Reverse airflow drying of steamed paddy and its effect on the rice quality and energy consumption

Non-uniform drying and head rice reduction due to non-movement of paddy in common fixed bed dryers is one of the basic problems in rice milling factories. In order to investigate and provide a suitable drying method with the approach of creating uniformity in drying process, reducing losses, and saving energy consumption, a two factorial experiment in completely randomized design (CRD) was used. The factors were the initial moisture content (IMF) of paddy at two levels (16 and 18%) and drying method at 4 levels (one-way air flow, reverse air flow in 1 hour, 2 hours and 3 hours and then continuation of drying process the same as one-way airflow). The same drying air temperature and air velocity was considered for all treatments. In both moisture treatments, three hours reverse air flow drying has the highest head rice (75.7-75.86%) and the lowest energy consumption (41-49 MJ/kg water). The highest energy consumption with the amount of 79 and 67 MJ/kg water was belonging to the paddy with high and low IMC, respectively. In one way airflow, dried paddy in 10 cm from the bottom layers of dryer has the lowest amount of head rice (63.65%). In both moisture treatments, the results of mixed layers showed that one hour reverse air flow drying with values ​​​​of 68.28-68.68% had the lowest head rice. Also, drying method had no significant effect (P>0.05) on the cooking quality.