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Storing, Drying, and Handling Wet Soybeans

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By Lizabeth Stahl and Bill Wilcke

Extension Educator - Crops and Extension Agricultural Engineer

 

Soybean moisture levels of 16 to 20% or more at harvest have been reported throughout the state as this challenging harvest season continues.  If storage temperatures are below about 60F, soybeans at 13% moisture can usually be kept for about 6 months without having mold problems.  At a higher moisture content, how long can soybeans be stored before mold becomes a concern? 

 

Bill Wilcke, Extension Engineer with the University of MN, reports that as a guideline, soybeans in storage tend to act about the same as corn that is 2% greater in moisture content.  For example, soybeans at 16% moisture could be expected to act like corn at 18% moisture.  

 

The following table was developed for corn so to adjust for soybeans, simply look at the column for a moisture content 2 percentage points greater than the content of the soybeans in question.  For example, 18% moisture soybeans (look at the column for 20% moisture corn) at a temperature of 50F could be stored for about 63 days before there would be enough mold growth to cause price discounts or feeding problems.  Note that aeration is always recommended with all storage facilities.    

 

Allowable Storage time (days) for shelled corm (this is the approximate number of days corn can be held before there is enough mold growth to cause price discounts or feeding problems). 

Corn
temperature
(degrees F)

Moisture content (% wet basis)

 

16

18

20

22

24

26

20

3820

1459

722

427

287

212

30

1700

648

321

190

127

94

40

756

288

142

84

56

41

50

336

128

63

37

25

18

60

149

57

28

16

11

8

70

83

31

16

9

6

5

Reprinted from:  Natural-Air Corn Drying in the Upper Midwest, William Wilcke and R. Vance Morey, WW-6577-GO, 1995. http://www.extension.umn.edu/distribution/cropsystems/DC6577.html

 

Artificial drying of soybeans will be needed if soybeans are harvested and stored at a moisture content greater than 13%.  The article "Soybean Drying, Handling, and Storage" by Bill Wilcke, Vance Morey, and Ken Hellevang http://www.soybeans.umn.edu/crop/harvest/index.htm discusses recommended options and guidelines, and is recommended reading if you are needing to dry soybeans.  The bulletin  "Natural-Air Corn Drying in the Upper Midwest" by Bill Wilcke and Vance Morey, http://www.extension.umn.edu/distribution/cropsystems/DC6577.html,  is also useful as many of the principles for drying corn will be similar for drying soybeans. 

 

The soybean drying article, the natural-air corn drying bulletin, and some other post-harvest information can be found on the post-harvest website.

 

Ken Hellevang, NDSU Agricultural Engineer, just released an article on soybean drying and storage advice on 10/20/2009, and rather than re-word what he has already said well, his article is attached below in its entirety, with his permission. Remember that this article was written for a northern location. In southern MN, natural-air drying usually works for about two weeks longer - until about December 1.

 

NDSU Offers Soybean Drying, Storage Advice

NDSU's grain-drying expert offers tips on drying and storing soybeans.

A challenging soybean harvest is creating many questions related to storage and drying, according to Ken Hellevang, agricultural engineer with the North Dakota State University Extension Service.

Soybeans at 11 percent moisture have similar storage characteristics to wheat or corn at 13 percent moisture, so an allowable storage time chart for cereal grains can be used to estimate allowable storage times for soybeans. For example, soybeans at 18 percent moisture content would be similar to cereal grains at 20 percent moisture, so soybeans would be expected to have an allowable storage time of about 50 days at 50 degrees. The allowable storage time is reduced to 25 days at 60 degrees and extended to about 90 days at 40 degrees.

The amount of natural air drying that will occur in late October and November is limited. The equilibrium moisture content of soybeans for air at 40 degrees and 70 percent relative humidity is 13.5 percent. An airflow rate of 1 cubic foot per minute per bushel (cfm/bu) is expected to dry soybeans with 18 percent moisture in about 70 days. Adding supplemental heat to raise the air temperature by 5 degrees will permit drying the soybeans to about 11 percent moisture in about 55 days.

Only about one-half of the beans would be expected to dry by mid-November, when outdoor temperatures become too cold to dry efficiently. Adding heat would cause the beans on the bottom of the bin to be dried to a lower moisture content and it would increase drying speed only slightly. Cool the soybeans to between 20 and 30 degrees for winter storage and complete drying in the spring. Hellevang recommends starting to dry when outdoor temperatures are averaging about 40 degrees.

Increasing the airflow rate will increase the drying speed. However, the fan horsepower required to achieve the higher airflow rate becomes excessive unless the grain depth is very shallow. For a soybean depth of 22 feet, the rule of thumb is that each 1,000 bushels of soybeans will need fan horsepower of about 1. Achieving an airflow rate of 1.5 cfm/bu will require about 2.5 horsepower and an airflow rate of 2 cfm/bu will need about 5 horsepower.

The type of fan greatly affects the airflow provided per horsepower, so use a fan selection software program such as the one developed by the University of Minnesota. It is available on the NDSU grain drying and storage Web site at http://www.ag.ndsu.nodak.edu/abeng/postharvest.htm. You also can use the chart for your fan that shows the amount of airflow delivered at various static pressures.

Soybeans can be dried in a high-temperature dryer, but the plenum temperature needs to be limited to minimize damage to the beans. Refer to the manufacturer's recommendations for maximum drying temperature. Typically the maximum drying temperature for nonfood soybeans is about 130 degrees. Even at that temperature, some skins and beans will be cracked.

One study found that with a dryer temperature of 130 degrees, 50 percent to 90 percent of the skins were cracked and 20 percent to 70 percent of the beans were cracked. Another study found that 30 percent of the seed coats were cracked if the drying air relative humidity was 30 percent, and 50 percent of the skins and about 8 percent of the beans were cracked at 20 percent relative humidity.

The relative humidity is reduced by one-half for each 20 degrees that the air is warmed. Therefore, if air at 40 degrees and 80 percent relative humidity is warmed to 60 degrees, the relative humidity is reduced to 40 percent, and if it is heated to 80 degrees, the relative humidity is reduced to 20 percent. Monitor the amount of damage occurring during drying and regulate the plenum temperature to obtain the acceptable amount of damage.

Food soybeans and seed beans must not have damage to the seed coat, so natural-air or low-temperature drying is the preferred drying method, Hellevang says.

Source:  Ken Hellevang, (701) 231-7243, kenneth.hellevang@ndsu.edu, Editor:  Ellen Crawford, (701) 231-5391, ellen.crawford@ndsu.edu.

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