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COOL IT: Maintaining a uniformly cold grain temperature by using aeration is the key to holding wet corn until it can be dried or sold.

Dealing with wet corn

With wet grain and spot shortages of LP gas for drying, proper aeration is needed.

With a late-maturing, wet corn crop this fall, demand for propane to run grain dryers is stronger than usual and causing spot shortages of the fuel. Elevator reports in mid-November estimate wet corn from fields at 20% moisture in central and western Iowa, and up to 25% moisture or higher in northern and eastern Iowa.

What do you do with wet corn while waiting for the propane dealer to come?

“Use the cold weather wisely when aerating the corn and you’ll be OK,” says Charlie Hurburgh, director of the Iowa Grain Quality Initiative at Iowa State University. “Cold weather allows us to hold the wetter grain in the bin for a while until we can get back to drying it. That’s very important. Don’t let it sit in trucks, wagons or hopper tanks that don’t have any aeration. Wet grain needs aeration while waiting to be dried. Corn that’s harvested wet should be put immediately in a bin that has a fan for aeration.”

Dry it down later for safe storage

To safely store corn through winter, dry good-quality corn to 15% moisture, Hurburgh says. To store into the summer, dry it to 13%. Dry low test-weight corn and corn with damaged kernels to a 1% lower moisture content than normal.

If corn harvested this fall is in an aerated bin at 17% or 18% moisture, but it still needs to be dried down for safe storage, dry it as soon as possible. “The 2019 corn crop is not going to keep well,” he says. “Test weight is generally lighter than normal, and protein is lower, too. The temptation for farmers is to say, ‘OK, we got the crop harvested and in the bin, and with aeration we’ve got the grain temperature down to 30 degrees to 40 degrees F, so we can just hold it there through winter without drying it.’ But no, don’t do that. You’ll be experiencing 2009 all over again.”

The 2009 crop was below average in quality due to late planting, subsequent immaturity and incomplete grain fill. Immature corn has a lower test weight and protein, and poorer mold resistance. Replanted and late-planted corn varies greatly in moisture that can’t be fully evened out in high-temperature dryers; pockets of wet grain will be in the dry corn. Bin dryers with stirring machines are better at evening out moisture but have much lower throughput capacity than high-temperature batch or continuous-flow driers.

Immaturity has also made 2019 corn harder to dry, Hurburgh says. Elevators are reporting 5% to 10% increases in energy use per unit of moisture removed. A soft texture makes corn hang on to the water tightly. This means the allowable storage time is shorter than normal (see table).


Maintaining a uniformly cold grain temperature is the key to holding wet corn until it can be dried or sold. Grain will cool by evaporation to nearly the dewpoint (when water will condense). The dewpoint is lower than the actual air temperature, unless the air is 100% relative humidity. Airflow rates typical for aeration of dry corn (0.1 cfm per bushel or higher) will be enough for cooling but not drying.

Corn can be stored at temperatures below freezing. The risk is having frozen chunks that obstruct airflow or jam conveyors. Frozen corn should be as clean as possible, Hurburgh says. Remove some grain from the center of the bin. This will take out fines, move the grain, level the surface for air distribution, and provide a sample for temperature measurement if the bin doesn’t have temperature cables or is too deep for surface probing alone. Removing one load of this cored grain should be enough in medium-size farm bins, less in small bins and more in larger bins.

Dewpoint key indicator

Pay attention to weather forecasts. Don’t rewarm wet corn during a warm spell, Hurburgh says. Consider 35 degrees as the upper limit for grain temperatures for wet corn. The dewpoint is critical to follow. On low-humidity days, low dewpoints can occur even with moderate air temperatures; 50-degree air with 40% relative humidity will have a dewpoint of 30 degrees. 

“If the weather forecast calls for a few days of warm weather, dewpoints will be above freezing,” he notes. “It would be counterproductive to keep the fans running during this period.”

Weekly records of exiting air temperatures at each fan, or at the top with upflow aeration, will give indications of temperature stability in the grain mass but will not necessarily identify pockets of heating. “Dry the corn or sell it as soon as you can, even if this means some extra handling,” Hurburgh says. “The longer that wet corn stays in a bin, even cold, the higher the risk of spoilage in some places, such as along a wall that gets warmed on sunny days. Storage life loss shows up in the spring with hot spots, blue-eye mold and eventually serious spoilage.”

If drying is slowed but still possible, consider drying to an intermediate moisture (17% to 18%). Then put the corn in an aerated bin, cool it and finish drying later. You gain storage time by reducing the moisture.

“In 2009, we had significant amounts of corn left in the field over winter due to high moisture and insufficient drying capacity,” Hurburgh says. “The corn reached about 18% moisture, the long-term equilibrium for winter air in Iowa. There were some mold issues, but not from fungi that produce mycotoxins. Stalk lodging and snow cause field loss to the ground, which is a risk when leaving corn in the field. The abnormally early cold temperatures this fall are providing a significant benefit this year, in the holding of higher-than-normal moisture corn until it can be dried or used.”

For more information, visit ISU's Iowa Grain Quality Initiative.

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