For safe storage, peanuts are dried to below 10.50% moisture.
Otherwise, if not properly dried, peanuts are susceptible to
growth of molds such as aspergillus flavus which may produce
aflatoxin, a carcinogen that can cause cancer when consumed
in sufficient amounts. Currently, decision support systems
for peanut drying operations require heavy user interaction
including sampling the peanut pods for kernel moisture tests
and updating any changes in atmospheric conditions. The
main parameter in peanut drying is the peanut kernel moisture
content. Usually, kernel moisture testing is done every
three hours with an official moisture meter which requires the
peanut pods to be shelled. A drying monitoring unit (Fig. 6 and
Fig. 7) integrating all of the environmental sensors and a microwave
moisture sensor for in-shell peanuts was developed,
calibrated in the laboratory, and tested in the field in drying
wagons and trailers. The microwave moisture sensor has the
same design and measurement principle used for flowing
grains (Fig. 3) and a benchtop moisture meter shown in Fig. 4.
The drying monitoring unit provides continuous monitoring
of environmental conditions and kernel moisture content with
little interaction from the operator and could cut off the heaters
for the driers when hot-air drying is not beneficial. This makes
the drying more efficient and results in significant energy savings.
It was estimated that US$22,000 in energy savings per
buying point could be realized with such a system in a single
harvest season. Fig. 8 compares the moisture testing results obtained
with the microwave moisture sensor to those obtained
with the official meter. A large difference was observed at the
beginning of the drying process between the two, but their
readings converged at the end of the drying period. This is explained
by the fact that the official meter was calibrated with
well equilibrated samples for moisture close to the value of
10.49% (Fig. 5), which is the maximum moisture content required
for sale of the peanuts