Maintaining Grain Quality During Long-Term Storage
Some grain will be stored for many months or even more than a year due to low grain prices. Maintaining grain quality during this extended storage will require extra care and management, according to North Dakota State University's grain storage expert.
"Grain that will be stored for an extended time needs to be good quality grain," says NDSU Extension Service agricultural engineer Ken Hellevang. "The outer layer of a grain kernel is the pericarp, or seed coat, and provides protection for the kernel. If the pericarp is damaged, the kernel is more susceptible to mold growth and insect infestations. This reduces the expected storage life of the grain."
Broken kernels and foreign material should be removed by cleaning the grain before storing it. Segregation based on size and density occurs as grain flows into storage. Fines accumulate in the middle unless a functioning distributor spreads them throughout the grain. Unloading some grain from the center of the bin will remove some of the fines and help level the grain in the bin.
Also, immature kernels have a much shorter expected storage life. Grain test weight may be an indicator of maturity and storability.
Assure that the storage facility is clean and insects are not living in aeration ducts, under perforated floors, or in handling equipment or debris around the facility. Fumigate the empty bin to kill insects under the floor or in aeration ducts if an infestation occurred during the previous year. Also, consider applying an approved residual bin spray and a grain protectant to repel potential insect infestations if storing grain during warmer portions of the year.
Managing Moisture in Stored Grain
Mold growth requires moist conditions, usually above about 70% relative humidity, and warm temperatures. To reduce the potential for mold growth, the grain moisture content should be below the equilibrium moisture content (EMC), at 60% to 65% relative humidity.
The EMC of corn at 70 degrees and 65% relative humidity is about 13.5%, and at 50 degrees, the EMC is about 15%. If you can keep stored corn below 50 degrees, you can store it at 15% moisture. But if the temperature will be warmer, then the recommended storage moisture content is about 13.5%. Equilibrium moisture content charts for various types of grain are available on the internet.
Grain going into long-term storage should be dried and cooled rapidly after harvest. The allowable storage time (AST) is an estimate of the life of the grain until it has deteriorated enough to affect grain quality. Grain AST charts, such as those in the publications section of the NDSU grain drying and storage website, are available online.
Managing Temperature in Stored Grain
The AST is cumulative, so if one-half of the storage life is used before the grain has been dried and cooled, only about one-half of the life is available for the drier grain. For example, corn stored at 20% moisture and 50°F has an AST of about 50 days. If it is dried to 15% after 25 days and cooled for winter storage, but warms to 70°F next summer, the AST at 15% and 70°F is only about 60 days, rather than the 125 days shown in an allowable storage time chart.
"Controlling grain temperature is critical for maintaining grain quality," Hellevang says. "Insect reproduction is reduced below about 70 degrees, insects are dormant below about 50°F, and insects are killed if grain is below 30°F for a few weeks."
Moisture migration increases the moisture content at the top of the bin when about a 20-degree temperature difference occurs between the grain and average outdoor temperature. Therefore, the grain should be cooled with aeration when you have a 10- to 15-degree difference between grain and average outdoor temperatures. Cool the grain to 25 to 30°F in northern states and 40°F or cooler in southern states for winter storage.
The bin vents could ice over when the aeration system is operated near or below 32°F. Utilize a sensor to stop the aeration fan if bin roof pressures become excessive, or leave access doors open to serve as pressure relief valves if operating the aeration system near
freezing temperatures to reduce the potential for damaging the roof.
Steps to Ensuring Quality Long-Term Storage
Hellevang also has this advice for long-term grain storage:
- Check the grain at least every two weeks until it has been cooled for winter storage and every two to four weeks during the winter.
- Verify that the moisture content is at the recommended storage level.
- Check the grain temperature.
- Inspect for insects.
- Look for indications of storage problems such as condensation on the roof.
"Using temperature cables or sensors to monitor grain temperature is encouraged, but remember that because grain is a good insulator, the temperature can be different just a few eet from the sensor," Hellevang says.