The raw cashew nut processing sector has seen many technological interventions and breakthrough in the various processing stages. In earlier days, cashew processing was mainly manual as it was a work of the artisan whose art of processing was the key to realize maximum value (whole kernel- W grade) from the raw material. Careful roasting of RCN for easy shelling but without having burning or breaking impact on kernel, peeling off the testa (skin) without using sharp tool to avoid the scratch on the kernel and grading the kernel based on the colour and size are the key processing steps, where minimum mistake committed by the labour would gain higher return.
As the new Raw Cashew Nuts (RCN) contains lot of moisture, it needs to be dried to prevent quality loss of the nuts during warehousing. Drying and Calibration of RCN are the key processes done at this stage.
Drying of RCN: The freshly harvested RCN are dried by spreading it on the drying yard under the sun for the period of 1-3 days depending on the moisture content. The nut making rattling sound is the symbol that the raw nuts have been dried properly. However, it is necessary to monitor the drying process as over drying of RCN may cause scorched kernel which may lead to higher breakage during shelling. On the other hand, improper drying of RCN may again cause lower yield of wholes and de-colouring of kernel. Once RCN is received at the drying premises, the processors will check the moisture level by using moisture meter or some traditional method like poking pointed pin or nails and based on which days of drying is decided. Processors will avoid buying the RCN having more than 17-18% moisture as it may be immature. The RCN is spread on the drying yard throughout the day and kept in covered place during the night. Once the RCN is dried, it is calibrated, bagged, weighted and tagged with details before sending it to warehouse. In general, during the warehousing or storage, the RCN will be carrying 6-9% moisture level.
Calibration Process: It is also called size grading and pre-cleaning of the nuts. At this stage, the dried RCN is separated as per the nut size as well as impurities like dust, plant stalks, mud/stones etc. are removed. This practice is newly adopted by the processors as it is not only very useful in efficient utilization of shelling machine but enhancing the manual cutting/shelling rate also. In this process a calibrator/grader machine is used, the machine will have cylinder shaped sieves having whole of various dimensions/size and RCN passed through different wholes will be segregated and collected separately. The size of the whole varies from 17-18 mm to 23-24 mm which may yield 3-5 grades of RCN. However, as per the requirement of the customer the number of grads can vary. In general, in India, the processors would grade the RCN mainly into the three sizes, i.e. small, medium and big.
The raw cashew nut processing starts with cooking process. It helps in softening the outer cashew shell so that cutting or shelling becomes easy. There are three methods of cooking available in the cashew sectors, i.e. fire roasting, steam cooking and oil bath roasting.
Roasting is a traditional method and mostly abandoned now. In this technique raw cashew nuts (RCN) is roasted on the steel/iron tray directly heated by the firewood where the shell gets burnt.
Steam cooking is the most adopted method as of now. Here the raw nuts are cooked in a GI/steel vessel for 20-30 minutes using steam generated through the boiler (mini or large). Thereafter, it is cooled down at the room temperature for 18-24 hr. The steam cooking also has two different sub-methods, where the static or fixed cooking vessels or rotating drum steaming process is used. The static method is more common in India whereas the second one is popular in Vietnam where large quantity is cooked and operation is mechanized. The static steam cooker generally comes in sizes of 100 kg to 320 kg RCN per batch and bigger; in India minimum 320 kg capacity cookers are more popular. Based on the batch processing quantity, the number of cooking vessels is determined. The rotated steam cookers come in bigger size which may have capacity of carrying equivalent or more than 640 kg RCN per batch.
Some of the major improvements in our shelling are (1) Calibration of nuts into 3 or 4 size ranges prior to feeding into the Sheller; (2) feeding mechanism; (3) easy dissembling and maintenance of the machines/blades; (4) improvements to reduce oil contamination on the nut through automatic suction of shells; (5) scooping mechanism and (6) optimization of power consumption.
The de-shelled nuts will have high level of moisture which makes testa/skin to hold tightly to the kernel. This layer/skin needs to be loosened to ease the process of removing it in further steps. At this stage, shelled cashew is dried or roasted in the oven/hot house to reduce the moisture level so that the testa/skin can be peeled out easily. This is also a crucial stage where efficiency could determine the breakage of kernels.
Peeling is the last process from where cashew kernel appears in Ready-to-Eat form. At this stage, all the inedible parts/layers are removed from the kernel, the price enhancing value addition processes like grading, sorting, packaging etc., start from here. Peeling is the process by which the testa or outer skin attached to the cashew kernel is removed. The process looks simpler but a lot of care needs to be taken at this stage as around 60-75% of the processing cost is added up in the output recovered from here. Peeling is done through two processes, viz. manual and mechanical. In the manual process, the roasted/heat treated kernel is rubbed softly between the finger and palm of the hands to remove the testa. In the mechanical process, the humidified kernel is fed in the machine in which it passes through the rotating cylinder fitted with brush where the testa comes out. The testa is then separated by blowing air flow generated through the compressor.
As stated in the above process, the cashew kernel is treated through the humidification process to enhance the moisture content (4-5%) for peeling in the machine. The moisture level above 4% at the time of final packing is not preferred as it may cause fungi infestation; low moisture level below 2% is undesirable as it causes breakage of kernel during processing and shipment. It is desirable that the moisture level in the kernel at the time of packing should be 3%. Once the kernel is peeled, it again goes for drying/roasting process to maintain the standard level of moisture content (the moisture content in kernels need to be reduced to three percent as per the export standard norm), this process is called ‘Conditioning of the kernel’. Hot drying machine called ‘Dryer’ is used for this purpose. In general, machine peeled kernels are dried in the drier at 40-5 ° C for about four to five hours, however the duration varies based on the moisture content present in the kernel.
Cashew kernel prices are based on the various grades specified by the market. These grades are defined as per the size, colour and body texture etc. At present more than 24 grades of cashew kernel are traded in the markets. Women employees are largely used in grading/sorting/cleaning section. These skilled ladies have all expertise to correctly select the kernel for specific grades. Technology providers are still experimenting with the grading machine; to a certain extent they have succeeded also (grading the kernel for 5-8 grades based on the size, colour and texture) but still incomparable to the human grading methods.
At first step, splits, broken and whole are separated, this is mostly done using vibrator separator machine. Once the wholes are separated from others, they are graded using the grading machine. The grader could grade the kernel as per the specific size (mostly six to eight classifications). These nuts are then given for the colour based grading. For grading broken into various grades (as per the size), mechanized wire-mesh sieves are used.
Women labourers are employed for the grading job in almost all the cashew processing countries. These ladies will be given a certain quantity (in terms of weight) of cashew kernel to be graded and separated. Graded kernel is taken back at the end of the day. A supervisor/inspector will verify/inspect whether the graded nuts are as per the specification or not. To be more precise, wholes and splits kernel is distributed to the labour so that grading/sorting can be easier and convenient for them.
After grading and sorting the nuts/kernels into various grades, the last process is packaging. Before packaging a final Quality Checking (QC) process is done, in which the graded nuts/kernel is sent for dust removing and metal/hair detection process. Both, dust removal and metal detection processes are mechanical. In the dust removal process, kernel is passed through a closed chamber where pressurized air is used to blow out the dust and light particles. The metal detector process ensures that cashew is not contaminated with ferrous metals; the equipment will have the in-built online metal detection program.