How Interconnected Bubbles Affect the Bread-Making Process

A team led by Dr Sumana Chakrabarti-Bell of SCBM Consulting has explored the process of dough fermentation in real time using synchrotron x-ray tomography. This technique uses fast-moving electrons to produce intense x-ray beams, which are fired into the sample at various points in time while the sample rotates 360°. It then uses a reconstruction algorithm to build up the resulting x-ray images into a clear 3D image of the sample’s interior structure.

With this approach, Dr Chakrabarti-Bell’s team could scan and capture the coalescence of gas bubbles inside rising dough. The researchers observed that gas bubbles were mobile in all doughs, coalescing partially and disproportioning, forming larger clusters.

The team investigated Canadian Western Red Spring (CWRS), which contains 11% protein and is strong for baking. Bubbles percolated at 26% porosity over a percolation time of 36 minutes. Bubbles were small and coalesced slowly to form a massively interconnected, single bubble.

They then investigated Australia Wyalkatechm (Wylk), which contains 11% protein and is weak for baking. Bubbles were relatively larger, formed clusters faster, but percolated at the same porosity of 26%. The single bubble with a maze-like structure formed within 13 minutes.

Following percolation, dough rise comes mostly from the percolating bubble. When the latter spans the entire volume of dough, loaves are large with a uniform pore structure in the crumb. With fewer bubbles making up the percolating bubble, loaves become crooked and smaller, with defects in the crumb.

Gas bubbles, floating in the aqueous phase, move in-between gluten fibrils, and coalesce with each other when in contact. Eventually, this creates the single maze of inter-connected bubbles. In a low-viscosity aqueous medium, the rate of bubble coalescence is slow, enabling other bubbles to become part of the percolating bubble. Such doughs form good quality loaves. The reverse occurs when the aqueous phase viscosity is high.  

The viscosity of the aqueous phase is influenced by the quality of polysaccharides, such as Arabinoxylans, present in flour. To grow wheat for high-quality breads, care should be given to control the Arabinoxylans in the wheat endosperm. The researchers hope their discoveries will lead to true innovations for wheat and bread products, helping the industry meet consumer needs while enabling farmers to maximize the value of their crops in a rapidly changing world.