Grain roasting and popping are important unit operations for manufacturing ready to eat products of longer shelf life. Change in moisture content and volume of grain during roasting leads to development of internal pressure for popping. A mathematical model, considering thermodynamic changes and heat and mass balances during roasting, was thus developed. The predicted internal pressure, moisture content and change in volume at 2.8 min roasting time and at 213 degrees C grain temperature, while roasting pan temperature was 335 degrees C, were found to be about 45 MPa, 14 % (dry basis) and 130 mm(3), respectively. The accuracy of the model's results was examined by comparing the predicted and measured values of changes in volume and moisture of the grain during roasting. Prediction performance of the developed model was found to be satisfactory. (c) 2005 Elsevier Ltd. All rights reserved.