Grain cleaning is the process of removing impurities and foreign materials from harvested grains, such as wheat, corn, and rice. This ensures that the grains are safe for consumption and suitable for storage. Common impurities include dirt, stones, and plant debris, which can affect the quality and market value of the grain. The cleaning process typically involves several steps, including screening, air blowing, and gravity separation. Screening uses screens with different-sized holes to separate larger debris, while air blowing removes lighter materials. Gravity separation takes advantage of weight differences to further purify the grain, resulting in cleaner and higher-quality products.