Optimizing rice mill lab analysis can improve yield, consumer qualities

FAYETTEVILLE — Before it gets to your table in a steaming dish, rice has to go through the mill.
More specifically, the unprocessed rice kernels that are encased in an inedible hull must undergo milling to reveal the white rice grain. Along with even drying, proper milling of rice can increase the amount of rice that makes it from the farm to the kitchen by decreasing the number of broken kernels. Non-standardized milling impacts nutritional and functional qualities, sensory attributes and cooking performance.
One of the ways to improve rice milling starts in a rice processing lab, where rice from farms is evaluated for moisture content and other milling properties that inform the mill operators how to set their mills for the best performance, according to Griffiths Atungulu, a professor and agricultural engineer with the Arkansas Agricultural Experiment Station and Dale Bumpers College of Agricultural, Food and Life Sciences.
Atungulu recently published a study with members of his rice processing research team that offers information to help optimize lab methods for rice milling. The study, published in the Cereals & Grains Association journal Cereal Chemistry, is titled “Optimizing lab methods for consistent rice milling analysis.”
“Anytime we assess rice milling yields — especially head rice yield — we’re indirectly evaluating rice quality,” said Atungulu, who is also director of the Arkansas Rice Processing Program for the experiment station, the research arm of the University of Arkansas System Division of Agriculture. “This is because head rice yield is a primary indicator of and has some relationship with milled rice quality.
“Rice quality also includes factors such as nutritional value, functional performance in processed products, and sensory attributes — all of which matter greatly to the consumer,” he said.
Fewer broken kernels also result in better prices and more profitable crops for farmers.
Head rice yield is the percentage of unbroken rice kernels after milling and is part of the milling yield. Total milling yield is the amount of rice recovered, which includes broken kernels and head rice, which is the rice that is three-fourths of a kernel and above the length of the whole unbroken milled rice.
Complicating the matter for farmers and millers are periods of high nighttime temperatures during the summer months. Nighttime temperatures above 75 degrees are detrimental during rice’s grain fill phase because they can lead to chalkiness, thinner kernels and potentially lower milling yields. Thinner kernels are more prone to breaking in the milling process.

Spreading the word
Atungulu recently presented the research on optimizing lab methods to about 300 people in 17 countries through a Partners in Food Solutions webinar.
Partners in Food Solutions is an independent nonprofit organization that ​works to strengthen food security, improve nutrition and increase economic development across Africa by connecting expertise from global food companies and other organizations with promising entrepreneurs in 11 African countries to help expand and increase the competitiveness of the food processing sector, according to Nikki See, director of communications for Partners in Food Solutions.
Samuel Olaoni, a doctoral research student in the food science department and lead author of the study under Atungulu’s advisement, will also present the findings during the Arkansas Rice Processing Program Industry Alliance meeting, May 20-21, at the Don Tyson Center for Agricultural Sciences in Fayetteville.
A time of transition
Traditionally, rice processing labs have used the McGill No. 2 mill to assess rice milling performance per the recommendations of the U.S. Department of Agriculture’s Federal Grain Inspection Service, or FGIS. However, Olaoni’s study points out that the FGIS is phasing out the McGill No. 2, and there has been a need to recalibrate milling assessments for standardized milling evaluation across various labs.
The study showed there can be significant differences in milling yield and whiteness index between the McGill No. 2 and the two other lab mills tested — Satake and Zaccaria — based on the moisture content of the rice and the cultivar of rice that was milled. More research is needed, the study noted, to understand and optimize other modern laboratory mills.
Co-authors of the study include research associate Bindu Regonda and assistant professor Kaushik Luthra, both with the biological and agricultural engineering department. Regonda was previously a graduate student under Atungulu’s advisement.
The research was supported by Arkansas Rice Check-Off funds administered by the Arkansas Rice Research and Promotion Board. The authors acknowledge financial support from the corporate sponsors of the Arkansas Rice Processing Program, the U.S. Department of Agriculture National Institute of Food and Agriculture Hatch Act Funding, and the University of Arkansas System Division of Agriculture.