Threshing Threshing White-le-Head Category="Agriculture"Threshing is the process of beating Cereal plants in order to separate the seeds or grains from the Straw. Although once done by hand using a flail, this tiring task is now mostly done by Machine. Threshing is one of the many tasks a Combine harvester performs, along with harvesting the plant and cleaning the grains. In some places, it is common to see plants spread along the surface of country roads so the grain may be threshed by the wheels of passing vehicles.