Joint International Conference on Long-term Experiments ...

WATER DIFFUSION IN BREAD DURING BAKING
Ruska L.*, Chereji Rodica**, Purcărea Cornelia**, Timar A.**
* Bakery Bicaciu
** University of Oradea, Faculty of Environmental Protection
ABSTRACT
A study of heat and water transport in bread during baking was performed. Loaves of bread
were fermented twice and baked in a conventional ven at 225 0 C, with no forced convection,
for 35 min. The local water content and two or three different temperatures were measured
inside the bread during the baking process. Bread baked from wheat flour was used to
investigate the mechanisms of water transport inside a loaf during baking. The water
content was measured in the centre, 1 cm from the base, in the bottom crust, 1 cm under the
top surface and in the top crust. The temperature was measured on the bottom surface, in
the centre, and 1 mm from the optic fibre. The results indicate that up to 70±5 0 C, where a
structural change is taking place, the water content in the centre changes little. However,
after reaching this temperature the water content in the centre of the loaf rises due to
vapour transport from the warmer regions. The water appears to be moving towards the
coldest region, and not towards the geometrical centre.
Keywords: water; diffusion; transport; baking; bread
INTRODUCTION
During baking, starch is gelatinised and proteins are denaturated. The denaturation of
proteins releases water while the gelatinisation of starch absorbs water. These two
phenomena occur during the same temperature interval of 60-85 0 C, and contribute to the
change from dough to crumb (Marston, P. E. and Wannan, 1976). The temperature-rise at
the surface and heat transport towards the centre also involves water diffusion
(Thorvaldsson, K. and Skjoldebrand, 1996) and therefore a change in the water content
distribution.
The water content affects the gelatinisation of the starch Kokini, J. L., Lai, L. S. and
Chedid, L., 1992) and the final quality of the bread. During baking, the water content on the
surface of the loaf becomes lower than in the centre. This, in combination with the high
temperature, is one of the factors that makes the crust different from the crumb. An example
of a reaction that is affected by the water content and contributes to the crust formation is
the Maillard reaction, which results in the browning of the crust and the development of
bread aromas (Skjoldebrand C., 1986). Conversely, the starch gelatinisation and the protein
denaturation affect the diffusion of water by absorbing and releasing water. This makes the
baking process very complex. In 1972 Auerman suspected that the water content rose in the
centre of a loaf during baking, due to evaporation and condensation. Both Sluimer and
Krist-Spit, 1978 and de Vries et al. 1998 found an increase in the water content, with 3.5 g
water 100 g bread in the centre of the loaf immediately after baking.
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