September 20, 2021

Post-harvest technology: Cleaning rice

Harvested at 18 – 25% moisture, rice is mechanically dried to less than 15% moisture on the farm, at a commercial dryer, or at the mill before storage or processing.

Several stages of post-harvest handling of rice grains include field-drying, threshing, shed drying, cleaning, grading, storing, weighing, and milling before making it fit for human consumption. These can be done individually or a combine harvester can be used to perform the operations simultaneously.

The paddy rice from the warehouse or store must be dry cleaned to remove pieces of straws, stones and other foreign materials before processing.

High percentage of chaff, foreign matters include the soil piece, sand, small stones, metal debris, plastic or paper pieces, twig and branches, wood piece, weed seed, other grains, chemical and poisonous matters, etc., will unnecessarily increase the number of sack of rice and weight of paddy, which may cost the grower avoidable transport fees and milling fees paid the mill operator; and for the rice mill operator the cost of wear-and-tear and spoilage to his machine.

Most cleaners separate three groups of materials:
• The first separation is done by scalping or removing the objects that are larger than the grain. Either a flat oscillating screen or a rotary drum screen that allows the grain to pass through but retains straw can do this.
• The second separation retains the grains but allows broken grains, small stones and weed seeds to pass through. An air aspirator may also be incorporated to remove the dust and the light empty grains
Post-harvest technology: Cleaning rice

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