Traditionally, much of the raw Eastern African production has been shipped to India for processing and re-exported as kernels. Manual processing, such as that practised in India, tends to give higher yields of whole kernels than the mechanised methods in use in Africa and Brazil (Errington and Coulter, 1989). This practice decreased toward the end of the 1970s and early 1980s when production in the exporting countries declined.
Most of cashews produced in Guinea are exported to India for processing. There is, however, a cashew processing centre in Quinhamel at which some local processing takes place. Raw cashew nuts are boiled in a large cauldron for 25 minutes, then sun-dried for 48 hours. This makes it easier to separate the nut from the shell. Shells are removed from individual cashews using a foot-powered shelling machine.
The kernels are spread over special cooling screens and dried for seven hours at 77?C. The thin testa covering the kernel is subsequently manually removed by workers sitting at a row of tables. The cleaned kernels are then graded in accordance with their size and wholeness. The smallest pieces are collected for use in pastries and confectionery. Once separated and classified according to international standards, the cashews are roasted and packed for shipping.
All parts of the cashew are used during processing. The discarded shell is burned to heat the cauldron in which the raw nuts are boiled. The skins can also be burned or mixed with grains for livestock feed and the ovens can be fired from the pruned branches obtained from a well maintained orchard.
Home based cashew processing has very low energy requirements, in that fuel is required only for cooking and drying. Workers shell and clean the cashews during daylight hours. The cashew shelling machines which were originally imported from Brazil are manually operated. These machines are now made locally. Cashew processing is thus regarded as a low-input activity that is suitable for the small scale or domestic level. Sale of the processed nuts provides year round employment opportunities, unlike the sale of raw nuts for processing abroad which only provides a few months of employment a year.
Those African countries which experienced a decline in their cashew production capacities may now be in a position to revive the industry, particularly at the small-scale. Following the Indian example of small-scale manual processing, rather than continuing with the old concept of large plants that are unable to operate efficiently, will be the most appropriate way forward and will provide opportunities for small-scale processors.
India is the main cashew processing country in Asia. The highly skilled workforce and low labour costs in India, allowed it to have a virtual monopoly on the manual processing of cashew for many years. Raw cashew nuts were traditionally shipped from Africa to India for processing, because of the reputation of the high quality of processing in India.
Cashew production and processing provides employment to over 500 000 people in farms and factories. Over 95 percent of these workers are women from the poorer sectors of society. In Mozambique, cashew production and processing used to be the fourth most lucrative business, providing incomes for millions of peasant growers and over 10 000 processors.
The traditional practice in the south Arcot region of India was to spread the nuts out on flat rocks in the sun, so as to allow them to dry until the shell became brittle. The kernel could then be removed from the shell by striking the nut with a wooden batten to split the shell along the natural line of cleavage. The cashew kernel was removed from the shell without becoming contaminated by the CNSL. Use of this method was made possible by the suitability of humidity and climate condition in that particular region of India. Shells are further processed to obtain the CNSL.
An alternative method of removing the kernel from the shell is to subject the nuts to very low temperatures, thus causing the shell to become brittle. Following this, the nuts are mechanically cut along the natural line of cleavage and the kernels removed. The shells are then further treated to remove the CNSL. This method of kernel removal has been commercially adopted.
Open pan roasting
Open pan roasting is used by traditional cashew processors in India. This roasting technique is very simple with minimal equipment requirements. It however requires skill and judgement in order to prevent the nuts from burning.
The roasting pan is an open circular mild steel dish, measuring 600 to 675 mm (2 to 2.5 feet) in diameter, supported over an open fire. Between 1 and 1.5 kg of raw nuts are placed on to the heated pan at a time. The nuts are heated on the pan, with constant stirring, in order to prevent burning (Figure 6). As the nuts heat up, the CNSL is exuded onto the pan and eventually ignites, producing clouds of thick black smoke. After heating and burning for about two minutes (judged by experience) the pan is dowsed in water and the nuts are thrown off and allowed to cool, during which the shells become brittle and can be readily removed from the nut.
Figure 6: Pan roasting
Cleaned raw nuts are spread in a single layer on the ground under bright sunlight for six to seven hours a day, over a two to three day period, in order to attain the correct stage of dryness. Partially dried nuts are covered with polythene overnight. A trained processor can determine the correct stage of dryness by shaking together a few dried nuts in the palm of his hands, to give the correct rattling noise.
Processors sit on the ground and shell the nuts by beating with a mallet two or three times on the same spot, until the shell cracks. A hard stone is buried in the ground to serve as a stable platform on which to rest the nut for shell breaking. After the shell is broken the kernel is extracted using a small metal tool resembling a penknife. This method is hazardous to the processor since the CNSL oozes out of the shell onto the hands. The processor wears rubber gloves and uses firewood ash sprinkled onto the floor to neutralise the caustic liquid. The firewood ash also helps to grip the nut. In addition to the danger posed by the CNSL, this method of kernel extraction is very labour intensive and uncomfortable for the women involved in these activities (ITDG Sri Lanka).
Pre-heating and peeling
After extracting the kernel from the shell, the testa, which is a thin reddish coloured skin covering the kernel, must be removed. Removal of the testa is facilitated by drying through slight heating. Care must be taken not to overheat the kernels as they become scorched and discoloured. Traditionally the kernels are heated on either a metal plate or open pan over an open fire. The kernels are tossed over the heat to avoid roasting and burning. An alternative and preferable method is to use a mechanical drier maintained at 55 to 60?C. The kernels are loaded into the drier and dried for three to four hours until the nuts give the appropriate sound when rattled together. Although investment in a mechanical drier is costly, mechanical drying gives a higher quality cashew kernel.
The testa is scraped off the kernel using a small blunt knife. Any burnt or discoloured spots are also scraped off the kernel with the knife. Care must be taken when peeling not to scratch the surface of the kernel as this can trigger off enzymatic browning and reduce the quality of the kernel.
The peeled kernels are divided into wholes, splits and broken pieces. They are stored in bulk in cardboard cartons or polythene bags.
Kernels are dried to a final moisture content of five per cent, using either a mechanical drier or oven. It is important to ensure that the drying temperature is not too high as this would cause roasting and discoloration rather than just drying of the kernels. Trained processors examine the kernels for the correct level of dryness by observing the colour and texture and shaking a few nuts together to hear the correct sound.
The dried kernels are further graded into sizes 180W, 240W and 320W according to the size of the nut. This process is carried out by experienced graders.
The type of packaging used is largely dependent on the target market. For the local market, kernels are packed in bulk and sealed in polythene bags. For the export market they are packed and flushed with nitrogen. Regardless of the target market, cashews must be packed in airtight containers so as to avoid the absorption of moisture from the air. They must be stored away from sunlight in order to prevent oxidative rancidity.
In the manual shelling process, the nuts are placed on a flat stone and cracked with a wooden mallet. The sheller requires a few basic pieces of equipment, namely cans for shelled kernels and shelled pieces, a shelling mallet, a striking point and a supply of wood ash to dust both the cashews and the fingers of the sheller. The working area should be kept clean to prevent the ash and spilled CNSL from contaminating the extracted kernels. This is quite easily achieved by organizing the work area and following an accepted routine.
Although this is a laborious routine, efficiency can be improved if attention is paid to ergonomic details, such as the positioning of the pile of nuts in relation to the striking point. The nuts for shelling and the tin for receiving must be correctly positioned so as to avoid wasting effort in reaching from one to the other. The raw and cleaned nuts must also be separated in order to avoid contamination of the extracted kernels. If the sheller is right-handed, the pile of nuts for shelling should be placed on the left hand side. The nut is picked up in the left hand and struck with the mallet on the right hand. The kernel is removed and deposited in the receiving can in the centre or on the right hand side. The shell pieces are brushed aside into a pile. The hands and striking point have to be regularly coated in wood ash to keep the kernels clean.
Shelling is a technique that can be relatively easily learnt. Strength is not required for breakage of the shell. Correct positioning of the nut and the ability to hit the nut in the correct position, so as to allow its breakage is most important. If the nuts have been properly roasted and are correctly positioned on the striking platform, they will easily break down the natural line of cleavage when struck at the broad end. The convex side of the nut should be placed in contact with the striking platform, with the plane of cleavage at right angles to the surface of the striking post. Occasionally, a nut will require more than one strike in order to open the shell, but this technique comes with practice. 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 5 kg of kernels. At an extraction rate of 24 percent, this quantity corresponds to about 21 kg of raw nuts per day or about 7 tonnes per year. Experienced shellers in India can produce around half as much again, with a quality of 90 percent whole kernels. A good sheller will produce a high percentage of clean, unbroken kernels, whereas a poor sheller will produce a larger quantitiy of dirty broken kernels (FAO, 1969).
For optimum shelling efficiency, the raw roasted nuts should be delivered close to the sheller, such that he does not have to keep moving to fetch them. The nuts should be delivered in small manageable quantities, since large piles of unshelled nuts act as a psychological barrier to the sheller and lower the quality of shelling.
The success of a cashew processing operation is largely dependent on the proportion of whole kernels produced in the shelling operation. Quality control and inspection are therefore critical in ensuring that shellers produce kernels of the highest quality. The critical period for quality control in the shelling operation is the start and the end of the day, but in particular the latter when the sheller may be rushing to complete the day’s work.
Several points must be to monitored:
Shellers need to be made aware of the quality of their work. They should be rewarded for high standards and penalized for work that is below par. At the end of the day the work place needs to be cleaned and tidied in preparation for next day’s work.
Processors may be required either by factory inspectors or health authorities to provide the shellers with gloves. Gloves are not, however, the most suitable form of protection against CNSL, in that they are cumbersome, become dirty and eventually perish from contact with CNSL. Wood ash is much more effective and has been successfully used for over half a century. The new processor may take a little while to get used to applying wood ash to his/her hands. Coconut oil is also used to protect the hands from CNSL.
Shelled kernels have a moisture content of over 6 percent which makes them susceptible to fungal attack. It is imperative that they be dried immediately after shelling.
Manual peeling is performed by gently rubbing with the fingers. Those parts still attached to the kernel are removed with the use of a bamboo knife. One person can peel about 10-12 kg of kernels per day.
It is important that the kernels are not cut or damaged during the peeling process. The use of knives increases the likelihood of the kernels becoming damaged, but it is also essential that all of the testa is removed. Gentle scraping of the testa with a blunt knife is the most effective way of removing it.
Peeled kernels can be separated into different grades with the use of a peeler. At the most basic level, the kernels are separated into white wholes, scorched wholes, white pieces, scorched pieces, browns and refuse. However, the more experienced graders are able to separate the kernel into a larger number of categories. It is preferable that grading is carried out at the time of peeling as this cuts down on handling of the brittle kernels. There is, however, the opportunity for further grading subsequent to peeling.