Thursday, September 29, 2011
Protect That Valuable Asset Stored In Your Grain Bin
Your yields may be a bit disappointing this year, but harvest is progressing and your grain bins are filling up. Just for the sake of discussion, let’s say you have 800 acres of corn that averages 140 bushels per acre. You are a long way from a river or processor and your corn is worth only $6. You still have $672,000 of corn stored in the bin, and nearly all is needed to pay cash rent and put in next year’s crop. That grain bin becomes your bank, and most banks are protected to ensure nothing happens to the assets in the vault. Is the bank vault at your farmstead protected?
One of the reasons farmers only do a mediocre job of marketing is the pride of ownership of what is in the bin, and they don’t want to let go of it. But if you are so proud of that grain, it needs to be protected from spoilage, and Ag Engineer Ken Hellevang of North Dakota State University, offers his suggestions for protecting that investment.
Grain storage is impacted by either mold growth or insect infestation. Mold growth is a function of moisture and temperature. Each different type of grain has a recommended moisture content that will prevent mold growth, which leads to spoilage. The grain chemistry and physical characteristics determine what moisture allows a humidity level under 60% which is the typical threshold for mold growth. That moisture level allows the grain to be stored successfully, and for corn specifically, storage is recommended in the 13-14% moisture level for long term storage. Hellevang says that requires an equilibrium moisture content of 12.8% in the grain to restrict the humidity of the corn to under 60%.
With the critical nature of grain moisture, he said it must be measured accurately. Most moisture meters are calibrated for dry grain, so if corn is at 25-28% moisture the meter will not give an accurate reading. Meters are calibrated at a certain temperature range, so if the grain temperature is too warm or too cold, the meter will not give an accurate reading, particularly below 40ºF. Most of the electronic meters are more sensitive to the outside of the kernel, and Hellevang said grain coming out of a high speed dryer cannot be accurately tested for moisture because of the differences in temperature from the inside to the outside of the kernel. Condensation on the kernel will also cause errors in electronic meters. Hellevang suggests placing the grain sample in a zip lock bag for several hours at room temperature to get uniform temperature and moisture of the sample before measuring it. By re-checking 12 hours later, it will give an indication of how to adjust the meter to provide a better indication of moisture.
Different types of mold like different temperatures, and most grain molds like an 80ºF temperature, so Hellevang says that is not the temperature desired for grain storage. Cooling it will enhance the storability. Storability is determined by temperature and moisture and the higher that both may be, the shorter the storability of the grain. Dry, cool grain can be stored for more than 300 days, but 30% moisture corn at 70º and 80º temperatures may spoil within 1-3 days.
Storability can also be determined by the amount of cracked and broken grain which enhances mold growth, since the spores can grow on a more nutritional surface than the outer hull of the corn kernel. Hellevang also says test weight indicates immature kernels, which will also spoil more quickly.
When grain is stored in a bin, Hellevang says temperatures and moistures will be in motion even though nothing is physically happening in the grain. The cool sides of the bin will create a downward flow of air, which eventually pushes upward through the middle. The moisture will reach the top middle of the bin, the moisture will condense in the center, and create the potential for spoilage at the top center of the bin. A 3,000 bushel bin will not be much of an issue, but a 10,000 bushel bin will have enough of the temperature and moisture dynamics to create a spoiled crust at the top of the bin, which requires an aeration system to cool the grain while outdoor temperatures are cooling.
Conversely, while outdoor temperatures are rising in the spring and summer, grain at the sides of the bin will move warm air up, pulling cool air down through the middle of the bin. There will be moisture being pulled down from the top of the grain, to a level 2-4 feet below the surface, which will create a crust level at the top of the bin.
Grain is an insulator and will stay warm unless a cooling system is used. Despite sub freezing air temperatures, the grain mass will remain warm and moist and enhance the opportunity for spoilage and insect activity. When bins are being filled, temperatures are right for insects and spoilage, and that is a time when aeration is needed to reduce temperature. Hellevang says insect activity is reduced between 50º and 70º, and they become dormant below 50º, and insects are killed below 20-25º. To enhance storability during the spring, aeration needs to introduce warmer outside air, but Hellevang says it needs to remain in the 35-40º range from April through July.
Temperature on the side of the bin can be significant, even over the winter, because of solar radiation. Hellevang says that will change the temperature dynamics of the grain and necessitate aeration to preserve the quality of the grain. Spring and summer temperatures, caused by solar radiation, can aggravate an already bad situation.
There is not a best airflow rate, says Hellevang, but there is a length of time for the fan to be running to change the temperature of the grain in the bin. He says there is a common misconception that grain can be dried with aeration, which he says would take an inordinately long time to dry grain, but a much shorter time to cool it. Even with humid air outside, only a minor part of the bin would be re-wetted. It does not take a large fan to cool the grain.
When operating a fan at or below freezing, then ice will accumulate on vents on the bin, and could entirely seal the bin. When that happens, pressure inside will damage the roof. The access point on the roof should be left open. During times of snow, rain or fog, the recommendation is turning the fan off in highly humid conditions. Fans should be covered when not in use. Air can move through the fan and into the bin along with rodents and other pests and deteriorate the grain.
More corn is being stored into the spring and summer, and to limit insect problems, the fan should be operated periodically to cool down the grain at the top of the bin. If top three feet only need to be cooled, it would take only 11 hours of aeration to cool the grain, which is done best early in the morning. Head space should also be ventilated during the summer because of hot air. Heat can be removed with fans and vents similar to those used in an attic.
The grain should be constantly monitored for temperature, smell, and insects and be physically examined every 2 weeks until cooled, then on a regular 2 week schedule while stored. An infestation can occur within a month. Monitoring the amount of carbon dioxide in the air is important because spoilage and insects will release more carbon dioxide. Temperature can be measured with a grain cable that will help indicate what is occurring. But it will only indicate what is happening adjacent to the temperature sensor.
While poly bags have become popular, they do not prevent insect infestation or mold growth. Spoilage will occur if grain is wet and insects are reproducing. The temperature in the tube will follow the air temperature, but once it warms in the spring, the grain needs to be dry.
Summary:
Stored grain is a valuable asset, but there are simple actions that can be taken to ensure your grain value remains at a high levels. Aeration can lower the temperature and reduce the opportunity for mold growth and insect infestation. Temperature of the grain should be monitored every 2 weeks with a physical check of the grain to ensure it is in good condition. Air and moisture will move through the grain in the winter and summer as the outside of the bin cools and warms, creating the potential for spoilage were moisture condenses on grain.
Posted by Stu Ellis on 09/29 at 12:00 AM | Permalink
Comments
Posted by: Kyle O'Brien at November 23, 2011 10:10AM
Great read. Managing grain levels can be a delicate process sometimes. Trying to account for changes in the weather, making sure the moisture levels aren’t uneven inside the bin and tracking the sustainability of practically everything related to the bin is a chore. I’ve added a regulating grain system to help control all these areas. A lot of times what will happen is I’ll get analytics sent back from the software letting me know exactly how each section is doing, yearly feedback to prep next year’s grain output and so on.