Separate the chaff from the grain

verb

1. To treat (something, such as grain) by exposure to a current of air so that waste matter is eliminated
2. To free of unwanted or inferior elements pare
3. Narrow, reduce

   "winnowed the field to four contenders"

4. To blow on fan

   "the wind winnowing his thin white hair"

5. To separate chaff from grain by fanning
6. To separate desirable and undesirable elements

noun

1. A device for winnowing
2. The action of winnowing
3. A motion resembling that of winnowing