Peanuts or groundnuts are a high value crop that can be marketed with little processing but are extremely versatile and can be used in a wide range of products. The oil can be used for cooking, they can be used as a shortening or as a base for confectioneries and they can be used to make peanut butter.
There are two types of groundnut, a bush and a runner. Hybrids of the two varieties have been developed and are commercially available. The pods of the bush variety contain one or two kernels in a thin shell. The runner variety has one to three kernels in a thicker shelled pod.
Irrigation techniques consisting of regular watering up to ripening stage and then reduced to avoid wrinkling. Nitrogen fixing nodules are found on the roots although nitrogen and potassium fertilizers are often added to the soil to improve yields.
The groundnut plants are annually harvested by being pulled or dug up. This is usually called “lifting”. There are various designs of equipment available to assist in lifting groundnuts. The minimum equipment required would be a forge, anvil, hammer, tongs, chisel, and punch.
This is the process of removing groundnuts in-shell from the haulm after lifting and, usually, drying. This is normally done by hand and is a tedious and time consuming operation. The pods are removed by picking or flailing.
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-flavors in foods after harvest), while retaining the color 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 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.
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 discolored and other rejected material.
A simple winnower to remove the skin from the nuts can be made by allowing the nuts to fall in a gentle stream in front of an electric fan. The Heavy nuts will fall straight down while the lighter skin will be blown away.
Traditionally women pounded the nuts between stones, a very time consuming activity. Now nuts are often ground in a mill that may be powered by hand or with a motor. The type of mill used will depend on the scale of production, The most commonly used mill is an adjustable plate mill. The tighter the distance between the plates the finer the texture of the butter. The milling process may have to be repeated to obtain the desired texture. (Photo above is the example of peanut grinding machine.)
Salt may be added at this stage; about 2% by weight. A special anti-oxidant chemical may be added to prevent rancidity, which will develop after a few months. However, to start with the product will probably by sold very soon after manufacture. The peanut butter is then packed in jars.
The type of peanut butter produced by this process is of the ‘crunchy’ variety, and adjustments on the mill can produce varying textures. For the very smooth paste a more sophisticated milling process is required, with the high levels of heat being produced during milling causing difficulties.
To avoid separation of the oil and the settling out of the solids within the peanut butter after few days of storing, the stabilizer called glyceryl monstearate (GMS) can be added to the at 2-3% by weight. It is suggested that all of the GMS is added to a small amount of the peanut butter to form a premix and then this is mixed into the main batch. This results in more even distribution of the small amount of GMS in the batch