WINNOWING (זָרָה, H2430, διασκορπίζω, G1399, scatter, fan, winnow) is the process of blowing the chaff from grain by wind or a forced current of air. This was done in the open on a flat surface of rock or ground, about forty or fifty ft. in diameter, preferably on the top of a hill. The winnowing was done after the threshing was completed. The threshed grain was usually winnowed in the evening, when there was likely to be a wind. It was thrown into the air by means of a six-pronged fork, called in KJV a fan (Isa 30:24). The chaff would be blown away, while the grain, being heavier, would fall to the ground. If there was no wind, one man waved a large fan, while another tossed the grain into the air with a fork. After the winnowing was completed, the owner of the grain and his family would generally spend the night with the grain to prevent stealing. The grain was finally passed through a sieve to remove the dirt, and then placed in jars for future use.
International Standard Bible Encyclopedia (1915)