National Agricultural Research Institute Copies of this leaflet can be obtained from: The Publications Section National Agricultural Research Institute Wet Lowlands Mainland Programme PO Box 1639 LAE 411 Morobe Province Telephone: (675) 475 1033/475 1228 Facsimile: (675) 475 1034 Email: nariwll@datec.net.pg Cleaning and Winnowing of Rice NARI TOKTOK RGP006 April 2003
Cleaning and Winnowing of Rice Introduction Improper cleaning usually result in grain loss and lower head rice recovery in mills. Cleaning helps to reduce bulkiness during subsequent post harvest operations. Acknowledgement Our thanks and gratitude to Carolyn Pia afu and Kathleen Terrence, both of the PNG University of Technology, Lae for help received. We acknowledge IRRI, Philippines for pictures on pages 7 and 8 of this publication. You should remove straw pieces, unfilled grains and other foreign materials. Cleaning and winnowing can be done manually, using wind energy or with the use of machines. You can use traditional winnowers like the winnowing basket and wooden boxes with perforations. Disadvantages of inadequate cleaning If you do not clean your rice properly, you may face problems. Rice with impurities will: deteriorate during storage reduce head rice yield damage your milling machine increase weight and bulkiness during handling Compiled by Joel Waramboi Rice and Grain Programme April 2003 2 11
Method 1: Air cleaning using wind If you live in areas where there is high air velocity, air-cleaning will be most appropriate for you. You can also use electric fans to provide air for winnowing. Follow the steps below. Step 1. Layout a canvas Spread out a canvas on a flat surface to work on. You also use plastic and visqueen materials. Do not use materials that have rough surfaces on them. 10 3
Step 2. Put seeds into a suitable container You can use a normal bucket if you wish. Make sure it is not too heavy for easy handling. Step 3. Position your stand Stand at right angles (90 ) from the direction of the wind. Step 4. Pour the grains Pour the grains slowly against the wind. The wind will blow away the rubbish and empty grains from the good seeds. Repeat this process 2-3 times to properly clean the seed. 4 9
Step 5. Handling cleaned paddy Collect your cleaned seeds and store them safely in a clean and dry area. Remove any dirt, rubbish or food remains in the storage shed. Stack the bags properly. Source: IRRI Rice Knowledge bank CD Seed grading If you intend to use the seeds for commercial purposes, you may need to grade them. The grains should have uniform size and weight. In commercial operations, mechanical graders, gravity tables, rotary screens, indented cylinders and lenght graders are available for this purpose. Seed purity You should maintain seed purity at all times. You should handle them separately right from the field through to cleaning, milling, cooking and consumption. Do not mix varieties. 8 If you have washed or sprayed the storage shed with chemicals, make sure it is properly dried before storage. These chemicals can damage your cleaned seeds. 5
Related seed cleaning activities Cleaning removes unwanted materials like straws, chaff, weed seeds, soil particles and rubbish from the grain. It improves grain storability, reduces dockage during milling, gives good quality milled rice and improves the milling output. It also reduces insects, pests and disease infestation. Winnowing Removes lighter materials such as unfilled grains, chaff, weed seeds and straw remains. This is done by using a blower, air fan or by wind. Recover only the heavier, healthy and good quality grains after winnowing. Screening/Sifting Sifting removes smaller size materials like weed seeds, soil particles and stones. Sieve the paddy through smaller size screens of 1.4mm or less for effective cleaning. Seed cleaning Visually inspect the paddy and remove deformed, discolored, germinated, broken or mouldy seeds. They can reduce grain quality, viability and vigor of the seed. For good winnowing results, follow these recommended practices: Place the grain on a winnowing tray Place a net, mat or canvas on the ground Tilt the tray against the wind Pour grains slowly at a height of 1m Separate only light from heavy grains Recover only the heavier grains Use a fan if there is not enough wind 6 Source: IRRI Rice Knowledge bank CD If you do not take appropriate care, seeds can also be fermented, leading to yellowish grains. This happens when heat and micro-organisms built-up. You should also remove fermented seeds. 7