U.S. farmers produce grain in a wide variety of geographical regions with major differences in soil, temperature and climate. However, the management tools they use to meet their goals of producing and harvesting a quality corn crop are similiar. Growing conditions, timing of harvest, handling equipment, storage practices and transportation procedures all affect grain quality. Finally, when it comes time for official grading, there are essential chemical and physical properties that influence the final grade assignment.
The U.S. grading system for corn takes into account many physical properties of the purchased lot. Initial classification is detemined by the color of the corn: yellow, white or mixed. Special grades can be assigned to corn including dent kernel, which has kernels with a distinct depression or dent in the crown; flint corn, which has a kernel with a rounded crown but is smaller than a dent kernel; infested corn, which indicates the presence of insects; and waxy corn, a starch variant of normal corn.
Additionally, grain quality grades reflect a range of properties that can be defined in terms of physical, sanitary and intrinsic quality characteristics.
Physical quality characteristics include moisture content, test weight, kernel size, total damaged kernels, heat damage, broken kernels, stress cracking and breakage susceptibility – which are results of handling, transporting and storing. These issues are unavoidable in a high volume grain handling system, but proper monitoring identifies problems, allows accurate grading, and minimizes the effect on the quality of corn export cargoes.
Sanitary characteristics include fungi and mycotoxin count, insects, rodent excrements, foreign material, toxic seeds, pesticide residue, odor and dust. These factors can also be minimized with steps taken before harvest to clean storage facilities and when corn is properly stored and monitored.
Intrinsic quality characteristics include milling yield, oil content, protein content, hardness, density, starch content, feed value, viability and storability. These factors depend on the variety of corn as well as environmental conditions from planting to harvest. These characteristics are genetic, cannot be altered, and in most cases have a positive impact on quality.
Graders use testing equipment that has a series of sieves to separate and catch broken kernels and foreign materials (BCFM). The machine removes larger and finer particulate matter from a sample to determine the percentage of BCFM. According to the Federal Grain Inspection Service (FGIS), damage is reported as a percentage and factored into the quality grade as described in the FGIS handbook, available at http://www.gipsa.usda.gov/fgis/public_handbooks.aspx.
Numerical grade designations, from U.S. No. 1 to U.S. No. 5, plus a U.S. sample grade that does not meet the requirements for a numerical grade, are assigned to all samples based on their tested characteristics. While a particular lot may grade higher than another, corn from multiple sources is typically blended together as it moves through the marketing channel. As a result, the grade for a given intrinsic quality characteristic is an average of multiple samples.
Carlos Campabadal, faculty member of the Department of Grain Science and Industry at Kansas State University and program specialist for the International Grains Program Institute (IGP), said despite the varied grade designations, international customers can expect the same quality from U.S. farmers throughout the year.
“We have well-established operation systems in place from the farm to export vessel,� he said. “Customers abroad can expect consistent quality from the United States.�
U.S. farmers make every effort to raise and market a top quality product for domestic and international customers. “We are always working to improve,� Campabadal said. “And we always deliver.�