There are two similies: "like a whirlwind" and "like the chaff of the summer threshing floor".
Chaff.
In biblical times, wheat separation was normally performed by hand. The workers would beat on the harvested wheat with sticks, branches, or a similar tool, then throw it into the air on a windy day to allow the chaff (outer hulls) to blow away.
Tonight we are winnowing barley on the threshing-floor.
Naomi
Threshing: it is done by beating the sheaves against the wooden bars to separate the grains from the stalks. Winnowing: it is the process of removing the unwanted husk from the grains. It is done by pouring the grains from a height on a windy day when the grains fall on the ground and the chaff is blown away.
For grain, they are called "harvesters" or combine harvesters, which is a huge machine that gathers the crop (be it corn, wheat, barley, oats, etc.) and goes through the process in the machine of separating the kernels or seeds from the rest of the plant. What's left over is ejected as chaff, which can be baled for straw. In the old days, threshing machines were used to separate seeds of grain from the chaff.
Chaff is a mass noun. It has no plural.
Threshing was done by beating the grain using a flail on a threshing floor or by making donkeys or oxen walk in circles on the grain on a hard surface. A flail is a tool used for threshing. It is made from two or more large sticks attached by a short chain; one stick is held and swung, causing the other to strike a pile of grain, loosening the husks.
It measns that king David bought a threshing floor for 50 shekels of silver and then built an altar there.
Many different tools were used by peasant farming labourers, including the threshing flail. Threshing was an extremely lengthy and hard manual job during the winter months, part of the sequence of processes the grain had to go through before it was taken to the miller. Wheat and other grain crops were stored in a barn after the harvest, still tied in sheaves. Ploughing and sowing the next crop was the priority while the weather was still reasonable; threshing often took place in the depths of winter when working the land was impossible. Teams of men and boys would take rakes and flails to the barn. The work was so hot that they often stripped to their braies (underwear). The boys would spread out some of the crop on the floor and the men would work together to thresh or "thrash" it with their flails - knocking out the important kernels of wheat along with the chaff. The boys would then rake away all the straw before spreading out more of the crop - the women would sweep up the wheat and chaff into winnowing baskets for the next part of the process, which had to be done outside in a breeze. The threshing flail in England traditionally had an ashwood handle and a blackthorn "beater", hinged together with leather straps or metal rings. See links below for images of the threshing flail:
Chaff on the Wind was created in 1986.