A lot of grain in the upper Midwest was stored at abnormally high temperatures this year. Unless this grain is aerated with cool outdoor air, the temperature in the center of the grain bin or pile will remain high well into winter. A warm center in grain storage leads to two problems. First, insects and molds are more likely to infest the warm areas. And second, temperature differences in stored grain cause moisture to migrate from warm areas to cold areas, with resultant mold growth and crust development in the rewet areas.
Target grain temperatures for winter storage in the upper Midwest are in the 20° to 30°F range. If current grain temperatures are 40° to 50°F, wait for outdoor weather that is 20° to 30°F, start the aeration fans, and run them as long as necessary to cool all grain in the bin or pile. The amount of time that fans need to be operated to complete cooling depends on the airflow per bushel. Typical grain aeration systems deliver about 0.1 cfm/bu (cubic foot of air per minute per bushel of grain); at that airflow, you can expect cooling to take about 150 hours. Some of the temporary grain storage facilities that are being used this year have aeration systems that deliver less than 0.1 cfm/bu, which means aeration cycles could take much longer than 150 hours. Many temporary storage facilities have non-uniform airflow, where some parts of the grain pile have a much lower airflow per bushel than other parts. In situations where airflow is not uniform, it is important to check grain temperatures at many different points and to run the fans until all parts of the pile are cooled.
If current grain temperatures are much higher than 50°F, it is probably best to cool the grain in 15 to 20 degree stages. For example, if the grain is currently 65°F, wait for 40° to 50°F weather, and run the fans until the grain is cooled to that range. Then, stop the fans until outdoor temperatures drop another 15 to 20 degrees, and resume fan operation until all grain is cooled to 20° to 30°F.
Either positive pressure (air pushed upward) or negative pressure (air drawn downward) can be used to aerate grain. However, positive pressure aeration systems do tend to provide more uniform air distribution in large grain piles that have long aeration ducts. One thing to watch for, though, with positive pressure systems is condensation under the roof when you aerate warm grain during cool weather. You can reduce condensation problems by opening doors and hatches to provide plenty of air movement over the top surface of the grain during aeration and by cooling grain in stages so that the difference between outdoor temperature and grain temperature is less than 20 degrees.
Once grain is cooled to 20° to 30°F, you might not have to aerate it again during the winter. Check the grain every two to four weeks for signs of mold, insects, crusting, or heating and if you find problems, start the fans to try to cool and dry the problem area. If aeration doesn't seem to be working, remove the problem grain to prevent additional spoilage.
This page is part of the Biosystems and Agricultural Engineering Department web at http://www.bae.umn.edu/