Effect of heating system on the evaporating process of food: Radiation and convection

Evaporating process of a white bread has been studied both for radiation and convection heating system. The white bread was baked in an open condition by an electric radiation heater for the radiation experiments and by a hot air impinging to the food surface from a nozzle for the convection experiments. The variations of evaporating rate and heat receiving rate were calculated from the weight loss and the surface temperature, respectively. The evaporating rate for the convective heating was higher than that for the radiative heating throughout the baking time. The heat receiving rate for the convective heating was higher than that for the radiative heating at the first period of baking. But, it decreased rapidly and then became lower than that for the radiative heating. The calculation of the energy balance of the bread at baking showed that 60% of the received energy was used for evaporation at first both for convective and radiative heating systems. In the case of the radiative heating, its value decreased with time. On the contrary, in the case of convective heating, its value increased to 90% and then decreases with time. It means that the evaporating process is governed not only by the received energy but also by the heating manner.