Improvement of Rice Sample
Milling - 2005



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Project Leader and Principal UC Investigators

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




This project continues to look for ways to improve the consistency and accuracy of rice sample quality appraisals. The concern is that temperatures in quality appraisal millings are significantly higher than in commercial mills, negatively affecting the perception of rice quality and ultimately costing growers money.

The high temperatures of milled rice in the sampling process need to be reduced to room temperature before quality evaluations are conducted. However, the cooling process itself may also affect quality from moisture loss and fissuring. Research in 2005 had three main objectives:

  • Determine the effects of milled rice temperature on quality evaluation resultsó fissuring, total yield and head rice yield
  • Study the fissuring rate and moisture loss of milled rice with different cooling procedures
  • Develop recommendations for post-milling handling procedures

In this research, commercially obtained M-202 was milled under four conditions following standard Western operating procedures (i.e. with a 10-pound weight for milling and a 2-pound weight for polishing). The four milling conditions included normal milling; milling at high temperature; milling with cooling using ice water; and milling with cooling using room temperature water.

Total rice yield and head rice yield did not change much under different milling conditions, except for lowered head rice yields at high milling temperatures. This was different from previous research that showed total and head rice yields varied significantly with the milling conditions.

The results did show that the temperature of milled rice samples could be directly related to the fissure rates of whole rice kernels, especially at high temperatures. Cooling prior to milling significantly lowered the fissuring rate. Post-milling cooling did not show any significant effect on fissuring rates.

It was also determined that about 2.5 percent rough rice sample weight was lost during milling, probably due to moisture evaporation. Evaporation might be reduced with further reductions in sample milling temperatures. It would be useful to know how much moisture loss occurs in commercial milling.

Based on the results obtained from this study, the current post-cooling procedures with closed containers are more appropriate than the open container and open pan cooling methods used in other parts of the country. Different post-milling cooling temperatures may only affect cooling rates and not necessarily quality results. Since low milling temperature reduced the fissuring rate in milled rice, it is recommended that this approach be used in rice sample milling.


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