Winnowing

Winnowing is the agricultural process of separating lighter chaff from heavier grains using air currents. The technique depends on the difference in density and momentum between the seed and its husk. The term originates from the influence of wind on the separation, with the wind helping to carry away the lighter material.

Traditionally, after threshing, the mixture of grain and chaff is tossed into the air using a winnowing basket or shallow tray. In a light breeze, the lighter chaff is blown or carried away while the heavier kernels fall back into a pile or onto a receptacle. Winnowing is commonly performed outdoors on a raised threshing floor, where a steady wind can improve efficiency.

Common implements include a winnowing basket or fan, which allows the farmer to fling the mixture upward and tilt or swing the vessel to create a breeze. The process can be done by hand, or with simple devices designed to maximize separation by catching the falling grain while the chaff is dispersed by the air.

In modern agriculture, winnowing is part of the cleaning stage in combine harvesters and other threshing machines. These machines use controlled air blasts and sieves to separate material by density and size, producing cleaner grain efficiently on a larger scale. Winnowing remains a fundamental concept in post-threshing grain cleaning and is also used in other contexts to separate fine particles from coarser ones using air flow.