The final stage of growing wheat involves the harvest, which is the act of gathering the mature stalks from the field. Before this grain can be used for food, the edible kernel must be physically separated from the inedible parts of the plant, such as the straw and the seed head. This separation process prepares the grain for milling.
Defining the Threshing Process
Threshing refers specifically to the mechanical action of loosening the edible grain kernel from the inedible stalk and the protective outer layers known as chaff. The purpose of this step is to make the grain ready for subsequent processing, such as winnowing and milling for flour. Threshing is accomplished by applying a physical force, such as impact or friction, designed to break the natural bond between the seed and the plant head. This action must be forceful enough to release the kernel without damaging the grain itself.
Traditional Threshing Techniques
Before widespread mechanization, threshing was a highly labor-intensive and time-consuming task, often taking place on a prepared surface called a threshing floor. One early method involved treading, where harvested grain heads were spread out and people or animals, such as oxen or horses, walked repeatedly over the material. This continuous pressure and friction dislodged the kernels from their husks.
Another common method involved the use of a flail, a simple tool consisting of a long handle connected to a shorter, heavier wooden club. Workers would physically beat the bundles of wheat laid out on the floor, using the impact to knock the grain free. This technique was demanding, with one worker typically managing to thresh about 7 bushels of wheat per day.
Early stationary threshing machines also existed, which required manual feeding of the cut stalks into a mechanism. These machines used a rotating drum to beat the grain, but still relied heavily on human or animal power to operate.
Modern Mechanized Threshing
The invention of the combine harvester drastically changed the process by integrating the three separate tasks of reaping, threshing, and winnowing into a single, self-propelled machine. After the header cuts the crop and feeds it inward, the material is delivered to a central cylinder or rotor that rotates at high speed.
The cylinder is fitted with toothed or grooved bars that strike the wheat heads, creating the impact and friction necessary to separate the kernels from the stalks and chaff. This high-speed beating action effectively mimics the force of a flail but at a vastly increased scale and rate.
The newly threshed material, which is a mix of grain and debris, then passes over a concave, a perforated grate that surrounds the cylinder. The heavier grain kernels fall through the gaps in the concave and onto a set of sieves, while the straw and lighter material are carried through the machine for further separation and expulsion. This integrated system has increased the efficiency of harvesting, reducing the labor required and increasing the speed at which grain can be prepared for consumption.