The ultimate goal of this research project was to develop a new milling procedure for improving the consistency and accuracy of rice sample milling.  Application of research results should save growers money currently lost to variations in milling yield in the rice sampling process.

Rice is sold on the basis of its milling quality, which is based on appraisal results of small rice samples.  The standard industry procedure and equipment used in these appraisals were developed more than 50 years ago and have not changed substantially since that time.

One of the major concerns about standard milling equipment is heat accumulation during milling, which results in high milling temperature and low milling quality or yield.  However, commercial millers have updated technology and it is believed that the commercial milling temperatures are lower than the lab where appraisals are conducted.  To assess the impact of current milling standards on appraisal results, it is important to determine the relationship between milling temperature and rice quality.

In this research, two selected low and high-quality M-202 samples were used and milled with standard milling pressure and time at the state laboratory operated by the California Department of Food and Agriculture.  To study the effect of milling temperature on milled rice quality, six rice samples were milled sequentially without cooling the mill between samples.  Researchers observed that the milling temperature continually increased as the milling process proceeded.  The temperature of milled rice increased substantially, with a corresponding reduction in head rice yield in the range of 2.8 percent to 3.8 percent.  Moisture loss caused by the increased temperature accounted for 82 percent of the total rice reduction.

Use of a heat exchanger developed at UC Davis improved total and head rice yields by cooling the milling process.  The cooling improved not only the yield but also the whiteness of milled rice, especially for low quality rice.  An infrared temperature sensor also showed promise as a tool to monitor milling temperature to achieve consistent results.

Based on the these encouraging results, further research will seek to improve the performance of the heat exchanger and to quantify effects of milling room temperature and pressure and time of milling on quality.  This research will lead to consistent results in rice sample milling by providing guidelines to modify current milling procedures and equipment.