Peanut processing
Practical Action
Pests and disease
Groundnuts are attacked by; the Bean leaf roller (Lamprosema indicata), Leafminern
(Stornopteryx subsecivella), Long-horned grasshopper (Phaneroptera furcifera), Cotton leafhopper
(Empoasca biguttula), Slant-fac grasshopper (Atractomorpha psittacina), June beetles
(Leucopholis irrorala), and Tiger moth caterpillar (Dasychira mendosa) amongst others.
Mould (Aspergillus flavous) can attack groundnut, leading to aflatoxin contamination, if the nuts
are not dried sufficiently. Aflatoxin in peanuts is a serious problem. The peanuts can become
infected either before or after harvest. Once they are infected, there is no way that the aflatoxin
can be removed and the peanut becomes dangerous for consumption. If the peanut is free from
the disease at harvest, correct drying can prevent later infection. Some aflatoxin infection can
be visible to the eye as mould, but in other cases it cannot be seen. Laboratory tests need to be
carried out to confirm the presence of aflatoxin. The recommended moisture level should be less
than 10 percent.
Blanching is a process that destroys enzymes (biological compounds that are responsible for
deterioration and off-flavours in foods after harvest), while retaining the colour and most of the
nutritional value. It is a very simple process and basically involves the immersion of the
foodstuff in boiling water or steam for a very short time, followed by rapid cooling by plunging in
very cold water. To carry out this process at the small scale all that is required is a large tank in
which water can be boiled. At a slightly higher level, there is specific blanching equipment
available- both water and steam blanchers.
Oil extraction
Oil contains high amounts of energy and fat-soluble vitamins (A, D, E, and K) and essential fatty
acids. The oil content of the kernels is between 45% and 55%.
The peanuts are prepared for the oil extraction process by being shelled and cleaned. Oil
production requires some type of press with which to extract the oil form the groundnuts and
filtering equipment.
Practical Action has developed a simple manual screw press that would be suitable for extracting
oil from peanuts, as well as many other agricultural crops. There are quite a number of presses
of very similar design, they are simple to make, except for the screw which would have to be
machined.
For more information see the Practical Action Technical
Brief Principles of Oil Extraction.
Peanut butter
The peanuts are first shelled and cleaned. They are then
roasted at 425°F (218°C) for 40-60 minutes either a) on
trays in an oven, the nuts being turned by hand from time
to time or b) in equipment similar to that used for roasting
coffee. This small rotary roaster allows each nut to
become uniformly roasted.
After roasting the nuts will be well browned and the skins
loose. After cooling, it is necessary to remove the skins by
gentle brushing, an inspection will allow the manual
removal of discoloured and other rejected
material.
2
Figure 2: Peanut grinding
machine. Example of equipment
produced in the Practical Action
light engineering workshop.
©Practical Action