The role of fat in the stabilisation of gas cells in bread dough

Electron microscopy has shown that during dough mixing by the Chorleywood Bread Process, fat crystals develop a crystal-water interface as they emerge from droplets of shortening and that they then adsorb to the gas-liquid interface of bubbles. In this process, the interface surrounding each crystal coalesces with the gas-liquid interface of the bubble. This adsorption process was not observed when triglyceride was added to doughs in the form of oil. The expansion of bubbles during proofing leads to the adsorption of many more fat crystals as they are encountered in the aqueous phase. During baking, fat crystals melt and thereby make it possible for the crystal-liquid interface to be incorporated into the surface of the bubble as it expands. This transfer of interfacial material from crystals to bubble surface explains how the addition of shortening to dough allows bubbles to expand during baking without rupturing, thus producing high volume bread with fine crumb structure. It follows that the amount of interface transferred to bubble surfaces for any given weight of fat is inversely proportional to the size of the crystals in the shortening and that therefore shortenings containing small crystals are more effective in producing high quality bread than those containing large crystals. A mechanism is now proposed which, for the first time, explains the precise role of fat crystals in this process and why the addition of oil is not effective. (C) 1996 Academic Press Limited