Rice Utilization & Product Development - 2010

 

 

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Project Leader and Principal  Investigators

Zhongli Pan, research engineer, USDA-ARS, Dept of biological & Ag Engineering, UC Davis

 

 

 

This continuing rice utilization project focused on a new area in 2010—the formula or “shrink chart” used at rice dryers to assess crop quality and, consequently, payment to growers.

Rice is harvested at moisture levels that require drying for safe storage. Moisture removal reduces rice weight. Additionally, material other than grains is in harvested rice. To account for these factors, the final dried weight is docked. The standard dockage figure is 2% but is based on calculations that may be outdated. This project took a fresh look at the factors causing loss during drying to update the shrink chart. Even a 1% error in the shrink chart could have significant economic consequences for growers.

In this research, 51 medium grain rice samples were taken from three different dryers located in Colusa, Butte, and Yolo counties on five different days during the 2010 harvest. Harvest moistures ranged from 14% to 26%. A mechanical dockage tester separated grains, chaff, and other foreign material for freshly harvested rough rice samples and for dried rough rice samples. Scientists also performed “dropping tests” in which rice was allowed to free fall from 15 feet multiple times.

Dockage of freshly harvested rice samples varied between 0.2% and 2.0%, averaging 0.87%. No significant differences were noted among test varieties M-104, M-202, M-205, and M-206. Harvest moistures and geographic location of the rice also had an insignificant impact on dockage. Dockage was higher in early weeks of harvest than later in the season.

Scientists also observed that during drying, rice grains and nongrain material dry differently. Larger materials like chaff lose more moisture than grains. Average docking of dried samples was 0.71%, which was 0.16% lower than freshly harvested rice samples.

In the dropping test, as one might expect, some larger particles broke from the impact of freefall. This was evident as the proportion of fine material collected from a tray increased. Yet the overall impact from dropping was relatively small—0.03%.

Based upon findings from this research, the average value of dockage was 0.87%, significantly lower than the widely accepted 2% value. Shrink charts could be updated with this value. However, other factors such as rainfall and wind may ultimately affect dockage values. Therefore, dockage tests for rice samples on a larger scale should be conducted before making industry-wide recommendations.

 

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