Helping your grain keep its cool

When temperatures begin to fluctuate and rise as we approach the spring and summer months, keeping grain cool and dry is the best defense against insect activity and mold. 

Ken Hellevang, a grain storage expert and Extension agricultural engineer for the North Dakota State University Extension Service, suggests checking stored grain every two weeks at the least. 

While checking on grain, measure and record grain temperature and moisture content. Rising grain temperature may indicate insect or mold problems. Insect infestations can increase from being barely noticeable to major infestations in three to four weeks when the grain is warm.

Checking the temperature

While temperatures may be higher in the midst of summer, more heating occurs on the south wall of a grain bin in the spring. This heats the grain next to the bin wall to temperatures higher than average outside temperatures. This is of more concern if the grain exceeds recommended storage moisture contents.

“Not only will daytime temperatures be increasing, but the bin works as a solar collector,” Hellevang says.

Hellevang recommends running aeration fans periodically during spring to keep grain temperatures cool. Ideal temperatures are near 30°F. in the northern part of the country during March and April and below 40°F. in southern regions. Nighttime temperatures typically are near or below 30°F. in March and below 40°F. in April across the north-central region of the United States.

He also recommends not relying too heavily on temperature sensors and to place a temperature cable a few feet from the south wall of a bin.

“Temperature sensors are an excellent tool, but remember that they only measure the temperature of the grain next to the sensor,” Hellevang says. “Because grain is an excellent insulator, the grain temperature may be much different just a few feet from the sensor and not affect the measured temperature.”

Aeration optimization

Keep aeration fans or ducts covered when they aren’t operating. The wind and a natural chimney effect will push warm, moist spring air through the grain. If the wind blows primarily during the daytime, the grain will be warmed to the daily maximum temperature. 

Typical maximum temperatures, even in northern states in late March, are in the mid-40s (°F.) and increase in late April to around 60°F. Also, grain moisture will increase as the grain is warmed.

To reduce hot air in the top of the bin, provide an air inlet near the bin roof eave and an outlet near the peak. Similar to venting an attic in a house, the heated air rises and is exhausted at the peak.

A ventilation fan to exhaust the hot air is another option. Hot air under the bin roof will heat several feet of grain at the top of the bin to temperatures conducive for insect infestations. Running the aeration fan for a few hours to push air up through cool stored grain will cool other grain near the top.

Pick a cool morning every two to three weeks during the summer to run the aeration fan, and only run the fan a few hours to minimize heating grain at the bottom of the bin. Cover the fan when it is not operating to prevent additional heating of the grain.

Avoiding moisture and mold

Having grain at an appropriate warm-season storage moisture content is important for storing grain safely during warmer months, according to Hellevang.  

Maximum moisture content for warm-season storage: 

• Corn: 13% to 14%
• Soybeans: 11% 
• Wheat: 13.5% 
• Barley: 12% 
• Oil sunflowers: 8%  

Mold growth occurs at higher temperatures if the grain exceeds the recommended moisture content. The allowable storage time for corn at 15% moisture is only about four months at 70°F. and two months at 80°F.

Checking grain moisture content is important because moisture measurements taken at harvest may have errors due to moisture gradients in the kernel, grain temperature, and other external factors. In addition, moisture content may change while grain is in storage due to moisture migration or moisture entering the bin.

When checking moisture content, follow the moisture meter manufacturer’s procedure for obtaining an accurate moisture measurement. Temperature adjustments, cold grain, inaccurate sample quantity, and moisture variations across the kernel frequently cause substantial measurement errors.

You can verify the accuracy of the measurement by warming the grain sample to room temperature in a sealed plastic bag before measuring the moisture content. After a period of six to 12 hours in a sealed container, grain moisture reaches equilibrium across the kernels. Compare the on-farm measured value to that of the sample using a meter at the elevator or other market location.