Cleaning
Grain cleaning after harvest is important as it removes unwanted materials from the grain. Clean grain has a higher value than grain that is contaminated with straws, chaff, weed seeds, soil, rubbish, and other non-grain materials. Grain cleaning will improve the storability of grain, reduce dockage at time of milling, and improve milling output and quality. Seed cleaning will reduce damage by disease, and improve yields. Following are some general guidelines for cleaning grain and seed.
Winnowing. Lighter materials such as unfilled grains, chaff, weed seeds, and straw can be removed by from the grain by using a blower, air fan, or by wind. Recover only the heavier grains.
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)
Seed cleaning. Malformed, discolored, germinated, broken or moldy grains in seed lots can severely impact seed quality, viability and vigor. Visually inspect the seed prior to storage and consider removing these grains from the seed lot.
Seed grading. For commercial seed processing, seed grains should have uniform size and weight. A variety of commercial equipment can be used to achieve uniformity in seed size and shape. These include gravity tables, rotary screens, indented cylinders, and length graders.
Seed purity. Maintain seed purity by preventing mixing with other varieties, and contamination with other species.
Guidelines for good winnowing methods/recommended 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
