Bill Wilcke, Minnesota Extension Engineer
This spring, a lot of farmers and other stored grain managers are concerned about the effect of our abnormally warm winter temperatures on their stored grain. And they’re wondering how they should be managing aeration fans on their dry-grain storage bins. Appropriate aeration and fan management depends on the current temperature and condition of the grain. There are two basic objectives for aeration of dry stored grain:
1) Keep the grain cool enough that molds and insects are not active. Molds and insects grow and reproduce rapidly at temperatures greater than 60°F, so it’s best to keep the temperature of stored grain less than 60°F at all times. This means that whether fans are operated manually or by using automatic controls, fan operation should be avoided when outdoor temperatures exceed 60°F. Molds and insects are less active at lower temperatures, so it is better to keep stored grain well under 60°F. In fact, in the upper Midwest, we suggest winter storage temperatures of 20° to 30°F and summer storage temperatures of no more than about 50°F.
2) Keep the grain temperature close enough to the average outdoor temperature so that there aren’t problems with moisture migration and condensation. If stored grain is too much warmer than outdoor temperatures during winter, moisture will tend to move from the warm areas of the grain pile to the cold areas and moisture will condense on the cold grain. Over time, the re-wetted grain will develop mold and insect problems and start to heat and form a crust. Wintertime stored grain temperatures of 20° to 30°F in the upper Midwest are close enough to average outdoor temperatures that moisture migration can usually be avoided. In summer, if the grain temperature is too much colder than the outdoor air temperature, any warm, humid air that comes into contact with the cold grain will cause moisture to condense on the grain. Holding grain at 30° to 50°F during summer in the upper Midwest is usually close enough to the average outdoor temperatures that we can avoid major condensation problems.
Before deciding whether to run aeration fans, managers should first measure the temperature at several points in the grain bin or pile and check the condition of the stored grain (look for molds, insects, and bad odors). If the grain temperature is between 30° and 50°F and no quality problems are detected, no aeration is required. They should just keep checking the grain every week or two and run the fans only if problems are detected later on. If the grain is warmer than 50°F, they should watch for weather in the 30° to 50°F range and operate fans to cool the grain. If the grain temperature is much less than 30°F, they should watch for weather in the 30° to 50°F range and operate fans to warm the grain. Managers who decide to warm their grain need to be aware that some condensation occurs during the grain warming process and that once they start the fans, they need to keep them running until the warming front has moved all the way through the bin.
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