Cleaning and grading

The purpose of cleaning the seed is to:

• Remove impurities such as trash, leaves, broken seeds, sand or grit, etc.

• Remove weed seeds or those of other plant species.

• Remove immature, shriveled, unfilled, and empty spikelets.

• Seed can be cleaned manually by winnowing. Winnowing removes only light, chaffy material.

• An air screen machine not only cleans the seed but separates seed of uniform size from oversize and undersize seeds. The process of separating seeds of uniform size is known as grading.

• Air screen machines are normally too expensive for on-farm ownership. Cleaning and grading are usually done by public or private seed agencies that contract with seed growers for hybrid seed production.