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Oct. 29, 2020
By Fred MillerU of A System Division of Agriculture@AgNews479
Download MS Word version
Related PHOTOS: https://flic.kr/p/UBsaWP and https://flic.kr/p/2jZACPR(EDITOR’S NOTE: Subjects are unmasked because photos were taken before COVID-19 precautions
FAYETTEVILLE, Ark. — Microwave technology may offer a faster drying system for rice
than conventional heated-air drying systems, said Griffiths Atungulu, associate professor
of food processing and post-harvest system engineering for the University of Arkansas
System Division of Agriculture.
Griffiths is co-principle investigator with AMTek Microwaves, a Cedar Rapids, Iowa,
company, on a $100,000 Small Business Innovation Research grant from the U.S. Department
of Agriculture’s National Institute of Food and Agriculture.
Rough rice is reaped, ideally, at a harvest moisture content of 19-21 percent, Atungulu
said. Before milling, processors must reduce the moisture content to a target of about
Conventional rice drying systems use natural air in-bin or crossflow column dryers.
In-bin drying can require many days to dry rice. Rice processors commonly use crossflow
column dryers, which direct heated air across a column through which rough rice falls.
Dryers can speed up the process but still take considerable time, Atungulu said.
Crossflow column dryers usually require multiple passes of the rice through the column
separated by tempering periods, which maintain the rice at a warm temperature. It
commonly takes about three passes through the crossflow dryer to reduce the rice to
12.5 percent moisture content.
Because tempering often takes place overnight, the drying process often takes two
days or more to complete, Atungulu said.
It also impacts head rice yield, the percentage of kernels that are at least three-quarters
of their original length after milling’ Atungulu said. The extended exposure to heated
air can cause fissures in rice kernels’ physical structure, making them brittle. Milling
the rice then results in breaking some of the fissured kernels, reducing the head
rice yield. Other factors, including environmental conditions and rice genetics, contribute
to head rice yield. In the U.S., head rice yield averages 55-58 percent of the total
“The yield could be lower, depending on prevailing environmental conditions during
harvest,” Atungulu said.
Using an AMTek microwave dryer about the size of a commercial restaurant oven, Atungulu
has developed a method of drying rice to the target moisture content of 12.5 percent
in a single pass under laboratory conditions, he said.
His goal was to develop a one-pass drying method that maintained head rice yield at
or above the national average. He looked for a microwave drying method that did not
adversely affect rice color or flavor or increase rancidity, which can occur in the
bran layer. “We didn’t want to change anything that would affect consumer acceptance
of rice products,” he said.
AMTek is providing a large microwave drying oven that will allow Atungulu to advance
his single-pass rice drying process to a commercial scale. “This will be a proof-of-concept
study,” he said, “based on extensive preliminary research.”
In years of preliminary research, collaborating with AMTek and several rice processing
companies, Atungulu showed that a microwave frequency of 915 Megahertz — most home
microwaves operate at a maximum of 2.45 MHz — could dry rice in a single pass with
less impact on head rice yield. It also met the requirement of not affecting consumer-desired
color or flavor.
In the proof of concept, Atungulu has two goals. “First, we have to satisfy the rice
processors,” he said. “We want to demonstrate that microwave drying reduces the time
required for drying rice while reducing fissuring to improve head rice yield.”
Atungulu’s target is to improve the national average of 55-58 percent head rice yield
to at least 65 percent. “That would translate to a $145 million increase in rice value
annually,” he said.
Also, a microwave drying system requires a smaller machinery footprint, saving space,
“Second, we have to satisfy consumers,” he said. “That means we have to preserve flavor,
texture, color and cooking quality.”
During the industry-scale research, Atungulu said, he will be working on optimizing
the system to meet those industry and consumer requirements.
His research so far has identified 915 MHz as an efficient frequency to meet his goals.
But on a large scale, Atungulu said, that may not be the ideal frequency for all rice
“Some frequencies may not penetrate fully into some varieties,” he said. “We may also
have to adjust how the microwave energy is delivered. Perhaps some components will
have to be designed to control how the energy diffuses into the rice.
“These are the things we’ll have to play around with to find the optimal design and
control for commercial microwave rice drying,” Atungulu said.
Existing multiple-pass crossflow column dryers may be less efficient than microwaves,
but Atungulu says they have a proven track record. They are also durable, continuing
to work for decades with regular upkeep.
Rice processors will not be easily convinced to convert their drying systems. An essential
goal of the proof-of-concept stage of his research, Atungulu said, is to demonstrate,
with conclusive data, the economic benefits of microwave rice drying.
“We understand the feasibility of microwave drying,” Atungulu said. “We also want
to be able to articulate the merits of the system.”
Even with convincing data, Atungulu expects conversion will not happen overnight.
“It’s more likely to happen in stages,” he said. Given the durability of existing
rice dryers, that may take considerable time.
To learn more about Division of Agriculture research, visit the Arkansas Agricultural
Experiment Station website: https://aaes.uark.edu. Follow us on Twitter at @ArkAgResearch and Instagram at ArkAgResearch.
About the Division of Agriculture
The University of Arkansas System Division of Agriculture’s mission is to strengthen
agriculture, communities, and families by connecting trusted research to the adoption
of best practices. Through the Agricultural Experiment Station and the Cooperative
Extension Service, the Division of Agriculture conducts research and extension work
within the nation’s historic land grant education system.
The Division of Agriculture is one of 20 entities within the University of Arkansas
System. It has offices in all 75 counties in Arkansas and faculty on five system campuses.
The University of Arkansas System Division of Agriculture offers all its Extension
and Research programs and services without regard to race, color, sex, gender identity,
sexual orientation, national origin, religion, age, disability, marital or veteran
status, genetic information, or any other legally protected status, and is an Affirmative
Action/Equal Opportunity Employer.
Media Contact: Fred MillerU of A System Division of AgricultureArkansas Agricultural Experiment Station(479) firstname.lastname@example.org