It is the basic machine in the wheat cleaning plant. It removes the impurities on the basis of three physical properties- size, shape, and density. The typical air-screen cleaner consist of a four-screen machine located beneath a seed hopper, it is widely found in a farm seed-cleaning plant.The purpose of flour milling is to provide a fit for purpose, high quality flour which is free from contaminants and not tainted in any way. To achieve this the miller must ensure that any foreign contaminants are removed prior to commencing the milling process.