Boyd’s Bible Dictionary:
(wind). The process of winnowing or winding grain was that of tossing the mixed chaff and kernels into the air, on a high, windy spot, with a fork or shovel, so that the wind could carry the chaff away. The floor on which the kernels fell was usually clean and solid, and when not so, a sheet was used to catch the grains (Isa. 30:24; 41:16; Matt. 3:12). Evening was the favorite winnowing time because the breezes were then steadiest (Ruth 3:2).
“243. The Time for Winnowing” From Manners and Customs of the Bible:
Ruth 3:2. Behold, he winnoweth barley tonight in the threshing floor.
The evening was selected not only because it was cooler than the day, but because of the increase of wind which enabled the husbandman to winnow more thoroughly. For the Oriental mode of winnowing see note on Amos 9:9 (#609) and on Matthew 3:12 (#634).
“634. Winnowing Grain” From Manners and Customs of the Bible:
Matthew 3:12. Whose fan is in his hand, and he will thoroughly purge his floor, and gather his wheat into the garner; but he will burn up the chaff with unquenchable fire.
See also Luke 52:17.
The grain in the East is threshed in the open air (see note on Gen. 50:10, #90) by being trampled under the feet of oxen or horses (see note on Deut. 25:4) or by means of instruments, as described in the note on Isaiah 28:27-28 (#508). By these processes the straw becomes very much broken; and, to separate the grain from the hulls and straw the mingled mass is thrown against the wind by means of a wooden shovel, or else a wooden fork, having sometimes two prongs and sometimes three, and a handle three or four feet long. This is the “fan” alluded to in a number of Scripture passages. It is usually employed in the evening. See note on Ruth 3:2 (#243). The wind carries the chaff away, while the grain falls to the ground. The grain is sometimes sifted after the winnowing. See note on Amos 9:9 (#609). The chaff is burned and the grain is stored, either in subterranean granaries (see note on Jeremiah 41:8, #551) or in barns. See note on Genesis 41:48 (#80).
The fan is referred to in Isaiah 30:24, where it is mentioned in connection with the “shovel.” The precise difference between the two instruments there indicated is not now known. See also Jeremiah 4:11; 15:7; 51:2. The scattering of the chaff by the wind after fanning is frequently alluded to figuratively. See Job 21:18; Psalm 1:4; Isaiah 29:5;. 41:16; Daniel 2:35; Hosea 13:3.
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