This project is a continuation of research begun in 2004 that initially investigated the use of infrared and radio frequency for disinfestation of insect pests in rough rice. Results showed that infrared could be used in storage rice with no milling quality loss, so research in 2006 focused on whether this technology could also be used for rice drying with improved efficiency and quality.

Freshly harvested M-202 rice from Farmers’ Rice Cooperative was used in infrared drying tests. Rice samples with different initial moisture content – from 20.6 percent to 25 percent – were dried with infrared under three different rice bed thicknesses ranging from 2mm to 10 mm for 30 second intervals between one to two minutes.

The results showed that rice temperature rose quickly, depending on the thickness of the drying bed. Moisture removal during heating was more a function of rice temperature than rice bed thickness. Tempering rice samples by keeping them heated in closed containers results in higher moisture removal during cooling and, ultimately, higher milling quality.

Moisture removals of rice samples with different initial moisture contents after heated to various temperatures

Slow, forced-air cooling also significantly increased moisture removal during cooling. However, using forced air caused fissuring and thereby reduced milling quality. On the other hand, all samples with tempering and slow cooling had high milling quality.

This research suggests that infrared technology could effectively be used to dry rice at a high rate with tempering and slow cooling to achieve high milling quality. Further research is needed to study the effect of preheating of drying bed on required heating time, moisture removal, and milling quality of rough rice. Nonetheless, these findings could lead to new rice drying practices and rice dryer design.