Easton's Bible Dictionary: M. G. Easton, M.A., D.D.

Winnow

Corn was winnowed,

  1. By being thrown up by a shovel against the wind. As a rule this was done in the evening or during the night, when the west wind from the sea was blowing, which was a moderate breeze and fitted for the purpose. The north wind was too strong, and the east wind came in gusts.
  2. By the use of a fan or van, by which the chaff was blown away (Ruth 3:2; Isa. 30:24; Jer. 4:11,12; Mt. 3:12).

Original from The Bible Foundation - bf.org. They claim public domain status for their original text.