FAYETTEVILLE, Ark. – Bringing in a microwave to dry harvested rice could do more than just get the job done faster. Researchers in the University of Arkansas System's statewide Division of Agriculture seek to use it to prevent cracking of dried rice kernels and maintain milling quality.

The Department of Food Science is working with equipment on loan from AMTek Microwaves of Cedar Rapids, Iowa, to determine the capabilities.

“This is new for rice, especially for drying rice,” said Griffiths Atungulu, an assistant professor of grain processing and engineering in the department who is leading the research effort. “Traditionally, rice has been dried in the U.S. using natural air in-bin, and heated-air, high-temperature cross-flow drying systems. The microwave is another potential new technology. We are working with AMTek to see how we can optimize the new technology to maintain quality of the dried rice.”

Atungulu sees considerable potential for microwave drying and the benefits it can offer in rice processing. Microwave dryers use volumetric heating – heating the entire kernel nearly all at once – that may allow for rapid drying. The volumetric heating of rice accorded by microwaves reduces chances of high moisture content gradients developing in the rice kernels, which in turn reduces the likelihood of kernels cracking from stress.

When such cracking is prevented, the kernels are less susceptible to breakage during milling. Breakage can reduce the rice milling yield, which has a negative economic impact for rice producers and processors.

“One of the things we look for is to dry rice quickly, but in ways that maintain rice quality in terms of milling, nutrition, sensory, and functionality.” Atungulu said. “Rice milling quality is very sensitive to moisture content and temperature gradients encountered during drying. This particular equipment is designed with modular processing features, which we hope to optimize with an optimal goal that rice could be dried to safe storage moisture content in a single pass and not introduce huge moisture content gradients that might produce fissures or cracking.”    

Atungulu also sees some potential for using the technology to achieve not only drying but also disinfestation and decontamination of any insects that may be deleterious to rice quality during storage.

The research project being pursued by division researchers would be on a pilot-scale using the AMTek microwave and other facilities on campus. The results could be applicable on a larger industrial scale. Atungulu said that it is important to experiment with various bed-layer thicknesses on the conveyor belt to determine drying characteristics. The microwave energy supplied to mass amounts of rice such as would be the case in a scaled-up process should take into account the thickness of the rice bed and initial moisture content.   

“Those are some of the parameters we need to define very carefully.” Atungulu said. “What is that optimal bed thickness? What intensity of heat does the microwave correspond to that will give us desired drying duration and product quality for rice at a given initial moisture content? Those must be determined before anyone can begin thinking about scaling up for industry.”

The research team expects to work on the project while testing different cultivars of rice and at different seasons. The company’s equipment is on loan throughout that process, said Stephen Rogers, AMTek vice president.

AMTek joined with the Division of Agriculture after the company was asked by a foreign nation to develop a rice drying machine, Rogers explained. He said AMTek personnel weren’t familiar with rice drying techniques, but then they discovered papers on the topic written by Atungulu and Terry Siebenmorgen, director of the Division’s Rice Processing Program.

“So we contacted them and have been working to establish this relationship to have them help us figure out how to dry rice using microwaves,” Rogers said. The project is expected to take three years.