Soybean handling and storage
Soybeans are usually traded on a 13 percent moisture basis, so it is to the farmer's advantage to harvest, store, and sell soybeans as close to 13 percent moisture (wet basis) as possible. Soybeans that are wetter than 13 percent moisture are likely to mold under warm conditions and buyers usually apply shrink factors and drying charges when wet beans are delivered.
On the other hand, soybeans that are drier than 13 percent moisture are more likely to split during handling and since they weigh less, fewer bushels are available for sale. If the storage temperature is kept below about 60 degrees Fahrenheit, soybeans can usually be held for at least six months at 13 percent moisture without mold problems.
For storage under warmer temperatures or for storage times longer than six months, however, the recommended moisture content is 11 percent.
Soybeans that are harvested at 11 to 13 percent moisture can be placed directly into ordinary storage bins equipped with simple aeration systems (perforated ducts or pads and relatively small fans). The suggested winter storage temperature for grains and oilseeds in the upper Midwest is 20 to 30 degrees.
Since soybeans are usually harvested at temperatures well above 30 degrees, it is necessary to cool them by operating aeration fans during cool weather. Rather than waiting until outdoor temperatures drop to 20 to 30 degrees before cooling stored beans, it is best to cool them in 10 to 20 degree stages as average temperatures drop in the fall.
For example, if beans are harvested at 55 degrees, you could wait a few weeks until average outdoor temperatures drop to 40 degrees and run the fans long enough to cool all the beans in the bin to 40 degrees. Then shut the fan off for a few more weeks and repeat the cycle when average outdoor temperatures fall to about 25 degrees.
When you are operating aeration fans to cool beans that are 11 to 13 percent moisture, you don't need to worry too much about relative humidity. Beans near the point where air enters the bin will rewet during very humid weather and some overdrying will occur during very dry weather, but if fans are operated no longer than necessary to cool the bin, overall moisture change will be quite small.
percent It takes about 50 times as long to change the moisture of a crop as it does to change its temperature, which means you can move a temperature front through 50 feet of beans by the time you've changed the moisture of a one foot layer.
Once soybeans have been cooled to 20 to 30 degrees, check them every two to four weeks during winter months to make sure that the temperature is stable and that no mold, insect, and crusting problems are developing.
If you find problems, or if bean temperature has moved above or below the desired range, operate the aeration fan during 20 to 30 degree weather to run a temperature front through the bin. If you need to hold the beans into spring and summer, increase your frequency of checking the bins to once a week, but unless a problem develops, it is not necessary to operate the aeration fans.
If you do need to aerate during spring or summer, do so during the coolest weather available and make sure that you keep bean temperature less than 60 degrees.
When spoilage problems develop in stored beans, they often start in pockets of accumulated fines (small pieces of broken seeds, weed seeds, and stem material) and foreign material. This material is difficult to aerate and it is often wetter and more susceptible to mold growth than are whole seeds.
Try to keep fines and foreign material out of the bin by setting combines for maximum cleaning or by running beans through a grain cleaner on the way into the bin. Or at least prevent the fines and material from accumulating in one spot by using grain spreaders to fill bins, by frequently moving spouts during bin filling, or by coring bins (removing some beans through the center unloading sump) after they are full.
For more information about grain and oilseed storage, obtain Management of Stored Grain with Aeration, AG-FO-1327, from the University of Minnesota (U of M) Distribution Center, or Crop Storage Management, AE-791, from the North Dakota State University (NDSU) Distribution Center. Both are available at all of the finer Extension offices.
You can also, contact me at the Polk County office in McIntosh at 800-450-2465, or at the Clearwater County office on Wednesdays at 800-866-3125. If e-mail is your thing, contact me at firstname.lastname@example.org.
Source: Ken Hellevang, NDSU Agricultural and Biosystems Engineering Department.