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Six Main Steps in Raw Cashew Nut Processing
1. Drying of RCN:
After the raw cashew nuts are procured, they are dried to reduce their moisture content to a maximum of 9% by weight. This moisture content is ideal for warehousing and helps to prevent deterioration of the nuts during storage. Drying can be done on a clean concrete floor, on tarpaulins spread on a flat surface, or using drying machines that run on electricity1. Once the nuts are sufficiently dried, they are bagged in jute sacks for warehousing and later use throughout the year.
2. Pre-treatment of RCN:
Pre-treatment encompasses all the processes that take place before shelling, and includes three steps: calibration, warehousing, and heat treatment of the dried nuts.
Calibration of nuts: Calibration is the process of grouping nuts into various sizes according to their diameter. Common sizes are 18 mm, 20 mm, 22 mm, 24 mm, and more than 24 mm. The nuts are calibrated and then stored in jute sacks according to size. Calibration is particularly important for mechanized shelling machines, as it allows for accurate adjustment of cutting blades based on nut size.
Warehousing: This step involves storing the procured raw cashew nuts for processing throughout the year. Processors procure their raw cashew nuts during the cashew season, which typically lasts three to four months each year. Proper warehousing is essential to prevent damage to the nuts from pests and pathogenic organisms, and helps to maintain their quality throughout the year.
Heat treatment of RCN: Heat treatment is necessary to ease the separation of the kernel from the shell. There are three methods of heat treatment: steaming, drum roasting, and oil bath roasting. Steaming is the most prevalent method for heat treatment. It is done in a boiler to make the shells brittle and easy to cut. Once the steaming process is complete, the nuts are spread evenly on a clean surface to cool completely, a process known as air drying. Steaming also concentrates the CNSL into a jelly-like fluid, which reduces its corrosive effect on workers’ hands during manual shelling.
3. De-shelling:
De-shelling is the process of separating the kernels from the raw cashew nut shells. The goal is to obtain the highest possible percentage of whole kernels and prepare them for peeling. De-shelling is a crucial step in the process, as precision and accuracy are vital to minimize kernel breakage.
Removal of the shell: The shell is removed by either cracking or cutting the raw cashew nuts to extract the kernels. This can be achieved using manually operated machines or fully mechanized shelling machines. Regardless of the method, some manual separation of the kernel and shell is typically required.
Oven drying and humidification: Also called thermal shock, oven drying and humidification facilitate the removal of the testa without damaging the kernels. The kernels undergo a process of heating (drying), humidification, and reheating to complete the thermal shock process. The alternating contraction and expansion of the testa during this process weakens the bond between the testa and the kernel. Oven drying is typically done in specialized ovens called Borma, and humidification takes place in a humidifier or thermal shock chamber.
4. Peeling:
Peeling involves removing the testa from the kernel. Many factories use a combination of peeling machines and manual peeling. Peeling machines use friction and air pressure to remove the testa, but they may not completely remove it from all kernels. Manual peeling, typically using small knives, is often necessary to ensure complete testa removal.
5. Grading:
Grading entails classifying the kernels based on their color, shape, and size. Grading can be performed manually using skilled labor, or with cashew grading machines. Cashew kernels are graded into white (W), scorched (S), and dessert (D) categories based on color. They are further classified as either whole (W) or broken kernels based on shape. Broken kernels are further categorized by shape into splits (S), butts (B), pieces (P), and baby bits (BB).
6. Packaging the kernels for storage and shipment:
After grading, the kernels are stored in containers according to their grade and labeled for identification11. Before packaging, the kernels are conditioned to maintain a moisture content of 3.5%–4%, which is ideal for packaging. This moisture level prevents both breakage and clumping of the kernels11. Fumigation is also performed before final packaging to protect the kernels from pests and pathogenic organisms11. The most preferred method for packaging cashew kernels is vacuum packing, which involves back flushing the kernels with a mixture of carbon dioxide and nitrogen to extend their shelf life.
