Grains arriving in the mill usually contain foreign matter, such as strings, straw, parts of bags, wood, stones, or metal that must be removed before processing. The contaminants usually become mixed with the grains in the field and during its transfer through the various stages of the grain processing and grain-handling system. In addition, grains always contain some seeds of other plants, even if grown under the best conditions. If farming or environment conditions are poor, the amount of screenings is likely to increase. Although part of the foreign material (dockage), or all of it, is discounted in the trade, the cleaning system in the mill should be designed to allow the miller enough flexibility to properly clean any Grains arriving at the mill.

Grains arriving in the mill usually contain foreign matter, such as strings, straw, parts of bags, wood, stones, or metal that must be removed before processing. The contaminants usually become mixed with the grains in the field and during its transfer through the various stages of the grain processing and grain-handling system. In addition, grains always contain some seeds of other plants, even if grown under the best conditions. If farming or environment conditions are poor, the amount of screenings is likely to increase. Although part of the foreign material (dockage), or all of it, is discounted in the trade, the cleaning system in the mill should be designed to allow the miller enough flexibility to properly clean any Grains arriving at the mill.