Heat and Mass Transfer Characteristics of White Bread during Baking Process

Abstract

In order to investigate the heat and mass transport phenomena during baking process of white bread, variations in mass, temperature and moisture distribution of bread were measured during baking under various oven temperatures ranging 140-300°C, using the samples made by the same manner of a sponge-dough method. The thickness of the crust and the porosity distribution were also measured for the bread after baking. The temperature of the crumb asymptotically tended to an equilibrium temperature at about 100°C without regard to the baking temperatures. Considering the baking process as drying phenomena, the process started from the pre-heating period and terminated during the constant-rate period of drying. The constant drying rate appeared to be determined by the transfer rate ratio of heat to water-vapor across the crust and increased with an increase in the baking temperature. Moisture content of the crust layer decreased with increasing the baking loss ratio, which was defined as the percentage of mass lost during baking to the initial, while that of the crumb was maintained at an initial moisture content. The crust layer was separated from the crumb by an evaporation front of water, and its thickness increased proportionally with an increase in the baking loss ratio. No marked temperature dependence of porosity profile was observed, and its profile seemed to be fixed after the oven-spring of the dough.