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International audience; Gas generation and dough mechanical resistance inside bread drive the bubble growth during bread making. The objective was to evaluate the impact of a lowering in external pressure on bread expansion during baking. It was evaluated by numerical vacuum baking simulations ans MRI experiments.

International audience; Poster qui présente la méthodes cuisson sous vide.

International audience; Crust and crumb come from the same original dough, but their properties differ due to a distinct local heat-moisture treatment. Stiffening of crumb, but also of crust, is known to affect dough inflation and squeezing. Past studies focused on dough rheology considered at best the effect of temperature at constant dough water content. This study aimed at characterizing the effect of heat-moisture treatment on dough rheology. Dynamic mechanical thermal analysis DMTA applied to a dough strip was retained and the heating rate in the DMTA oven was varied. Temperature and water content in dough were monitored and compared in the state diagram. High heating (drying) rates (>15°C/min) were relevant of a top crust, while lower heating rates (5°C/min) were rather relevant to the bottom crust during pan baking. At high heating rates, dough viscosity behaved as if water content was kept constant and as long as temperature remained below 80°C (stage A). Conversely to high heating rates, complex viscosity at low heating rates increased with decreasing water content; this was attributed to the enhanced distribution of water at the microscopic scale. The decrease in viscosity observed above 80°C in samples at constant water content was not observed whatever the heating rate, and replaced by a long-lasting plateau (stage B); this was related to a value in water content below approximately 37%, common to all drying rates. The range of water content over which stage B took place increased with higher heating rate, possibly affecting the degree of starch gelatinization. This implied that the higher the heating rate, the lower the complex viscosity in stage C (factor of 2). Above the ebullition temperature of water, the logarithm of complex viscosity increased linearly with water content (stage C), at a rate independent on the heating rate.

International audience; The present model is compared to experimental baking, and its underlying hypotheses discussed. For the first time the rheological dough properties imputed into the model was related to the local temperature and water content. Temperature and water content profiles, overall water and CO2 losses were monitored during baking; overall and local expansion were monitored in real time by IRM. Rheological properties were previously determined by DMTA and a specific viscosity model in function of local temperature and water content integrated. Model equations were solved numerically using a finite element method via COMSOL Multiphysics Software. Experimental trends were correctly correlated, providing a satisfactory qualitative validation of the model. A sensitivity analysis of different parameters of driving overall expansion mechanisms was undertaken through which it was possible to establish a correlation between the mechanisms responsible for the expansion. Only the levels of viscosity reached at the crust are not sufficient to stop the overall expansion. Under these conditions, the mechanisms controlling the expansion depend not only the viscosity forces, but on the relationship between the forces exerted by the crust (viscous forces) and the mechanisms which control pressure build-up and gas release at the bubbles. The study further established the needs to improve the rheological model and for local monitoring of key variables for appropriate interpretation of the interactive mechanisms taking place during the baking process.