According to Shawn Shouse, ISU Extension Ag Engineering Program Specialist, the short answer is this:
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Harvest works best (least damage) with beans 13-15% moisture.
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Safe storage moisture is 13% for just through the winter, 12% for into next summer, and 11% for a year or more.
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With a full aeration floor in the bin, beans up to 15% can probably be dried with a small aeration fan, beans up to 17% can probably be dried with a big drying fan (no added heat).
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Heated drying can be done with caution. Don’t raise drying air temperature by more than 20 degrees and don’t get drying air below 45% relative humidity.
Here are some links to good information:
News article by Charlie Hurburgh
/CropNews/2009/1019hurburgh.htm
Soybean Drying and Storage bulletin
/Publications/PM1636.pdf
Soybean storage and drying tips website
http://extension.agron.iastate.edu/soybean/production_storagetips.html
Grain Drying & Storage: Bill Wilcke's website at the University of Minnesota (at the bottom of the web page it contains links to several other good websites): http://www.bbe.umn.edu/Post-Harvest_Handling_of_Crops
http://www.ag.ndsu.nodak.edu/abeng/postharvest.htm
For information on Natural Air Drying, see:
http://www.extension.umn.edu/distribution/cropsystems/DC6577.html
For information on soybean drying,
http://www.soybeans.umn.edu/crop/harvest/
If you have further questions, please feel free to contact either of the following: