Water transfer in bread during staling: Physical phenomena and modelling

Starch retrogradation and water loss have effects of the same intensity on the increase in firmness in the phenomenon of bread staling. Writing the equations of this system, in order to understand the mechanisms of water transfer in the vapour and liquid phases, is apparently simple. Nevertheless, choices are necessary for the simplifying hypotheses. Two models, differing in their geometry and their equations, were developed. Besides investigating the water transfer mechanisms in the vapour and liquid phases, the aim of this study is to compare the results of the two models and to conclude as to their individual interest. Concerning the physical phenomena, the study shows that a part of the water lost by the crumb escapes into the atmosphere while another part is absorbed by the crust. As regards the modelling the study shows that the most complete model is not the best choice and specifies the simplifying assumptions that should be retained or eliminated.