Cleaning is the process to remove rice straw chaff, foreign matters and immature/empty grains within paddy after threshing and drying. 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.
The importance of cleaning is as follows:
– To remove foreign matter, broken and immature grains to gain high milling recovery rate [to reduce broken rice amount].
– To increase the milling efficiency [to reduce fuel consumption].
– To decrease the damage of machine.
– To decrease running cost due to less wear of consumable parts.
– To increase more than 5% of mechanical efficiency and energy consumption if percentage of foreign matter, broken and immature grains is less than 1%.
– To decrease post-harvest loss.
Prevent broken rice. 5% broken rice decrease 10% on milling recovery.
The immature grains are classified into impurity. Immature grains decrease the milling recovery rate and the mechanical efficiency of the rice milling unit and is the cause of broken rice grains.
Use winnowing tray/ basket and mechanical cleaners such as manual winnower, oscillating sieves and aspirator. Small stone and sand that cannot be removed by winnowing can be removed hand picking.