In an effort to improve the consistency and accuracy of rice sample quality appraisals, this project is examining the development of standard rice sample preparation procedures. Research in 2006 focused on how different milling procedures and storage times affect rice quality, an especially important consideration during quality appraisals.

Commercially obtained rough M-202 rice with harvest moisture at three levels – 24.8%, 22.7% and 20.2% – were dried at four temperatures ranging from 73.4 to 127.4 degrees Fahrenheit to create rice samples with different milling quality. High-temperature drying resulted in significantly lower milling quality than low-temperature drying.

The rice samples with different quality were milled with three different procedures – Western milling, Western milling with low-temperature cooling, and Southern milling procedures. The low-temperature procedure is a water-cooled system developed in the previous year’s research. It had the best head rice yield, followed by the Southern procedure. The differences over standard Western milling practices were significant – a 3% to 4% improvement for the cooled procedure and a 1.5% to 2% improvement for the Southern procedure.

HRY improvement with low temperature and Southern milling procedures compared to Western milling procedures

Results are similar to findings from the previous two years. More importantly, low-temperature milling improved appraised rice milling quality about 1% more on average for low quality rice compared to high quality rice. This shows that low-temperature milling is a potentially viable approach for both appraisal sampling and commercial rice milling.

After three years of testing, it is recommended that milling procedures in the United States be standardized using low temperature or controlled milling temperatures in rice sample milling.

Rice sample preparation procedures and their affect on appraised milling quality were also studied. Rice at two moisture contents – 25.1% and 20.5% – were dried under three different procedures. The standard drying procedure is 30 minutes at 109.4 degrees Fahrenheit, followed by four hours tempering for each drying pass. Rice was also dried with ambient air, both with and without tempering.

Tempering removed 2% moisture in each drying pass. The one without tempering dried from the original moisture content to 14% in a single pass. Appraised milling quality results showed that the standard drying procedure has up to 8% lower head rice yield than ambient air drying, which was unexpectedly high and needs to be studied further.

Dried rice milled one day after drying had about 2% lower head rice yield compared to samples stored four days or more. Further study of how tempering affects head rice yield in high moisture rice is needed.