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Schmidt: Addressing grain storage and drying problems

By Staff | Nov 21, 2014

The recent drastic drop in temperature that has occurred may create some special grain storage and drying problems – especially for those still working to harvest corn or sunflowers. Following are some questions that have been received by Ken Hellevang, NDSU Extension Agricultural Engineer, and his responses. The questions are italicized and Ken’s answers follow the questions.

“With the sudden change in air temps, what is the best management strategy for running aeration fans on bins to cool grain without freezing the bin?” – The kernels will not freeze together if the corn moisture content is less than 24 percent. 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 percent to hold it until outdoor temperatures are above freezing and at or less than 21 percent to hold corn until spring.

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

Frosting will occur when moist air comes in contact with a surface at a temperature less than 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 warm aeration air coming from the warm corn. The amount of frost accumulation expected in the corn increases as the corn gets colder and 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. The 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 less than freezing, so operate the fans only when outdoor air temperature is more than 20 degrees. Corn at 22 percent moisture has an estimated allowable storage life of about 60 days at 40 degrees and 30 days at 50 degrees. Cool corn at recommended moisture contents can wait for cooling 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.

“Should I place cold grain on top of warm grain?” – 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. Review the explanation of the conditions that may lead to frosting within the corn. Placing cold grain on top of warm grain creates the conditions expected to cause frosting problems. The amount of frost may be enough to restrict or block airflow. The frozen mass would greatly increase the force required to break the ice, so normal stirring devices likely would not be adequate. It may require using an ice auger or other method of breaking the corn apart to permit airflow and unloading.

“Does grain harvested at air temps below freezing create special concerns?” – Corn harvested at temperatures less than freezing can be placed into storage, but should not be placed on top of warmer corn. The maximum recommended moisture content is about 23 percent to reduce the potential for kernels freezing together. If corn at 25 percent 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 percent moisture there may be enough surface moisture to cause the kernels to stick (freeze) together if they are cooled below freezing.

For more information on grain storage visit ag.ndsu.edu/graindrying.

Winter Grain

Storage Basics

Grain should be cooled to about 25 degrees for winter storage to limit moisture variation and control insect problems. Insects in stored grain can be killed if this temperature is maintained during winter storage.

Grain in storage needs to be checked to be properly managed. Check for indications of moisture such as grain crusting or condensation on the bin’s roof, and smell for musty, moldy odors. But just this is not adequate. It is essential to use a probe to collect samples from various locations.

Check and record the grain temperature at several locations in the bin. Both the temperature and trend in temperatures are important; both mold growth and insect activity will cause the temperature to increase.

Check the grain moisture content. The reading must always be adjusted based on the grain temperature, but remember that the moisture content reading is inaccurate at temperatures below 40 degrees. It is best to check the moisture content of collected samples after the grain has been warmed to room temperature. Warm the grain in an air-tight container, such as a plastic bag, to prevent the moisture content from changing during warming.

Also check the samples for insects after they have warmed to room temperature. Placing the grain on a white background will make it easier to see the insects. Cooling the grain to about 25 degrees is the best way to control the problem if insects are found.

Make sure all openings in the bins, such as vents and ducts, prevent snow from getting into the bin. These openings need to be there to allow air flow during aeration, but may be closed once aeration has been completed. Fans should be covered when they are not operating.

High-moisture grain can be stored over the winter as long as the grain is kept cold. Corn at 24 percent moisture can be stored for about 130 days if the grain temperature is below 30 degrees, but the allowable storage time decreases drastically at warmer grain temperatures. The estimated allowable storage time for 24 percent moisture corn is 40 days at 40 degrees, but only 15 days at 50 degrees.

Corn with less than 21 percent moisture can be natural-air dried in the spring using an airflow rate of at least 1 cubic foot of air per minute per bushel by starting the fans when the average temperature is about 40 degrees. Corn at moisture content exceeding 21 percent should be removed for high-temperature drying before temperatures rapidly warm during March. Solar heat gain will warm the top of the bin and the south wall to temperatures exceeding outdoor air temperatures.

Grain will deteriorate even with the fan operating. Airflow keeps the grain cooled to near the air temperature, but the grain still will deteriorate at a rate based on the grain moisture content and temperature.

Grain is more susceptible to deterioration if it is immature or the kernel integrity is damaged. Poor quality grain should be dried to a moisture content about 1 percentage point lower than good quality grain. Poor quality grain should be monitored more closely during the storage period.

There will be a grain moisture content variation among kernels after drying in a high- temperature dryer if there was a moisture content variation before drying. For example, if the kernels vary in moisture between 20 percent and 30 percent before drying, the variation may be between 12 percent and 18 percent after drying. Due to the variations in maturity within fields and even on a single corncob, there is potential for variations in stored grain moisture content. Grain segregates based on size and density as it flows into a bin. If there is a variation in kernel size, pockets and variations should be expected. Some of these pockets may contain grain at higher moisture content. If a grain spreader has not been used to fill a bin, normally the smaller and denser material accumulates in the center of the bin.

Grain germination may be damaged before visible mold is present on the kernels. This may happen when wet grain remains in a bin at moderate temperatures for an extended period before it is dried. Germination should be checked on malting barley and seed that was not dried within three weeks of being placed in the bin.

There is the potential for bin vent screens to become iced over when operating fans near or below freezing temperatures causing damage to bin roofs. If fans must be operated near or below freezing temperatures, it is recommended to leave a bin fill-hole or manhole unlatched as a pressure relief valve if the air is being pushed up through the grain. If humid air is being pulled in through bin vents at temperatures near freezing, provide an unscreened opening, such as the manhole, for airflow.

Check the grain every couple of weeks until it has been cooled to 20 to 25 degrees. Check dry grain at least monthly during the winter and wet grain every couple of weeks. Measure and record the grain temperature. Check the grain moisture content and examine the grain in several locations. Search for small changes that are indicators of potential problems.

High moisture grain is more likely to develop a crust, which may hide a cavity formed when the grain is unloaded. The chance of suffocating is high if you fall into the cavity and are covered by the grain. Grain stuck to the wall of a bin can also trap and suffocate a person attempting to break it loose. It is not healthy to breathe mold spores and suspended mold particles that may be in the air of a bin with deteriorating grain. Always wear at least an N-95 rated mask or respirator if in a bin with spoiled or moldy grain.

For more information on grain storage visit ag.ndsu.edu/graindrying or contact the Pierce County Extension office at 776-6234 ext. 5 or yolanda.schmidt@ndsu.edu.

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