically interrupt the gluten network, again reducing its ability to hold the bubbles. We overcome some of these problems with the use of ingredients, such as fat and emulsifiers.
=== Dr Campbell says: ===
"Bakers have made great strides in producing much more palatable wholemeal breads. Nevertheless, the vast majority of bread sold and eaten is still white, so it cannot be claimed that the problem has been solved. The amount of research devoted to wholemeal bread is a tiny fraction of that devoted to white bread. Understanding bubble behaviour, which has been so beneficial to white bread research, may well bring further improvements to wholemeal breads. Because this is a new and relevant way of viewing this type of bread, it is bound to give new insights that might translate into commercial applications that would indeed improve consumption."