Grain cleaning
Winnowing
Lighter materials such as unfilled grains, chaff, weed seeds, and straw is removed through winnowing. To improve efficiency when there is no sufficient wind, a blower or an air fan can be used. However, winnowing recovers only the heavier grains. Other heavy particles like heavier weed seeds, off types, stones and dirt might still be included in the rice.- Screening/Sifting
Smaller materials such as weed seeds, soil particles and stones can be removed by sieving the grain through a smaller sized screen (1.4 mm or less sieve opening). This can also be done mechanically through machine cleaners which use an air stream to remove light materials such as straw, chaff, and unfilled grains.
Recommended winnowing practices:
- Place grain on a winnowing tray.
- Place a net or mat on the ground.
- Tilt the tray against the wind.
- Pour grain slows at a height of about 1 m.
- Wind will separate light from heavy grains.
- Recover only the heavier grains.
- Repeat the procedure if needed.
- Use a fan or blower if there is not sufficient wind.