Producer Q&A on Grain Storage Affected by Sudden Temperature Drop

Producer Q&A on Grain Storage Affected by Sudden Temperature Drop

Ken Hellevang, grain drying and storage expert and extension engineer at North Dakota State University, answers questions from Nebraska and elsewhere in the Midwest in the following guest article.

Drying operationsFigure 1. Steam was rolling off this grain dryer last week after temperatures plummeted. As of Sunday 91% of the state's corn had been harvested. (Photo by Paul Jasa)
Nov. 21, 2014

Q: With the sudden change in air temperature, what is the best management strategy for running aeration fans on bins to cool grain without freezing the bin?

Corn kernels will not freeze together if the moisture content is below 24%. There is extensive experience with cooling corn to well below freezing and the corn still being able to flow normally. The acceptable moisture content decreases with more foreign material in the corn. I recommend that corn moisture be less than 24% to hold it until outdoor temperatures are above freezing and at or below 21% to hold corn until spring.

Some people are recommending that wet corn not be cooled below freezing because ice crystals will form in the void spaces between the corn with the moisture coming from the corn. Based on extensive experience, I am not aware of this being a problem.

Frosting will occur when moist air comes in contact with a surface at a temperature below freezing. It typically occurs when air from warm corn comes in contact with a cold bin roof and roof vent during aeration. It can occur with corn at temperatures below freezing when warmer air comes through the cold corn. This could occur if the corn at the top of the bin was cold and warm air from corn below is moved through the cold corn as the bin is cooled using aeration. Normally this will occur only in a shallow layer of corn at the top of the bin and only for a period of time until that corn has been warmed by the aeration air coming from the warm corn. The amount of frost accumulation expected in the corn increases as the corn gets colder and the layer of corn gets thicker. Since corn is a good insulator, the cold layer is normally expected to be fairly thin and the warm aeration air removes the frost.

If the corn is warmer than the bin steel, condensation in the form of frost will occur on the bin roof and bin vents. A rapid drop in outdoor temperature makes this very likely. Cooling the corn in small steps reduces this potential. The general goal is to cool the corn to just below freezing. Do this by operating the fans only when outdoor air temperature is above 20°F. Corn at 22% moisture has an estimated allowable storage life of about 60 days at 40°F and 30 days at 50°F. Further cooling of cool corn at the recommended moisture content can be delayed until appropriate temperatures exist. Ideally the aeration air temperature would be 10 to 15 degrees cooler than the corn. If it is extremely cold, it is best to not run the fan and wait for an appropriate air temperature.

Q: Should I place cold grain on warm grain?

Doing this will increase the potential for condensation and frosting in the cold grain. The grain in the bin should be cooled before cold grain is placed on top to avoid frosting. (See the previous answer on what factors lead to frosting within the corn.)  The amount of frost that develops could be enough to restrict or block airflow. The frozen mass would increase the force required to break the ice, so normal stirring devices likely would not be adequate. If an ice block develops, you may need to use an ice auger or other method of breaking the corn apart to permit airflow and unloading.

Q: Does grain harvested at air temperatures below freezing create special concerns?

Corn harvested at temperatures below freezing can be stored, but it should not be placed on top of warmer corn. The maximum recommended moisture content is about 23% to reduce the potential for kernels freezing together. If corn at 25% moisture is placed into a bin with kernel temperatures below freezing, it should flow out of the bin as long as the kernels do not warm above freezing. At 25% moisture there may be enough surface moisture to cause the kernels to stick (freeze) together if they are cooled below freezing.

Q: How should I manage the following three scenarios:
  1. Grain was harvested at 15% moisture with air temperatures at 60° to 70°F. The bin was filled the day before cold air moved in. When would be the best time to run the fan and how long can I wait to start cooling the bin?

    The allowable storage time of 15% corn at 70°F is about 125 days, so there is time to select the appropriate temperature to aerate the grain. As described earlier, there will be extensive frosting on the bin roof if the aeration fan is operated when outside temperature is below freezing and there will be extensive condensation if there is a large temperature difference between the corn and outside temperature with the outside temperature above freezing. As much as possible, select a time to aerate the corn when outside temperature is 40°F to 50°F to cool the corn. This may be accomplished by waiting for warmer weather and running the fan during the daytime. If warmer weather is not expected, run the fan when the outside air temperature is near or just above freezing. Leave the fill and access doors open to minimize the potential for bin vents freezing over and the fan pressure damaging the bin roof. Be aware that frost or condensation will likely occur and may be extensive. Monitor the bin and corn closely and manage moisture accumulation.
     
  2. I have two grain bins, 10,000 bu and 15,000 bu, both filled 1/2 to 2/3 full with corn harvested when temperatures were warm. I ran fans continuously while harvesting, but turned fans off when temperatures dropped below freezing. I have finished filling both bins with corn harvested during the cold snap and have two temperature zones in the bin. What is the best time for running fans to balance temperatures without creating condensation problems? Corn moisture is 16.5% or less.

    The corn in the bottom is warm and at the top is cold. This has been described earlier as a situation that can cause condensation and frosting within the cold corn. The condensation will continue until the warm grain on the bottom has been cooled. In the laboratory the amount of condensation and frost build-up was minimal when warm (70°F) humid air was used to aerate grain at a temperature of 10°F. No visible frost was observed and the wheat moisture content increased by only about 0.5%. This experiment is being repeated with corn. I have heard of frost accumulating in the corn near the top of the bin when running the fan when it is moving very cold air through the corn.  Condensation and/or frosting are expected in the corn if warm corn is cooled with air colder than 32°F. It is not clear if this will cause problems. It is preferable to cool corn in steps, using air at above-freezing temperatures for the first cycle, if possible, and to monitor the condition of the corn.
     
  3. I began filling my last bin with cold corn harvested during this cold spell. Do I need to run the fan much, if at all, since the corn going into the bin was harvested when the air temperature was below freezing?"

    If the corn is cold, it should not need to be aerated. Monitor the corn temperature to assure the grain stays cool in storage, but unless the corn temperature increases, aeration is not required.

Q: I have a question from a farmer who filled his bin half full of corn at 24% moisture about two weeks ago.  This corn is too wet for this bin, which has a natural air dryer. He was running the fans, but shut them down in this cold weather, and now is looking for some advice.  He has had this bin for 35 years, but the wet and very cold temps add a new challenge.

A. Natural air and low temperature drying are not effective at temperatures below freezing, so this type of drying cannot be used until outside air temperatures average about 40 °F, such as with a daily high of about 50°F and low of about 30°F. The maximum recommended corn moisture content for natural air drying is 21% if the airflow rate is 1.0 cubic foot per minute per bushel. Increasing the airflow rate to 1.25 cfm/bu permits drying 22% moisture corn when air temperatures average between 40°F and 50°F. An airflow rate of 2.0 cfm/bu is required to dry 24% moisture corn which is typically achieved by filling the bin only one-half full. The allowable storage time for 24% moisture corn is only 40 days at 40°F and 15 days at 50°F. I discourage trying to dry corn using natural air and low temperature drying at moisture contents over 21%. Corn at 24% moisture generally should be removed and dried in a high temperature dryer before temperatures average above freezing.

Q: A grower still has 50 acres to combine and wants some advice on the options he's considering:

  1. Empty the bin and dry the corn, before adding more corn.
  2. Cool and "freeze" this corn.
  3. Combine the rest of corn, dry, and add to the bin
  4. Don't add this corn to the bin because corn below it not in the right condition for storage.

A: He can hold 24% moisture corn as long as he keeps the temperature near or below freezing. A concern is that 24% moisture corn is at the threshold of the kernels freezing together. It would be safest to remove the 24% moisture corn and dry it. If the remaining corn to be harvested is above 23% moisture it should be dried before placing it into a bin. If it is below 23% moisture, it can be stored if temperatuares remain near freezing, but will need to be dried in a high temperature dryer before late winter. I would not recommend placing additional corn on top of 24% moisture corn due to the unloading and storability concerns.

Resources

For more grain storage information see

Ken Hellevang
Extension Engineer, North Dakota State University