The cashew tree originated in Brazil and is related to the pistachio and the mango. It now grows mainly in Africa and India, where it was introduced by the Portuguese during the 16th century. The nut of the cashew tree did not become commercially valuable until the beginning of the 20th century. The leading producers of cashews are India, Brazil, East and West Africa and Vietnam. India, which produces 90% of the world's cashews, exports more than any other country.
The cashew tree usually grows to be 32 to 40 feet high and can produce nuts for 3 to 20 years, and occasionally for as long as 45 years. Cashew nuts hang from fleshy fruitlike peduncles that are sometimes referred to as "apples" but actually look more like pears. Cashew apples, each of which produces a single nut, are soft and contain an abundance of milky juice, which can stain clothing. Either yellow or bright red in colour, they are 2 to 4 inches long and 1? to 2 inches wide. Their fine yellow flesh is refreshing and is very rich in vitamin C; in fact, it contains much more vitamin C than oranges.
Cashew nuts measure just over 1 inch in diameter and are enclosed in two shells. The smooth, thin exterior shell is initially olive green but becomes brownish red as the fruit develops. The interior shell is very hard and can be difficult to break open. There is a very caustic resinous oil known as "cashew balm" between the two shells; it can burn and blister your fingers or lips if you try to remove the nuts manually or by biting into them. This corrosive liquid is used primarily to make varnishes and resins that protect wood against termites, as well as waterproofing products, ink, and insecticides. The wood of the cashew tree is very hard and precious, and its bark contains a yellowish gum that is used like gum arabic.
Cashew "apples" are gathered by hand after they ripen and fall to the ground. The nuts are removed from the apples and then dried for 2 days in the sun. They are always shelled and treated before being sold. Treating cashew nuts is quite an elaborate process. After being removed from the fleshy portion of the fruit, the nuts are cleaned, then stored in a humid environment for 12 hours, until they become fragile. These fragile nuts are then roasted in a rotating cylinder, which removes and recovers the corrosive cashew balm. After this initial roasting, the nuts are sprayed with water, then chilled and dried. At this point, they are ready to be shelled (which is often done mechanically) and peeled. Finally, they are roasted again, in two stages: halfway through this final roasting, they are sprayed with a mixture of gum arabic, salt, and water.