After you've dried your corn to a safe storage moisture (15% for winter storage, 14% for storage through summer, 13% for a year or more of storage), you're not quite finished, yet. You still need to cool the corn to a temperature that is low enough to limit mold and insect activity.
For corn that is dried in heated-air dryers, the first step is to remove dryer heat. There are three options for cooling hot, freshly-dried corn:
1. Cool corn rapidly in the dryer. This is fast and fairly effective, but it really stresses the kernels and leads to a lot of kernel cracking. It also results in a lower test weight than for slower cooling. Almost no moisture is lost during rapid cooling and corn usually remains about 10°F warmer than the outdoor temperature.
2. In-storage cooling. Hot corn from the dryer is placed directly into a storage bin and is cooled slowly by the bin's aeration fan. This method requires a good aeration system with a fan that is sized to keep up with the dryer. (Provide at least 12 cubic feet of air per minute (cfm) per bushel per hour of dryer capacity.) But compared to rapid cooling in the dryer, in-storage cooling results in slightly better corn quality, one to two points more moisture loss, and greater dryer capacity. Some condensation occurs along bin walls, especially during cold weather, so run aeration fans extra time to remove the condensed moisture, or consider moving the corn soon after cooling is complete.
Full perforated floors are best for in-storage cooling, but the process can work in bins that have duct systems or square pads in the center. However, without a full-perforated floor, cooling rates vary in different parts of the bin and you need to take more temperature measurements to make sure all corn has cooled before you turn off the fan.
3. Dryeration. Hot corn from the dryer is placed in a cooling bin, kept hot for 4 to 12 hours, cooled in 12 to 24 hours, and then moved to storage. Dryeration results in excellent grain quality and provides a two- to three-point moisture loss during cooling. Because so much condensation occurs inside the walls of the cooling bin, it is best to move corn after cooling to prevent spoilage next to the walls.
After dryer heat has been removed from corn, wait until the average outdoor temperature (divide the sum of the daily high and daily low by two) is 15 to 20°F less than the corn temperature. Then, start the aeration fan and let it run until a cooling front moves all the way through the bin. During cooling, stored grain does not all cool at once. Instead, cooling takes place in a zone, or front, that is several feet thick and moves through the grain in the same direction as the cooling air.
The target grain temperature for winter storage in the upper Midwest is 20 to 30°F. It often takes several cooling cycles to get grain cooled to this level. For example, it is not unusual to have a corn temperature of 60°F after dryer heat is removed. Cool the grain again in mid-fall when average outdoor temperatures reach 40 to 45°F. Then, initiate the final cooling cycle in early winter when outdoor temperatures reach 20 to 30°F.
The time it takes to move a cooling front through a bin depends mainly on the airflow per bushel provided by the aeration fan. As a rough rule, cooling time in hours is equal to 15 divided by cfm per bushel. Storage bins are often designed for an airflow of 0.1 cfm/bu, so cooling times of 150 hours are common. The Minnesota Extension Service has a computer program available to help you estimate the airflow in storage bins.
Be aware that the calculation for cooling time provides only a rough estimate. You still need to measure grain temperatures at several points in the bin to verify that all grain in the bin has been adequately cooled. Once grain has been cooled to winter storage temperature, you can turn the fan off and leave it off unless abnormal outdoor temperatures or mold problems cause the grain temperature to change.
This page is part of the Biosystems and Agricultural Engineering Department web at http://www.bae.umn.edu/