November 14, 1997

Rewetting may be option for dry stored soybeans

The dry condition of some of the soybeans harvested this fall has prompted some interest in adding moisture to the beans before selling them. The moisture content normally used for trading soybeans is 13 percent, notes Bill Wilcke, engineer with the University of Minnesota Extension Service.

When soybeans are delivered to a buyer, the total weight is divided by 60 pounds per bushel to calculate the number of bushels. If soybeans are delivered to a buyer at a moisture content below 13 percent, the number of bushels is not adjusted upward to a 13 percent moisture basis, says Wilcke. This means the amount sellers are paid is less than they would receive if the beans were at 13 percent moisture. This also means that sellers have an incentive to rewet dry beans to 13 percent moisture.

"It is definitely illegal to add liquid water to any grain or oilseed to increase moisture content, and weight, for sale," says Wilcke. "But federal agencies have recently ruled that it is not illegal to force humid air through a crop to increase moisture content."

One way to rewet soybeans is to use a humidistat to control a fan that moves outdoor air through beans in a bin. "It appears that for typical Midwestern fall temperatures, if your target moisture is 13 percent, the humidistat should be set to turn the fan on when the relative humidity exceeds about 70 percent," says Wilcke. "However, if the fan operates much above 70 percent, soybeans will rewet to levels well above 13 percent. Soybeans can be safely stored through the winter at 13 percent, but they are likely to mold during warm weather if the moisture is much above 13 percent."

Wilcke cites a study at Purdue University in which researchers used relatively high airflow (0.5 to 1.0 cubic feet of air per minute per bushel of beans) to rewet some 10 percent moisture beans. The researchers were able to increase the weight of the beans enough to more than compensate for the cost of electricity to run the fans. But they ended up with one-third of the beans too wet and two-thirds of them still at their initial moisture. This means that ability to mix the beans would be essential for successful storage and marketing.

Since soybeans swell when they absorb moisture, Wilcke says it seems possible that rewetting beans could damage bins. "Using a vertical stirring auger to mix layers of dry and wet beans might be one way to reduce pressure generated during wetting," he points out.

If you do try to rewet soybeans, Wilcke offers the following tips for increasing chances of success:

• If possible, use a negative pressure system that pulls air down through the soybeans. This will keep fan heat from working against you, and it will leave the rewet beans at the top of the bin. There you can more easily monitor their condition and can more easily remove them from the bin, if necessary.
  
  
• After you've rewet a layer of beans, use a vertical stirring auger, or move the beans to mix the wet and dry layers.
  
  
• Use timers, humidistats, programmable controllers, or some type of automatic control to limit fan operation to weather conditions that will cause rewetting. If you don't have the ability to mix dry and wet layers, it also might be necessary to add a control that stops the fan during weather conditions that rewet beans to moisture levels that are too high for safe storage.
  
  
• Keep rewet beans cool (20-30 degrees Fahrenheit is the suggested winter storage temperature in the upper Midwest) to reduce chances of spoilage.
  
  
• Watch carefully for signs of moldy beans and for excessive stress on the bin.

An information sheet written by Wilcke on Considerations for Rewetting Soybeans contains additional details. Copies of the information sheet are available through county offices of the University of Minnesota Extension Service.

Wilcke is a faculty member in the university's College of Agricultural, Food, and Environmental Sciences.

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Source: Bill Wilcke, (612) 625-9733
Editor: Joseph Kurtz, EDS, (612) 625-3168, pkurtz@extension.umn.edu

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