With the weather forecast calling for average day and night temperatures of 35 to 40 degrees F in the coming 10 days, the time is right to cool any grain that went into the bin at higher temperatures.

That’s the message from Iowa State University grain quality expert Charlie Hurburgh. He’s the professor in charge of the Iowa Grain Quality Initiative at ISU. He offers tips and rules of thumb for cooling and storing grain through the winter.

“You may be in the thick of harvest, but don’t forget to cool stored grain,” he says.

Recent reports have Iowa corn about 40% harvested and soybeans about 66% harvested. The late crop has corn moisture content running from around 19% in central and western Iowa to 25% and above in northern and northeast Iowa. 

Will corn dry down in field?

With the late-planted corn especially, this year’s crop has been slow to mature and slow to dry down naturally in the field this fall. “Leaving corn standing in the field to dry down is very slow after the end of November,” Hurburgh says. “Because of immaturity, corn is drying slower than normal in the field this fall, and it’s requiring more fuel per unit of moisture if you are drying with heated air dryers.”

Cold grain temperatures are the best protection against spoilage at this point, he says. The allowable storage time (shelf life) of corn nearly doubles with a reduction in grain temperature from 50 to 40 degrees. This can allow drying to stop at a higher moisture, and the grain can still be stored through the winter, he explains. 

For example, 17% moisture corn has a storage life of 5.3 months at 50 degrees, but 9.4 months at 40 degrees. Soybean storage properties are about like corn — that is, 2% drier. In other words, 15% soybeans store similar to 17% corn. For a table of storage time and temperature, visit ISU Extension. 

Watch dewpoint

“The weather forecast as of Oct. 30 is for several days of cold weather — highs in the 40s, lows in the 20s,” Hurburgh says. “This will be a very good time to get stored grain cold enough to substantially reduce mold activity. 

The key temperature to watch is the dewpoint — the condensation temperature. That’s because air moving through wetter material such as wet grain will cool by evaporation to nearly the dewpoint. For example, the temperature outside in Ames on Oct. 29 was 34 degrees, but the dewpoint was 21 degrees. These are excellent cooling conditions for running air on stored grain.”

Looking at the weather forecast, this coming week to 10 days will be a good period to run fans on stored grain — corn and soybeans. “If we can’t get the corn dried down quickly,” he says, “cold temperatures have to be the protection against spoilage, to keep spoilage from developing.”