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Drying Dry Beans With Natural Air
Harvesting beans at moisture contents exceeding 16% to 18% minimizes bean damage such as cracking, provides more harvest flexibility, reduces harvest losses, and maintains bean color quality. Research was conducted to determine a natural-air drying system that would dry pinto beans to 15%-16% moisture. An airflow rate of about 2 cfm/bu. was used for the drying. The beans were cleaned prior to drying, because previous work showed that dirt in beans resulted in a dust on the beans after drying. The initial bean moisture content was about 25%. The drying fans were controlled by a humidistat set to shut the fans off if the relative humidity was below 60% to prevent over drying. The rain sensor shut the fans off if it rained more than 0.5 inch.
The beans at the bottom of the bins dried down to
about 15% first, and then the drying moved to the next stage while the moisture
content of the beans at the bottom of the bin fluctuated within a percentage
point for the remainder of the drying period. After about 132 hours the bottom
of the bin dried down to the desired moisture content.
It took about 520 hours before the middle of the bin dried down to 15%,
and about 830 hours to complete the drying of the beans at the top of the bin.
This is the actual hours of fan operation, which is different than calendar
days. Since a humidistat and rain sensor was used, the fans didn�t run all the
time, only during the desired relative humidity range of 60% to 100% and when it
was not raining.
The color quality, lightness and redness, of the beans was maintained during drying.
Figure 9.
Graph showing the drying progress in hours.
Kenneth Hellevang, Ph.D., PE
Extension Engineer, Professor
NDSU Extension Service
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