KANSAS CITY, MISSOURI, US — As winter clutches the Northern Hemisphere in its chilly grasp, it is essential that stored grain is tucked in tight for the next several months. 

During cold weather, maintaining the proper moisture and temperature are key to ensure grain stays in condition until spring. Drastic temperature differences between grain and ambient air can lead to moisture problems and snow or icy weather can freeze equipment or lead to power outages. 

If grain goes out of condition, it can lower the value or become a hazard to workers. From a safety perspective, out-of-condition grain can cause health hazards, especially when grain dust contains mold and bacteria, according to Ohio State University (OSU) Extension. It also can form a crust or stick to the bin walls, creating conditions that could lead to grain entrapment should someone enter the bins.

“Cold weather per se has no negative impact on grain quality or safety of handling grain,” said Dirk Maier, professor of agricultural and biosystems engineering at Iowa State University in Ames, Iowa, US, and renowned expert in grain storage and handling. “What’s important is to aeration-cool stored grain to target temperatures, maintain grain at safe storage moisture content and monitor stored grain for CO2.”

Ideal moisture 

Safe storage moisture for the length of the planned storage period is the most important factor for grains such as corn, Maier said. For example, if corn will be shipped or utilized by the end of the cold season, it can be safely stored at 15% to 16% moisture as long as grain temperatures are below 40 degrees Fahrenheit and average ambient temperatures are below 50 degrees Fahrenheit.

Once ambient temperatures increase, especially during the day consistently above 60 degrees Fahrenheit, safe storage moisture content needs to be below 15% and grain temperatures below 50 degrees Fahrenheit. 

“When average ambient temperatures increase above 70 degrees Fahrenheit, safe storage moisture content reduces to 14% with average grain temperatures below 60 degrees Fahrenheit,” Maier said. 

Aeration cooling into the low 30s and soybeans into the low 50s in two to three thermostat-controlled cooling cycles minimizes shrink loss and maintains target market moisture content, he said. Soybeans do not need to be cooled to as low of a temperature as is generally recommended for corn, Maier said. Cooling dry soybeans to 50 degrees Fahrenheit reduces shrink potential and electric energy costs. 

Proper bin sealing prevents moisture, as well as pests, from compromising the grain. Consider upgrades such as insulated bin covers or improved weatherproofing. 

Grain bin sensors can be used to measure moisture content across different layers, and aeration settings can be adjusted or the grain redistributed if moisture levels vary significantly. 

Moisture migration occurs when a 20-degree temperature difference occurs between the grain and the average outdoor temperature, said Ken Hellevang, professor emeritus and retired North Dakota State University Extension agricultural engineer. It increases the moisture content of the grain near or at the top of the bin. This can increase the moisture content by several percentage points and lead to crusting of the grain. 

Temperature check

Most grain spoilage is the result of storing grain at too warm a temperature over the winter, so cooling and keeping grain cool is critical, said OSU Extension. Look for days with no precipitation when the outside air temperature is 10 degrees to 15 degrees Fahrenheit cooler than the temperature of the grain. The goal is not to freeze the grain, just cool it to the point that insect activity and mold growth is slowed or stopped. 

Equalize the temperature by running fans periodically to even out the temperature inside the bin and reduce condensation risks. The time it takes to move a cooling front through the bin depends on the cfm/bu of the fan. For most bins, this is between one to four days but some may take longer. 

Cooling fronts through a peaked corn mass do not move uniformly, Maier said. It can take two to three times longer to cool out the core and peak than the rest of the grain mass. 

The center is the most common area for spoilage because of an increased concentration of fines restricting air movement, OSU Extension said. In the winter, cooling process bins should be cored to remove 99% of the fines. 

Removing the core and unpeaking the grain mass should occur in each bin as soon as some corn can be moved to ship, transfer or process, Maier said. 

To properly core a bin, remove the entire peak creating a funnel shape inside. A proper core funnel starts at the bin wall, not part way up the current peak, OSU Extension said. 

“A cooled, cored, unpeaked grain mass at safe storage moisture content with stable CO2 readings can be held well into the warm weather period of the marketing year,” Maier said.     

Other things to keep in mind include covering aeration fans when they are not in use, said South Dakota State University (SDSU) Extension. The fans have a “chimney effect” where wind moves air into the fan and it travels upward, affecting the grain inside.

“Although this can be favorable during cold and dry periods, fans should be covered during snow events,” it said. 

Provide an inlet for air near the roof eave and outlet exhaust near the roof peak to allow warm air to exit the bin. Several vents at the same elevation can still allow heat to remain at the top of the bin without exhaust at the peak or roof exhaust fans. Without the proper ventilation, condensation can occur. 

Bin vent screens could also become iced over when operating fans at temperatures near or below freezing, Hellevang said. He recommended leaving a bin fill hole or manhole unlatched as a pressure relief valve if the air is being pushed up through the grain. 

Inspect and monitor regularly

Grain should be checked at least every two to three weeks as long as the grain is at winter storage temperature of 20 to 30 degrees Fahrenheit, Hellevang said. Check more frequently if it is warmer.

Measure and record the grain temperature, looking for trends that indicate problems. Check the grain moisture content and examine the grain in several locations. 

Verify the accuracy of the measurement by warming the grain sample to room temperature in a sealed plastic bag before measuring the moisture content. Moisture measurements of grain at temperatures below about 40 degrees Fahrenheit are not accurate, he said. 

Grain temperature near the bin wall and on the top surface depends on the outdoor temperature and solar radiation. For example, the amount of solar energy on the south wall of the bin will be two to three times as much on Feb. 21 as on June 21 due to the low solar angle, Hellevang said. 

In late winter and spring, monitor the grain temperature particularly near the south wall and near the grain surface, he said. Temperature monitoring is possible with cable-monitoring systems that evaluate entire bin temperatures and can catch hot spots caused by spoilage and insect activity. 

Another effective strategy for monitoring stored grain of any type is measuring carbon dioxide in the headspace above the grain mass and optionally in the plenum or ducts below the grain mass. Carbon dioxide is an early detector of biological activity such as grain respiration, which happens at higher moisture contents; mold growth, which is triggered by water or snow infiltration or roof condensation; and insect infestation, typically mold feeders before grain weevils or borers.

“Research has shown that rising CO2 levels can give a stored grain manager an extra three to four weeks for decision making compared to relying on traditional temperature sensing cables,” Maier said. 

Maier also recommended the Aeration & Storage of Grains app developed by ISU, which is available for Android and iPhones free of charge. Its features include determining the safe storage moisture content for many grains for a wide temperature range. 

At ISU, researchers use the new grain center to examine the advantages of screen-cleaning dry corn before going into storage. During the past fall harvest, they identified several benefits, including faster aeration cooling cycles when comparing uncored and peaked corn that was screen-cleaned versus not. 

“We are also able to reduce even the smallest amounts of mycotoxin levels substantially in screen-cleaned corn intended for storage into late summer and early fall,” Maier said. “Having our own feed mill allowed us to utilize screenings from the harvest season in feed rations instead of storing them with corn in our bins.”

Keep in mind that the ice, snow and strong winds that come with winter can disrupt power supplies or damage equipment. Take a proactive approach that includes backup systems or manual methods to manage grain conditions temporarily. Any grain management strategy should include contingency plans for sudden cold snaps or unexpected equipment issues.