Improvement of Rice
Sample Milling-04



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Project Leader and Principal UC Investigators

Zhongli (John) Pan, research engineer, USDA/ARS, Albany, CA


The ultimate goal of this research is to develop new milling methods and procedures that improve the consistency and accuracy of rice sample milling.  Research results and recommendations for industry changes described below should minimize California rice producers’ economic loss caused by variation in milling. Specific objectives for 2004 work were to:

  • Determine the effects of different cooling methods on quality appraisal results

  • Compare quality appraisal results obtained with standard Western and Southern milling procedures

  • Develop recommendations for modifying current rice sample milling procedures

Commercial rice mills have updated milling technology and equipment.  These improvements have lowered mill temperatures below those of laboratory mills used in quality appraisals.  Furthermore, two different rice sample milling standards have evolved in the United States — one in use in Southern rice growing states, the other in California. 

In 2004, medium grain rice samples (M-202) from California and the South were milled using respective rice sample milling procedures.  Varying rice samples reflected low, medium and high quality. The samples were milled under various conditions with and without cooling at a laboratory operated by the California Department of Food and Agriculture.  Both Western and Southern procedures were used. 

CDFA’s current milling practice is to air cool a cutter bar before a new rice sample is milled.  To reduce the milling temperature during milling, two external and internal cooling devices were previously developed by researchers.  They used both ice water and room temperature water to cool the heat exchangers.  In general, head rice yield and total rice yield improved with increasing cooling.  These results suggest that sample milling with cooling can reduce the milling quality loss in quality appraisal caused by high milling temperature.

Western milling procedures use a 10-pound weight for milling and a two-pound weight for polishing.  Southern milling procedures use a seven-pound weight for milling and no weight for polishing.  Researchers found that the Southern milling procedure resulted in about 2-3 percent more head rice yield than Western milling procedures.

Based on these results, the California rice industry should consider the following three options to improve milling consistency and accuracy of rice sample milling:

  • Replace Western milling procedures with lighter-weight Southern milling procedures.

  • Employ internal and external heat, water-cooled heat exchangers to improve quality appraisal results and to increase processing efficiency.

  • Use of ice water in heat exchanger significantly shortens cooling time between samples, but the additional refrigeration equipment necessary to provide low-temperature water may make ambient temperature water a more attractive option.


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