Milling Quality of Rice: Cylinder Speed vs. Grain-Moisture Content at Harvest
Milling quality of rice (Oryza sativa L.) or the percentage of head rice, broken kernels, and total (whole and broken kernels combined) is important economically to the U.S. rice producer. Eleven cultivars were harvested on 10 dates each in 1985 and 1986 and the percentage of broken rice kernels was determined after threshing the grain at cylinder speeds of 600 and 1000 revolutions per minute (rpm). The grain moisture contents ranged from 120 to 260 g/kg. Significant differences in milling yield occurred among cuitivars, cylinder speeds, and grain moisture contents. For example, ‘Newbonnet’ had the fewest broken kernels while ‘Leah’ had the most broken kernels. ‘Lemont’ produced the highest total milling yield; whereas, ‘L202’ produced the lowest total milling yield. Newbonnet produced the highest and Leah produced the lowest head rice yield. Percentage of broken kernels approximately doubled when the cylinder speed was increased from 600 to 1000 rpm. However, more mature kernels remained attached to the stalk at the lower cylinder speed. Generally, the percentage of broken kernels increased and head rice yield decreased significantly as the moisture content of the grain at harvest decreased.
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