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cashew tree is evergreen. It grows up to 12 meters high and has a spread of 25
meters. Its extensive root system allows it to tolerate a wide range of moisture
levels and soil types, although, commercial production is advisable only in well-drained,
sandy loam or red soils. Annual rainfall needs to be at least 889mm (35 inches)
and not more than 3048mm (120 inches). Cashew trees are most frequently found
in coastal areas.
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main commercial product of the cashew tree is the nut. In the main producing areas
of East Africa and India, 95% or more of the apple crop is not eaten, as the taste
is not popular. However, in some parts of South America and West Africa, local
inhabitants regard the apple, rather than the nut kernel, as a delicacy. In Brazil,
the apple is used to manufacture jams, and soft and alcoholic drinks. In Goa,
in India, it is used to distil cashew liquor called "feni".
The
cashew fruit is unusual in comparison with other tree nuts since the nut is outside
the fruit. The cashew apple is an edible false fruit, attached to the externally
born nut by a stem. In its raw state, the shell of the nut is leathery, not brittle.
It contains the thick vesicant oil, CNSL, within a sponge-like interior. A thin
testa skin surrounds the kernel and keeps it separated from the inside of the
shell. The primary products of cashew nuts are the kernels which have value as
confectionery nuts. Cashew nut shell liquid (CNSL) is an important industrial
raw material for resin manufacture and the shells can be burned to provide heat
for the decorticating operation.
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extraction of the kernel from the shell of the cashew nut has been a manual operation.
The nut is roasted which makes the shell brittle and loosens the kernel from the
inside of the shell. By soaking the nuts in water, the moisture content of the
kernel is raised, reducing the risk of it being scorched during roasting and making
it more flexible so it is less likely to crack. The CNSL is released when the
nuts are roasted. Its value makes collection in sufficient quantities economically
advantageous. However, for very small-scale processors, this stage is unlikely
to take place due to the high cost of the special roasting equipment required
for the CNSL collection. If the nuts are being manually shelled, gloves need to
be used or alternatively, the nuts should be tumbled in sawdust or ashes to absorb
the liquid coating which has a harmful affect on the skin.
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shell can be cracked either manually, using a hammer, or mechanically. Manually
operated blade openers are relatively in expensive; however the more successful
mechanical methods depend on the nuts having passed through the 'hot oil' CNSL
extraction operation. Care must be taken not to break or split the kernel at this
or subsequent stages as whole kernels are more valuable than broken ones. Once
the kernel is removed from the shell, it is dried, the testa is peeled off and
the kernel is graded. Figure 3 gives an overview of cashew nut processing and
the various choices in methods.
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raw nuts carry foreign matter, consisting of sand, stones, dried apple etc. The
presence of foreign matter in the roasting operation can be avoided by cleaning
the nuts. The raw nuts can be sieved by hand using a ¾ inch mesh sieve.
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next stage is to soak the nuts in water to avoid scorching them during the roasting
operation. This can be done by placing the nuts in a 40-45 gallon drum or vat
and filling it with water until all the nuts are covered. After being left to
stand for about ten minutes, the water should be drained off via a plug near the
base of the drum. The nuts should then be left for periods of not less than four
hours in order to allow the water left on the surface of the nuts to be absorbed.
The process of covering the nuts with water, draining and standing should be repeated
with the same nuts about three times until a moisture content of 9% is reached.
Where
the production output runs from 2-10 tons of nuts per day, a simple cleaning and
conditioning arrangement can be used. Two people open the sacks of harvested nuts
on a stand and clean the raw nuts as they are moved along a flat sieve, to two
vats which are used for storage until the soaking process begins. Two vats are
useful because one can be emptied while the other is being filled.
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