In the milling operation a thin layer of peat, approximately 15mm deep, is cut from the surface of the bog where it is left to air dry over a period of a few days. This layer of peat is called a crop. At this stage in the process, the water content of the crop after milling is about 80%. The miller itself consists of a number of rotating drums fitted with pins to cut the peat. It is towed and powered by an agricultural tractor.