Impact of the Corn Market Channel on Quality
While the U.S. corn industry strives to minimize the change in the physical and sanitary quality attributes as corn moves from the farm to export ports, there are stages of the system where these quality characteristics change. These changes are inevitable due to the biological nature of the grain and the physical handling and conditioning required to move corn from production areas to export ports. The following sections introduce these various activities within the U.S. corn marketing system to provide some insight on why corn quality may change as it moves from the field to the ocean vessel.
Drying and Conditioning
Farmers often harvest their corn at moisture contents ranging from 18 to 30%. This range of moisture content generally exceeds safe storage levels which usually vary from 14 to 17%. Thus, wet corn at harvest must be dried to a lower moisture content to be considered safe for storage and transport. Conditioning is the use of aeration fans to control temperatures and moisture contents which are both important to monitor for storage stability. Drying and conditioning may occur either on a farm or at a commercial facility. When corn is dried, it can be dried by systems using natural air, low-temperature, or hightemperature drying systems. The high-temperature drying methods will often create more stress cracks in the corn and ultimately lead to more breakage during handling than natural air or low-temperature drying methods. However, high temperature is the only option in some cases due to logistics.
Storage and Handling
In the U.S., the storage types in which corn is stored can be broadly categorized as upright metal bins, concrete silos, flat storage (buildings), or on-ground piles. Upright bins and concrete silos with fully perforated floors are the most easily managed storage types because they allow in-floor aeration ducts or on-floor air ducts to help maintain uniform airflow through the grain. Flat storage or on-ground piles can be used for short-term storage when harvest production is higher than normal and surplus storage is needed. However, it is more difficult to install aeration ducts in these types of storage, and they often do not provide uniform aeration. In addition, on-ground piles are sometimes not covered and may be subjected to weather elements that can result in mold damage.
Handling equipment can involve both vertical elevations by bucket elevator or horizontal conveying usually by belt or en-masse conveyors. Regardless of how the corn is handled, some corn breakage will occur. The rate of breakage will vary by types of equipment used, severity of the grain impacts, grain temperature and moisture content, and by corn quality factors such as stress cracks or hard endosperm. As breakage levels increase, more fines (broken pieces of corn) are created which lead to less uniformity in aeration and ultimately to higher risk for fungi and insect infestation.
Cleaning
Cleaning corn involves scalping or removing large non-corn material and sieving to remove small shriveled kernels, broken pieces of kernels, and fine materials. This process reduces the amount of broken kernels and foreign material found in the corn. The potential for breakage and initial percentages of broken kernels, along with the desired grade factor, dictate the amount of cleaning needed to meet contract specifications. Cleaning can occur at any stage of the market channel where cleaning equipment is available.
Transporting Corn
The U.S. grain transportation and distribution system is probably the most efficient one in the world. It begins with farmers typically transporting their corn from the field by either farm tractor wagons or trucks to on-farm storage or country elevators. Corn is then transported by truck and/or rail from country and inland subterminal elevators and by barge from river elevators to its next destination. Once at export ports, corn is loaded onto ocean-going vessels. As a result of this complex yet flexible marketing system, corn can be loaded and unloaded several times, increasing the amount of broken kernels, stress cracks and breakage.
Corn quality changes during shipment in much the same manner as it changes during storage. Causes of these changes include moisture variability (non-uniformity) and moisture migration due to temperature differences, high humidities and air temperatures, mold development, and insect invasion. However, there are some factors prevalent for grain transportation that make quality control during transport more difficult than in fixed storage facilities. First, there are few modes of transport equipped with aeration, and as a result, corrective actions for heating and moisture migration cannot be taken during transport. Another factor is the accumulation of fine material (spoutlines) near the center when loading barges and ocean vessels. This results in the whole kernels tending to roll to the sides, while fine material segregates in the center. A similar segregation occurs during the unloading process at each step along the way to final destination.
Implications on Quality
The intrinsic quality attributes such as protein cannot be altered within a corn kernel. However, as corn moves through the U.S. corn market channel, corn from multiple sources is mixed together. As a result, the average for the intrinsic quality is affected by the quality levels of the corn from the multiple sources. However, the above-described marketing and distribution activities inevitably alter the physical and sanitary quality characteristics. The attributes that can be affected include test weight, damaged kernels, broken kernels, kernel size, stress crack levels, moisture contents and variability, foreign material, and mycotoxin levels.