For the purposes of classification and commercialization, the maximum index of impurities allowed in the grain mass is 3%, established in the classification ordinances. However, the ideal storage condition is the total exemption of impurities, as they constitute an appropriate habitat for the development of insect pests, mites, bacteria, and fungi.
During loading, they accumulate in the center and walls of the silos or in the back of the “V” bulk carriers. A recommended practice for the partial solution of this problem is the removal of part of the load, from the bottom to the top of the grain mass, with the removal of a layer of approximately 5 mm thickness, removing all concentrated impurity and distributing it, superficially, in the product mass. In the case of vertical silos, the center (“tube of impurities “) should be removed.
The concentration of impurities at specific points of the mass impairs the distribution of air during aeration, which usually translates into increased temperature, and a degradation of quality, or a total loss of the product.
The most suitable solution for reducing the content of impurities is the installation of a cleaning machine after the drying system, allowing the operation called post-cleaning.