EFFECTS OF MCGILL NO 2 MILLER SETTINGS ON SURFACE FAT CONCENTRATION OF HEAD RICE

The surface fat concentration of 384 head rice samples milled with a M cGill No. 2 miller was measured with a Goldfisch lipid extractor (Labc onco, Kansas City, MO). The data were used to evaluate the effects of moisture content, milling time, pressure applied to the rice, and init ial rough rice weight on the degree of milling of two varieties of lon g-grain rice. Moisture contents ranged from 9 to 14% wet basis; millin g time ranged from 15 to 60 sec in 15-sec intervals; and initial rough rice weights were 125 and 150 g. The pressure applied to the rice dur ing milling was adjusted by the position of a 1.5-kg weight on the lev er arm and ranged from 6 to 18 cm, in 6-cm increments. Moisture conten t and milling time were found to be the most significant variables aff ecting surface fat concentration. Sample size was the least significan t variable. Surface fat concentration decreased as moisture content, p ressure applied to the rice, and milling time increased. It increased as sample size increased. A varietal difference in surface fat concent ration existed. An equation that predicts the surface fat concentratio n for the various experimental settings was developed. Head rice yield is directly related to surface fat concentration. Equations relating the two at different moisture contents were developed. Milling at lowe r moisture contents typically produced higher head rice yields, even w hen differences in surface fat concentration were taken into account.