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Cashew nuts

Cashew nuts are the fruit of the cashew tree. The nuts hang from the end of a juicy peduncle, which is a pear-shaped, edible accessory fruit (‘false fruit’). It is the edible part inside the nut which is sold after shelling. Shelling is a complicated process which involves releasing the kernel from layers of shell and skin and, at the same time, recovering a highly corrosive product known as Adipostatin A (cardol).
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© Shutterstock / wichitpong katwit - Cashew apples

Cashew nuts, an amazing fruit

Cashew nuts are the fruit of the cashew tree, which is native to Brazil, but was brought to Africa and India by the Portuguese in the 16th century. Cashew trees can grow up to 10 metres tall. Cashew nuts are kidney-shaped and are attached to the bottom of ‘false fruit’ which grows from the flower stalks. These are called ‘cashew apples’, even though they look more like pears. Each ‘apple’ produces just one nut. Cashew nuts are 3 cm long and composed of a kernel covered by a thin skin and two shells. The inner shell is very hard and difficult to crack. Between the two shells is a toxic and highly caustic oily substance. If you try to remove the kernel with your fingers, this substance burns your skin and causes blisters.

The complicated extraction of the cashew nut kernel

When cashew nuts are ripe, they fall from the tree onto the ground where they are gathered up and separated from the ’apples’. Once dried, they are cleaned and stored in a humid environment for a few hours. Then they are roasted. This step enables the corrosive oily product between the two shells, which is mainly composed of Adipostatin A (cardol) and anacardic acid, to be released and recovered. The nuts are then sprayed with water, cooled down and dried, after which they are ready for shelling. Even though a machine has been invented in an attempt to automate the process, this step is still mainly carried out manually today. It involves tapping on the shell in a specific place to make a crack and then carefully widening the crack to extract the kernel. There is a thin skin around the kernel which must also be removed. Then, once the shells and skin have been removed, the kernels are roasted and finally ready to eat.

By-products of the fruit of the cashew tree

Only shelled cashew nut kernels are sold. As they turn rancid quickly, the kernels need to be stored preferably in vacuum-packed bags in the refrigerator. They are used whole, chopped, roasted, salted or unsalted. They are eaten whole, mainly as a snack. In the countries where they are produced, they are also used as cooking ingredients.

Cashew apples’ are eaten raw or cooked and made into juice and syrup. They can also ferment and be made into wine. In Brazil, the cashew tree’s native country, the apples are considered a delicacy and are preferred over walnuts.

Adipostatin A, or cardol, is collected and used to make varnish, resin, waterproofing products, ink and insecticides.