Improvement of Consistency and
Accuracy in Rice Sample Milling-03



Home.gif (3162 bytes)

Next.gif (3180 bytes)

Back.gif (3162 bytes)

Project Leader and Principal UC Investigators

Zhongli (John) Pan, USAD/ARS, Albany, CA


The goal of this research project is to develop new milling methods and procedures that improve the consistency and accuracy of rice sample milling. Since the commercial rice milling industry updated its technology, a concern exists that lower milling temperatures could adversely affect initial rice quality appraisals. Furthermore, two distinct rice sample milling standards are in use in the United States-one in the South and one in California. These variations in existing protocols are costing growers money. Thus, specific objectives for last year's work were to:
  • Develop an efficient laboratory cooling method utilizing a modified cutting bar
  • Study quality characteristics of milled rice with different cooling methods
  • Investigate the effects of milling pressure and time on the quality of milled rice

Quality appraisals start with a laboratory mill analysis. A new internal heat exchanger with a modified standard cutting bar proved extremely effective in removing heat prior to and during milling, taking seconds to lower cutting bar temperature rather than 10 minutes with the traditional air-cooled approach. The internal heat exchanger and an external heat exchanger were used to study the effects of cooling methods on the quality of milled rice.

Two different M-202 rice samples with moisture content in the 12 percent range were obtained from Farmer's Rice Cooperative for use in this study. The samples were milled under various conditions with and without cooling at a laboratory operated by the California Department of Food and Agriculture.

Results showed that for high-quality paddy rice, cooling improved head rice yield by 1.6 percent, while whole kernel percentage improved by 5.7 percent. Researchers expect the improvement will be even more pronounced with low quality rice.

To study the effects of milling conditions on the quality of milled rice, researchers examined four variables - milling time and weight, and polishing time and weight. California procedures use 30 seconds for milling, 30 seconds for polishing and 10 pounds and two pounds for milling and polishing, respectively. The Southern protocol uses the same time periods but different weights-seven pounds for milling and zero pounds for polishing.

Results show significant relationships among milling temperature, total rice yield, head rice yield and whiteness. Over-milling could result in an increase of whiteness and milling temperature but may also significantly decrease total and head rice yields. The head rice yield obtained with California procedures was 2.6 percent lower than the head rice yield obtained with Southern procedures. The rice produced with California procedures was also significantly whiter. But there is no quantitative standard from the Federal Grain Inspection Service that can be used to determine whether rice has been over-milled with current California procedures. Future research should focus on whiteness or degree of milling in the commercial rice industry to establish a standard reference for rice sample milling.


Home.gif (3162 bytes)Next.gif (3180 bytes)Back.gif (3162 bytes)