Even though drying conditions are excellent now, some producers may be faced with drying high-moisture or immature corn this fall. To minimize spoilage during drying, do not use natural air or low-temperature drying for corn with moisture contents of more than 21%, according to Ken Hellevang, North Dakota State University Extension Service grain drying expert. Natural air drying doesn't work well in late fall because the air's drying capacity is extremely poor at temperatures below about 35° F.
When outdoor temperatures average near or below freezing, Hellevang recommends cooling the corn to 20-25° F for storage this winter and finishing drying in early April. Natural air drying is the most energy- and cost-effective method of drying at that point.
Limit the corn depth to about 20-22 ft. to obtain the proper airflow rate for drying. An airflow rate of 1-1.25 cubic ft./minute (cfm)/bushel is necessary to dry the corn before deterioration occurs. Turn fans off during extended periods of rain, snow or fog to minimize the amount of moisture the fans pull into the bin.
Adding heat doesn't help dry wetter corn and increases drying speed only slightly. The primary effect of adding heat is reducing the corn's moisture content unless you use a stirring device.
If high-temperature drying, use the maximum drying temperature that won't damage the corn. That increases the dryer's capacity (bushels dried per hour) and reduces energy use. Removing a pound of water will require about 20% less energy at a drying air temperature of 200° F than at 150° F. Follow the dryer company's recommendation, but generally, drying temperatures should be 210-230° F.
"Be aware that excessively high drying temperatures may result in a lower final test weight and increased breakage susceptibility," Hellevang warns. "In addition, as the drying time increases with high-moisture corn, the corn becomes more susceptible to browning."
To prevent corn from scorching or browning during drying, limit dryer temperatures. Exposure to drying air temperatures above 200° F for more than two hours likely will result in some browning. For corn with moisture contents of more than 30%, browning is likely.
The drying temperature and length of time the corn is exposed to the heat affect the potential for discoloration. Producers report that softer, higher-starch kernels may have a higher potential for darkening. Try reducing the temperature to various levels to see which one works best, Hellevang says. Temperature reductions likely will need to vary for corn from field to field.
A cross-flow dryer that moves corn from the inside to the outside of the drying column, varies the corn flow rate across the drying column or varies the corn's exposure to the drying air should be less prone to cause kernel discoloration. Decreasing the temperature in the lower portion of a multistage dryer also will reduce the potential for heat damage.
Another way to reduce the heat damage potential is to dry corn to 20% moisture content instead of 15%. Evaporative cooling still occurs at the higher moisture content, and the kernels will not be exposed to the heat as long when corn is dried to the higher moisture content. This also reduces stress cracks and kernel breakage.
Using combination drying is another option, Hellevang says. For example, dry corn at 28% moisture content to 20% using a high-temperature dryer and store it for the winter, then dry it to storage moisture in the spring using natural air drying or a high-temperature dryer.
Darkening during drying also can be a result of sugar in the kernels becoming caramelized. This is a sign that the corn's development wasn't completed. Corn can be discolored without being graded as dryer-heat damaged. Kernels damaged by dryer heat are almost entirely black.
Using in-storage instead of in-dryer cooling boosts the capacity of high-temperature dryers 20-40%, reduces the risk of stress cracks and removes about 1 percentage point of moisture. In-storage cooling requires a positive-pressure airflow rate of about 0.20 cfm/bu. to cool the corn in about 75 hours. Start cooling immediately after transferring the corn from the dryer to the storage bin to reduce the condensation potential. To further reduce condensation, cool the corn to about 90° in the dryer before placing it in storage.
Dryeration will increase the dryer's capacity 50-70%, reduce energy use about 25% and remove 2-2.5 percentage points of moisture, or about 0.25% for each 10° the corn is cooled. Dryeration is moving hot corn from the dryer to a dryeration bin with a perforated floor, where it remains hot for four to six hours, then is cooled and moved to a storage bin. A tremendous amount of condensation occurs during the steeping and cooling process, so move the corn from the dryeration bin to another bin for storage to prevent spoilage.
Removing debris that accumulates during drying is more critical when outside air temperatures are cold because condensation can develop on the dryer, creating a wet surface where debris can collect. The debris may reduce airflow through the dryer, decreasing the dryer's capacity and creating a fire hazard.
For more information about corn drying, visit NDSU's grain drying website.