 The straw was removed from the pile and the remaining grain and chaff was collected.By a process called winnowing, the grain was tossed into the air to allow the chaff and dirt to be blown away, leaving only the grain.Evidence of the use of threshing stones in various forms date from the Roman era, but eventually it became the method of threshing grain by the Molotschna Mennonite farmers in the Ukraine from about 1840 to 1900.