Improvement of Rice
Sample Milling - 2007



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Project Leader and Principal  Investigators

Zhongli Pan, research engineer, USDA-ARS, Albany, CA




To improve the consistency and accuracy of rice sample quality appraisals, this project researches improvements to standard rice sample preparation procedures. Objectives for 2007 research included (1) the effects of rice sample preparation procedures on milling quality appraisal and (2) the development of quick rice sample preparation with infrared drying.

Rice samples with original moisture contents of 21.9% (low) and 25.6% (high) were dried to 14 percent moisture content with air at three different temperatures (73.4, 96.8, and 109.4 degrees Fahrenheit). Rice samples dried at the higher two temperatures were allowed to temper at ambient temperature for four hours. Additionally, the 109.4 degree sample was tempered in an incubator. Dried samples were stored in plastic bags to prevent moisture absorption during storage. Rice samples were milled with the new standard procedures at one, two, three, four and 14 days after drying to determine the effects of storage time on moisture and quality.

Rice dried at 109.4 degrees, followed by heated tempering, had higher milling quality compared to the other drying and tempering combinations. Maximum head rice yield values were achieved when rice was milled two days after drying. The whiteness of rice samples dried with ambient air was slightly higher than the other drying and tempering procedure but not to a significant extent. These findings suggest rice should be stored at least two days to improve appraised milling quality.

The second objective in 2007 research was to determine a quick rice-sample preparation procedure with infrared drying. Rice samples with initial moisture contents of 21.9% and 25.6% were dried as a single layer for one, two, and three drying passes with infrared heating. Samples were heated for about one minute to about 140 degrees F and then allowed to cool for about two hours. They were then dried to 14 percent moisture content with ambient air.

Milling quality was not affected for the lower moisture rice with two drying passes or with three passes in the higher moisture rice. Moisture content after infrared drying was close to the 14 percent required for rice milling. The results indicate that rice milling samples can be prepared with infrared drying with much reduced drying time.


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