The objective of shelling is to produce clean, whole kernels free of cracks. In India, this operation has always been done manually. Other countries have difficulty in competing with the great skill and the low wages of the Indian workers. Therefore, India has enjoyed a virtual monopoly of cashew processing for a long time. Manual shelling is still relevant to the smallscale processor, although a close look at the mechanical option is advisable in all cases.
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In the manual shelling process, the nuts are placed on a flat stone and cracked with a wooden mallet. As mentioned above, because of the residue CNSL, wood ash for covering the shells or gloves are required. An average sheller can open one nut in about six seconds or ten nuts per minute. In an eight-hour working day, this amounts to about 4,800 nuts or about 5kg of kernels. At an extraction rate of 24%, this quantity corresponds with about 21kg of raw nuts per Cashew
nut processing Practical Action 5 day or about 7 tons per year. However, experienced shellers in India can produce around half as much again, with a quality of 90% whole kernels.
The most successful mechanical shellers work on nuts which have previously passed through the ‘hot oil’ process and is detailed under the paragraph ‘centrifugal shellers’. A semi-mechanised process that has been used predominantly in Brazil, uses a pair of knives, each shaped in the contour of half a nut. When the knives come together by means of a foot operated lever, they cut through the shell all around the nut, leaving the kernel untouched. Two people work at each table; the first cuts the nuts and the second person opens them and separates the kernel from the shell. Daily production is about 15kg of kernels per team. The first mechanised shelling system, Oltremare, is also based on two nut-shaped knives. The nuts are brought to the knives on a chain, each nut in the same position to fit between the knives. The nuts are pushed between the knives and cut.
The chain itself has to be fed manually. After coming together, the knives make a twisting movement, thus separating the shell halves. The disadvantages of this method are that nuts smaller than 18mm cannot be processed and output is reduced because not all the spaces on the chain can be filled which can count for as much as 10% of the production volume. The shelling machines of the Cashco system are also chain fed but the nuts are automatically placed in the right position. The shelling device has two knives that cut the sides of the nut and a pin that is wedged into the stalk end of the nut separates the shell halves. The advantage of this system is a fully mechanised operation with an output of about 75% whole kernel quality. Nuts smaller than 15mm cannot be processed. Centrifugal shellers use a system which is simple and enables a continuous flow. A rotary paddle projects the shells against the solid casing and the impact cracks open the shell without breaking the kernel.
All sizes of nuts can be processed by this method, however, it is necessary to grade the nuts into four or so group ranges because a different rotary speed is used for the various size groups. The percentage of whole kernels produced is around 75%. By preparing the shells with grooves and weakening the strength of them before the operation begins, the percentage can be increased. The speed of the rotor can thus be turned down and the risk of damaging the kernels is reduced.