Crust setting during bread baking as studied by a baking model

A model baking was previously developed in order to better understand transport phenomena and bubbles formation inside dough. In this model the coupled mechanisms heat transfers, mass transport and mechanical behaviour inside dough were formalised and validated by experiment. In the present study, from model the crust setting and its special behaviour were specifically focalized. Simulations make it possible to study the influence of various parameters that govern the crust setting and its characteristics such as thickness and porosity. First of all, on the basis of a literature review, the crust was defined as the dry zone' where the water content was inferior to 0.16 kg/kg of dry matter. The mechanisms responsible for global water loss and crust setting first proposed were validated for multiple operating conditions: water loss is essentially driven by heat transport and to a lesser extent by the mechanism of water transport by evaporation-condensation-diffusion, in the crust and in the crumb beneath the crust respectively. After, a sensibility study of the parameters that driving this mechanism were evaluated. Every parameter affecting the porosity in the dry zone also has an effect, in most of cases of the same order, on the total water lost by the loaf, for example: initial porosity of dough, temperature of stiffening in the dough film (due to starch gelatinisation and/or protein coagulation), occurrence of the rupture in film, and water activity of dough. From this study it was possible to hierarchy the key parameters from a technological point-of-view; oven air temperature and more generally the ratio between top and bottom heat fluxes, were ranked as a primary parameter affecting the crust setting and the water loss, suggesting a possible control through the process.