September 01, 2003
You can use bins on the farm to store dry
beans, but you must manage them carefully.
With the right equipment and know-how you can store dry beans on the farm, says Ken Hellevang, NDSU extension agriculture engineer. He offers the following information:
Edible beans can be stored at 18% moisture content during the fall and winter if they are cooled with an aeration system so they are no warmer than 50¡F in October and 30¡F degrees in November.
Lower moisture contents should be used if longer storage periods are desired or the beans cannot be cooled to the specified temperatures. Beans at 16% moisture are expected to store for about nine months at 60¡F, which is the basis of the 15.5% moisture content recommendation during fall through spring. A moisture content of 16% should normally be considered the maximum recommended short term storage moisture content for edible beans.
For long-term storage the moisture content must be low enough to permit storage without deterioration at typical summer temperatures. For example, the recommended long-term storage moisture content for wheat is normally at about 13%. This keeps the relative humidity in the wheat below 65% at 70 degrees, which limits mold growth. The recommendation for edible beans is also about 13% based on the same considerations.
If the beans can be kept cooler, the acceptable moisture content can be increased. If the beans can be kept at 60¡F or cooler, the moisture content can be 14% for long-term storage.
It is important to follow good storage management practices such as measuring the temperature and moisture content of the beans at least monthly. Whenever there is more than a 10 degree difference between the average outdoor temperature and the bean temperature during the fall, the beans should be cooled with aeration. This should continue until beans at 16% moisture are cooled at least to 40¡F and 18% moisture beans are cooled to about 30¡F. Cooling below 30 degrees is not necessary and may increase the potential for handling damage.
Edible beans require special care when drying with a high temperature column dryer. The relative humidity of the drying air should not be lower than about 30% when drying Navy beans. Normally the drying should occur with the air heated less than about 20¡F above the outdoor air temperature, to keep the relative humidity above 30%. The beans need to be monitored continuously to assure that the beans are not being damaged. Other beans are best dried with no supplemental heat.
Natural air drying will work well for drying edible beans during mid-September to mid-October in North Dakota. Based on average climactic conditions the beans should dry to about 14% moisture. Shutting fans off during the warmest part of the day will raise the final moisture content but lengthen the drying time. Shutting fans off during periods of higher humidity, such as night, will reduce the final bean moisture content. Recommended minimum airflow rates for various moisture contents and the corresponding estimated drying times are shown in the following table.
Minimum recommended airflow rates and estimated drying times for dry edible beans using a natural air drying system from mid-September to mid-October in North Dakota are:
Moisture Content Airflow Rate Drying Fan Time
cfm/bu cfm/cwt days
22% 2.5 4.2 23
21% 1.6 2.7 30
2.0 3.3 24
20% 1.5 2.5 28
2.0 3.3 22
19% 1.5 2.5 28
2.0 3.3 22
There is no information available on the static pressure associated with moving air through edible beans, so design the drying system using the data for shelled corn.
Dry edible beans are fragile, so they must be handled with care. Beans become more susceptible to handling damage at lower moisture contents and cold temperatures. Do not warm beans above 50 degrees, since allowable storage time is reduced by about 50% for each 10 degree temperature increase. Belt conveyors are preferred due to their gentleness in conveying. Drop heights must be limited. A bean ladder should be used inside storage bins to reduce impact damage. The speed of auger rotation should be reduced and augers operated "full" to minimize damage. Elevator legs need to be adapted for handling beans, including reducing the discharge velocity and utilizing a method of gently slowing the beans at the bottom of spouts.
For more information, request the following publications from your NDSU County Extension Agent: AE-701 Grain Drying, AE-791 Crop Storage Management , EB-35 Natural Air - Low Temperature Crop Drying or find them on at www.ext.nodak.edu/extpubs/