English: Chaff swirling through the air. The straw emerges from the rear of the combine harvester in a continuous flow; a profusion of chaff can be seen swirling through the air in its wake. Baling the straw will be next. – A combine harvester is a machine that combines the harvesting, threshing and cleaning of grain crops. They have so-called headers which cut the crop and feed it into the threshing cylinder consisting of a rotating drum that separates the grains and chaff from the straw. The grain heads fall into sieves whereas the straw is carried on to the rear on so-called straw walkers, which also have holes in them, allowing for any remaining grain to drop into the sieves. Having reached the end of the walkers the straw falls out of the rear of the machine.