Poor management of stored grain can result in spoilage and loss of market grade. Storing grain at the proper moisture content, making routine grain observations during storage, and grain temperature management are important to prevent grain storage problems.
Proper grain storage involves managing moisture content, temperature, and insect activity in storage structures. Poor temperature control is the main reason dry grain goes out of condition. Natural air movements that cause heat and moisture to accumulate in stored grain can be offset by the proper use of aeration.
Grain going out of condition prematurely in farm bins can result in damage discounts because of spoilage. Proper aeration, insect control, and regular, thorough observation are all necessary to maintain grain quality. If grain is stored at the proper moisture content, issues that arise can usually be attributed to improper grain cooling, inadequate observation, poor grain quality, or lack of insect control measures. Refer to Table 1 for the proper moisture content at which to store corn and soybeans. If grain coming out of the field is too wet, options for drying to reach the desired moisture content for storage should be considered. The primary reason that dry grain goes out of condition is due to poor temperature control which allows moisture to migrate through the grain, accumulate, and cause spoilage.
Temperature Control and Moisture Migration. During late fall and early winter throughout the Corn Belt, temperatures cool significantly. Falling temperatures cause grain and air along bin walls to cool. The insulated grain and air in the middle remains at around the same temperature as when it was binned. Temperature variances in different areas of the grain bin cause convection currents, the slow, natural flow of moisture and air. Convection currents occur because the cool outer air becomes heavier and settles. As it moves downward and inward, it becomes warmer and lighter causing air to rise through the center column of grain further warming the warm grain. The warmer air has increased moisture-holding capacity and it begins to absorb small amounts of moisture. As it moves upward, it again enters cool grain and some of the moisture from the air is left with the grain through condensation and diffusion. This process is called moisture migration – the most common cause of problems in stored grain. Check for crusting, wet, slimy grain, ice or frost accumulation and/or heating. Condensation or frost on the underside of roof, hatches, and vents on cold days almost always indicates a moisture migration problem. If crusting occurs, you should stir the surface to break up the crust or if severe, remove the spoiled grain.
Aeration Management. Regardless of the time of year, grain temperatures should be within 15 to 20 degrees of the average monthly temperature. Aeration is a process of forcing air through the grain either continuously or intermittently to affect the grain temperatures. While some minor moisture changes can occur with changing temperatures, aeration is not the same as drying grain. Aeration is used to cool grain in the fall, or help to warm it in the spring. Negative pressure systems move air down through the grain by suction from the bottom. Positive pressure systems force air upward through the grain. The area along which the temperature change follows through the grain mass is known as the cooling or warming zone. As the cooling/warming zone moves up through the bin in a positive pressure system, or down through the bin in a negative pressure system, the grain temperature within the zone is changing and the grain behind the zone has been tempered.
One cooling/warming cycle is the amount of time needed to move a cooling/warming zone completely through the bin (top to bottom in negative or bottom to top in positive). Once a cycle has begun, the fan should operate continuously until the zone moves completely through the bin. The time required for one full cycle depends on aeration airflow rate. Generally, two to three full cycles are needed to cool or warm grain to desired storage temperatures.
On-farm storage systems may be equipped to move air at between 1/10 cfm (cubic feet of air per minute)/bu to over 1 cfm/bu. The rate depends on bin type, air distribution system, desired storage moisture percentage, and proper management procedures. The time it takes to complete a full warming or cooling cycle depends on the aeration rate and time of year and can be figured with the following formulas by season: Fall hours = 15/(cfm/bu); Winter hours = 20/(cfm/bu); Spring hours = 12/(cfm/bu).
Cooling Grain for Winter Storage. In general, most growers will cool grain to 35-40° F for most of the Midwest; or below 35° F for colder average temperatures. The first aeration cycle should begin when the average daily temperature is 10-15° F cooler than the grain. Grain that has been dried at higher temperatures should be aerated immediately. Operate equipment long enough to complete the full aeration cycle to prevent spoilage; roughly a week depending on aeration rate. In a couple weeks, when the temperatures have dropped another 10-15° F, the full aeration cycle should be repeated. A maximum of three cycles are needed. If only two cycles are planned to reduce costs, the second cycle should be delayed until outside temperatures can help cool grain to 35-40° F. The exact number and length of cooling cycles depend on fan capacity, when and the temperature at which grain was binned, and how fast air temperatures cool during the fall.
It is important to know how long it will take the fan to move a cooling/warming cycle through the bin. If the rate is not known, contact the dealer where the fan was purchased. Once the rate is known, the number of hours can be figured by using the formula in the aeration management section. Ensure that the cooling/warming front moves completely through the bin as this reduces the chance that moisture will accumulate and cause spoilage. To check your bin to see if the cycle has completed:
Making sure the front has completed is MOST crucial during the final cycle. It is a good habit to record dates, times, and grain and air temperatures. The actual time should be checked with the amount of time you calculate. If it is taking longer than expected, airflow may be reduced or fines may be causing a blockage. Each time a cycle is run in the same bin with the same equipment, it should take about the same amount of time.
Observation and Management. Bins should be observed weekly during the fall and spring when temperatures are quickly changing. Bin checks can be reduced to every two or three weeks throughout the winter. Establishing a set day of the week and time of day to check may help make it easier to remember. Keep an eye on the surface conditions, temperatures, grain condition, and be mindful of different smells, both in the grain and exhaust air. Once grain is cooled, continue checking exhaust air for smells to indicate grain going out of condition. Regardless of the season or weather, if signs are of heating or hot spots are detected, run the fan continuously until no further heating can be detected. If hot spots cannot be remedied with aeration, you may have to remove the grain and clean, dry, or even sell it. It will likely be better to sell at a lower price than to allow an entire bin may go out of condition.
Insect Control in Stored Grain. Insect infestations can arise from residue in combines, handling equipment, and old grain left in storage. Preventative control measures before filling bins include cleaning equipment/bins and applying approved insecticides to clean bin surfaces. New grain should NOT be placed on top of old grain infested with insects.
Safety. The dangers of grain handling cannot be stressed enough. NEVER enter a bin when grain is flowing and be extremely cautious around all grain handling structures and equipment. Be sure to have safety precautions and emergency plans in place and make them known to all workers and bystanders on the farm.
McKenzie, B. and L. Van Fossen. 1995. Managing dry grain in storage. Midwest Plan Service. AED-20. Purdue University. www.extension.purdue.edu/extmedia; Pedersen, P. 2006.
Soybean storage tips. Iowa State University Extension. http://extension.agron.iastate.edu
Wilcke, W. and G. Wyatt. 2002. Grain storage tips. University of Minnesota FS-M1080, http://www.extension.umn.edu.
Web sources verified 10/2/2018