Anacardium occidentale L.
Cashew nut belongs to the Family Anacardiaceae together with Mango, Pistachio and Sumac. They have a type of fruit called a drupe (stone fruit). A drupe usually has an outer skin enclosing a fleshy middle that surrounds a single stone or shell. The stone contains the seed or kernel.
Cashew nuts are harvested from an evergreen medium sized tree up to 12m. The tree bears a strange fruit with two parts,: an expanded, pear shaped, red to yellow, ‘fruit’ at the stem end, called the cashew apple and at the apex, a single nut surrounded by a green leathery shell. The green nut at the apex is the true fruit. It contains a single bean shaped kernel which is commercially sold as cashew nut. The red or yellow ‘fruit’ at the stem end is a ‘false fruit’ commercially sold as cashew apple.
The main producers in order of importance are, Vietnam. Nigeria, India, Brazil, Indonesia, Ivory Coast, Philippines and Tanzania.
In East Africa and India, the main commercial product of the cashew tree is the nut. Africa produces more than 6 million tons of cashew apples per year and most are discarded at harvest, because the taste is not popular with the locals. They’re left on the ground for animals to eat, Monkeys love them. In South America and West Africa, the locals regard the cashew apple as a delicacy.
In Brazil the main commercial product is the red or yellow cashew apple, which is toxic, but is left to ripen and then processed to produce juice and many other products. (African Cashew Alliance)
The Cashew Nut
As mentioned above, the cashew nut is surrounded by a green leathery shell. The shell has an inner and outer wall. The two walls enclose sponge like interior infused with a thick toxic liquid called Cashew Nut Shell Liquid (CNSL) or Cashew Shell Oil. The composition of the liquid varies depending on how it is processed, but it’s strongly irritant to the skin.
Inside the toxic shell is a large curved, kidney shaped seed, nearly 3cm (1.2 inch) long which is the edible cashew nut. The seed is surrounded by a thin reddish brown seed coat (testa) which protects it from the toxic liquid. The kernel remaining after removal of testa is the cashew nut of commerce. The shell does not split open and therefore the cashew nut is very difficult to extract.
In order to extract the edible cashew nut, the green leathery shell has to undergo several stages of processing: (for detailed information on processing cashew)
Washing, Soaking and Drying
The green unshelled nuts are first washed to remove visible debris and then soaked in water to increase moisture content and avoid scorching during the next stage, roasting stage.
The soaked unshelled nuts are roasted in special roasting equipment. The oil is released and collected during roasting. The green leathery shell becomes brittle and easier to crack.
In India, shelling or cracking open of the shell is done manually. A nut is placed on a flat stone and cracked with a wooden mallet. Gloves are required because the residue from the toxic liquid is irritating to the skin. One worker can crack 5kg nuts in an 8 hour working day. The nuts can also be shelled using a semi-mechanized shelling system.
The shelled kernel is still covered with the seed coat (testa) and to facilitate removal of the testa, the kernel is dried. This reduces the moisture content from 6% to about 3%. The low moisture content also protects the kernel from pest and fungus attack at this vulnerable stage.
Removal of Seed Coat (Testa)
The seed coat or testa surrounding the kernel is removed manually by rubbing gently with fingers. One worker can peel 10-12kg kernels per 8 hour working day. The testa can also be removed using mechanized peeling methods like air blasting, suction, freezing or use of rubber rollers. Breakage is about 30%.
Grading and Packing
All grading is mainly done by hand or mechanical methods like power driven rotary. After grading, the moisture content is increased to 5% to make the nuts less fragile and reduce the risk of breakage, during transport. Packing is done in airtight containers.