industrial fan attached to a grain bin
COOL IT TO KEEP IT: You should maintain stored grain between 30 and 40 degrees F or below to reduce mold and insect activity.

It’s time for farmers to turn on the bin fans

Stored corn and soybeans need to be cooled down for safekeeping.

Until late October in Iowa, the 2017 harvest season has been short on favorable weather for grain to dry down in the field. This fall was also short on weather for cooling harvested grain stored in bins. Corn moisture percentages were hanging in the 20s, sometimes in the upper 20s, on grain coming out of the field.

When the weather finally turned drier and colder the last week of October, it eliminated much of the grain moisture from the ears on stalks standing in the field awaiting harvest. However, favorable drydown weather rarely continues in November. 

In November, Charlie Hurburgh, director of the Iowa Grain Quality Initiative at Iowa State University, is advising farmers they should now focus their attention on cooling the harvested grain, both the wet corn being held in bins and corn that’s being dried with natural, unheated air. Likewise, dried corn that’s being removed from dryers needs to be cooled as it is put into storage. 

Cool down corn right away
“Inadequate or delayed cooling is very costly to future storage properties of the grain,” says Hurburgh. “Remember, a significant portion of this 2017 crop will be held in storage for more than one year, as carryovers expand.”

Starting Oct. 27, great conditions arose in Iowa to get grain from this fall’s harvest cooled down. “When the average daily temperatures are in the mid-30s to low 40s, that’s a perfect time to get recently harvested corn and soybeans cooled down to a temperature required for winter storage,” says Hurburgh. “Allowable storage time for grain roughly doubles for every 10 degree drop in temperature. So, getting grain cooled down soon after harvest will significantly improve the chances of keeping it in good condition while in storage.”

To determine the length of time it will take to cool a bin of grain, Hurburgh says you need to first determine how much fan horsepower you have per 1,000 bushels. For example, if you have a 5-hp fan on a 20,000-bushel bin, you have 0.25 hp per 1,000 bushels. Divide this number into 15, and you get an estimate of the hours it will take to cool the full bin. In this example, 15 divided by 0.25 equals 60 hours.

Grain doesn’t cool when dew point too high
Air dew point is a rough measure of how low the grain temperature can be reduced, says Hurburgh. For example, if the outside air temperature is 63 degrees and the dew point is 44 degrees, that’s approximately a 20-degree difference. A 20-degree difference is good. The larger the difference, the greater chance that the air will dry the corn, and 44 degrees is approaching the below-40-degree temperatures required for storage.

There will be a lot of long-term storage of corn and soybeans this year, so cooling your grain rapidly now is a wise step to take, to prevent mold and insect damage next spring and summer.

Hurburgh says it takes about 150 hours for a fan moving air at 0.1 cubic feet per minute per bushel to make a full change in grain temperature (a cooling cycle). The time it takes to complete a cooling cycle for a bin of stored grain is proportionately different for higher and lower airflow rates, which means bins designed with airflows above those necessary for aeration alone can take advantage of shorter periods of favorable cooling conditions.

Check stored grain regularly during winter
Monitor your stored corn and soybeans closely each week or at least every two weeks this winter, advises Hurburgh. Turn the fan on and record the temperature of the air coming out of the grain to see if the grain is heating up while in storage. A rise in temperature over a short time is an indicator of pending problems in that grain.

Also, when you run the fan, smell the first air that comes out, he adds. Beware of any smell or crusting of grain or an increase in the moisture content at the surface of stored grain. Take action immediately if warning signs are detected. If possible, check the top surface of the grain, but never enter bins alone.

For more information on managing stored grain, visit

TAGS: Corn Soybean
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