Effect of deep fat and hot air frying on doughnuts physical properties and kinetic of crust formation

The effects of temperature (150, 165 and 180 °C) and frying method (deep fat and hot air frying methods) on the kinetic of doughnut's crust formation and also crust features were investigated in this study. Results revealed that at high frying temperatures in deep fat frying method, a higher percentage of doughnut surfaces were covered with crust, while at low temperatures using hot-air frying process, the crust percentage of the doughnut was higher compared with those of other frying method. By decreasing the temperature of fryer, the difference between frying time of two methods reduced gradually in a manner that at 150 °C the frying time was the same for both methods. Formation of doughnut's crust in deep fat frying method started from its lower and lateral parts but for hot air method, the formation began from the upper surface. Doughnut's crust formation during deep fat frying was more dependent on temperature than that of hot air fried ones. Hot air frying of doughnut reduced crust roughness and created a smoother surface compared to the deep fat fried samples. Decreasing the frying temperature for both methods increased the crust roughness. The results of this research permit a better understanding of crust formation procedure in deep fat and hot air frying process.