Appropriate operating condition for golden color parboiled rice production by high temperature fluidized bed drying and tempering

Golden color parboiled rice is practically obtained by a high steaming temperature and a long steaming time. Under this condition, there is a splitting of the rice endosperm, which causes poor head rice and uneven color of parboiled rice grains. In this work, it was therefore proposed to use high temperature fluidized bed drying and tempering for producing golden color parboiled rice. In the experiment, the paddy was soaked in hot water at 70 °C for 5 h, steamed at 103-117 °C for 5-30 min, dried at 110-150 °C to a moisture content of 25% dry basis, and tempered for 30-90 min. The experimental results showed that the degree of starch gelatinization depended on the temperature and the duration of steaming. The gelatinization of rice starch in the steaming step affected the drying rate and effective diffusion coefficient. The head rice yield of the final product ranged from 71-72% and was independent of the drying temperature. The obtained parboiled rice had a golden color, corresponding to the whiteness in the range of 22-24, when the drying temperature was above 130 °C and tempering time was at least 30 min. It was recommended that the soaked paddy should be steamed at 110 °C for 10 min, dried at 150 °C and tempered for 30 min. Under the recommended condition, the parboiled rice was in the “highly parboiled” category, and the total energy consumption was 3.94 MJ/kg wet paddy.