NEWS for North Dakotans
Agriculture Communication, North Dakota State University
7 Morrill Hall, Fargo, ND 58105-5665

September 3, 1998

Ag Engineer Offers Tips for Drying, Storing, and Handling Soybeans

Keeping soybeans in top condition requires proper drying, storage and handling, notes a North Dakota State University agricultural engineer.

"Getting a good quality crop out of the field is only the first step," says Ken Hellevang of NDSU's Extension Service. "Soybeans are susceptible to a great deal of damage if they're not handled properly."

Maximum moisture contents for safe storage of soybeans that are aerated to keep them cool is 14 percent for storage over winter, 12 percent for storage up to one year, and 11 percent for long-term storage, Hellevang says. Most markets will discount soybeans exceeding 13 percent moisture.

Initial moisture content does not affect the amount of cracked or split beans, but drying temperature and speed of drying does affect the amount of damage occurring, he says.

"Drying temperatures need to be limited. Research shows that increased drying temperature leads to major soybean damage," Hellevang notes. And avoid dryers which recirculate the soybeans while drying. This additional handling tends to increase damage.

The maximum recommended drying temperature for commercial (non-food) soybeans is about 130 F for continuous flow dryers, 110 F for batch dryers, and 110 F when drying seed.

If seed-coat quality is important, keeping the relative humidity of the drying air above 40 percent limits the amount of damage. At 40 percent relative humidity (RH), about 15 percent of the seed coats were damaged in a research study. At 30 percent RH, the damaged increased to about 30 percent, and at 20 percent RH the amount of seed coat damage increased to about 50 percent. Warming air by 20 F reduces the relative humidity by half. For example, air at 50 F and 80 percent RH will have a relative humidity of about 40 percent after being heated to 70 F.

"It doesn't take much heat to bring relative humidity below 40 percent," Hellevang notes. "The combination of heat and humidity has to be monitored very closely."

Hellevang says it's best to harvest soybeans early and do natural air and low temperature drying during October if possible. Soybeans will dry to about 13.5 percent moisture in 20 to 30 days with adequate airflow and normal October conditions in North Dakota. In November, soybeans will only dry to about 15.5 percent moisture, and the drying time will be about twice as long due to colder air temperatures. Adding supplemental heat to warm the air by 5 F will cause the beans to be dried to about 11.5 percent moisture. The drying time will still be longer than in October due to lower air temperature.

Minimum airflow rates of 1 cubic foot per minute per bushel (cfm/bu) to dry soybeans at 16 percent moisture, or dryer, soybeans, and 1.25 cfm/bu for up to 18 percent moisture beans are recommended. The expected drying time is about 20 to 30 days at these airflow rates. The resistance to airflow is about 25 percent less through soybeans than it is through corn, so it is easy to obtain these airflow rates. Static pressures will be much lower than occurs when drying small grains, so an axial flow fan will likely deliver the most airflow per horsepower. About 1 to 1.5 hp per 1,000 bushels of beans is required for drying, depending on bean depth and airflow rate desired.

"Soybeans are subject to splitting during handling, so handle them gently," Hellevang advises. Belt conveyors, bucket elevators, and drag or mass conveyors provide the gentlest handling. Normal grain augers can be used if operated slow and full, and pneumatic conveyors can be used if the air-to-grain ratio is properly set and lines are laid out with a minimum number of very gradual curves. To minimize damage during handling reduce drop heights, and do not handle very cold grain. Many times damage that appears to occur during handling was actually caused during drying and is exposed during handling.

Soybeans should be cooled to 20 F to 30 F for winter storage. Check the soybeans every two weeks until cooled to about 25 F and then check at least monthly for changes that indicate storage problems.

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Source: Ken Hellevang (701) 231-7243

Editor: Tom Jirik (701) 231-9629

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