Coloring process of food surface by convective heating

Effects of hot air temperature and velocity on coloring process of a white bread have been studied under convective heating. The white bread was baked by the hot air impinging to the surface of the bread under an open conditi on. Experiments were performed for the wide variations of the air temperatu re, 100-400 degrees C, and the air velocity, 1.7-15.0 m/s. The variations o f the surface temperature and the surface color of the bread were measured with time. The coloring rate increased with the increase of the air tempera ture or with the increase of the air velocity. If the heating energy was fi xed to a certain value, the coloring rate increased with the increase of th e air temperature. II the air temperature was fixed to a certain value, the coloring rate increased with the increases of the total heat supply which was calculated from the heating energy and the baking time. The data of the surface color and the surface temperature showed that the surface color de pended only on the surface temperature but not on the air temperature, the air velocity, and the baking time, It suggested that the coloring process o f the food could be controlled by controlling the surface temperature which depended on the air conditions and baking time.