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United States Department of Agriculture

Agricultural Research Service

Post Harvest Research
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Post harvest research at the National Peanut Research Laboratory encompasses all aspects of peanut handling and processing from the time peanuts are dug and inverted in the field until they are unloaded from bulk storage and transported to a shelling facility.

Inverted peanuts in field

 Peanut storage warehouse  Curing facility

For more information on post harvest research contact Chris Butts.



Peanuts are approximately 40% moisture content when initially dug from the ground and inverted in windrows. They are threshed and harvested after the moisture content has fallen below 20%.  Curing continues by forcing heated air through the peanuts in wagons or semi-trailers equipped with a false floor and usually occurs at a facility curing between 50 and 200 individual loads at the same time.

 Trailers at curing facility  Drying wagons under cover

Engineers are conducting small scale research investigating dryer control methods to reduce curing time and energy requirements.

NPRL dryer control

Computer software (Expert Systems) developed by engineers at NPRL aids personnel in managing the commercial curing operation by predicting drying time, suggesting sampling schedules, and providing real time estimates of moisture content. The software also maintains a database of all peanuts cured at the facility for future operation management. PECMAN is available for download and installation at no cost.


For more information contact:


Farmer Stock Storage

After grading, peanuts are unloaded and stored in large warehouses until they are needed at the shelling plant for further processing and sale to a peanut product manufacturer.  Engineers have conducted research to determine proper ventilation and aeration rates. A tool is available to calculate warehouse capacity, dimensions, and headspace ventilation requirements for safe storage.

Peanut storage warehouse

Engineers are conducting research to look at new storage structures for farmer stock peanuts.  Aeration strategies and length of storage are being examined to determine the amount of aeration required in these monolithic concrete domes and the deterioration in quality over various periods of storage.

New peanut storage structure being tested

Peanuts produced according to USDA organic production standards, must be processed and stored separately from conventionally grown peanuts. Insect and rodent control in storage must be done according to organically sound practices using no chemicals. One such method may be the use of low oxygen atmospheres. Engineers at NPRL are investigating the use of hermetically sealed storage containers for farmer stock peanut storage. Peanuts are placed in these bags and sealed using a zipper closure. 

Hermetically sealed peanut storage container

The peanuts respire, consume the oxygen within the bag, and give off carbon dioxide.  The airtight bag allows no moisture or carbon dioxide to escape nor oxygen to enter resulting in a very low oxygen atmosphere.

Chart showing effectiveness of sealed container


For more information contact Chris Butts.


Grading and Quality Measurement

In-shell Peanut Moisture Measurement:

In-shell Peanut Moisture Measurement
1.  Impedance meter, 2. Cylinder with electrodes, 3. Computer

The impedance method will measure moisture content of peanuts without the need for shelling and cleaning the samples.  This could save time, labor and the wastage of samples used for testing.

Peanut Pod Brightness Measurement:

Optical reflectance measurement device

This optical reflectance measurement device determines the pod brightness of peanuts objectively, and is useful in the color classification of Valencia variety of peanuts.

NIR reflectance method for moisture content determination for peanuts:

NIR reflectance method for moisture content determination for peanuts

1.  Reflectance attachment and sample holder, 2. NIR spectrometer, 3.  Computer

A non-contact reflectance method is being developed using NIR methods to determine moisture, protein and oil content of peanuts rapidly and nondestructively.


For more information contact:


Last Modified: 1/22/2009