Anacardium occidentale, a small tree which bears a strange fruit. As the drawing shows, it has two parts: at the stem end a cashew ‘apple’, and projecting from the other end of the apple a smaller cashew ‘nut’. In fact the ‘nut’ is the true fruit, and it is only after the ‘nut’ has reached its full size that the ‘apple’ develops, as a fleshy expansion of what is called the receptacle of the nut. The degree of expansion is considerable; the apple may be over 10 cm (4") long.
When the apple is ripe, it and the nut fall to the ground together. Each then poses a problem. The apple keeps only for a very short time; it will spoil within a day at ordinary room temperature. The nut is in a hard double shell, between the two parts of which there is a caustic substance, as explained below, so the kernel is difficult to extract. In some countries the fruit is prized, for immediate consumption, or to be preserved in syrup or dried and candied; and the nuts are discarded. In other countries, the emphasis is on the nuts, and the fruits are left on the ground for animals to eat. Monkeys like them.
The native region of the cashew is thought to be NE Brazil. As long ago as the 16th century it was taken from there by the Portuguese to the E. Indies, whence cultivation spread to India. The Portuguese turned the Brazilian Tupi name acaju into caju, and names in most languages come from this. (In French acajou means ‘mahogany’, which has caused confusion. The two trees are unrelated.)
The cashew ‘apple’ is generally pear shaped; yellow or red; quite sour; and tending to be astringent and fibrous. However, a good fruit can be eaten raw, if sweetened. In Indonesia it is an ingredient in Rujak, a spicy fruit salad. However, it is usual to boil the fruit in slightly salted water for a few minutes to reduce the astringency, and it still needs sugar.
The nut is not easy to extract. The tissue between its two layers of hard shell contains strongly irritant substances, cardol and anacardic acid. This tissue has medical uses, including burning off warts, an indication of its great corrosive power. The usual way of treating the nut is to roast it whole, driving off the irritants and making the shell brittle enough to crack without crushing the contents.
The nuts, which have a delicate texture and a mild almond flavour, are highly esteemed. They are widely eaten as a snack or appetizer. The USA imports large quantities annually. In S. India and China they are often added, whole or ground, to savoury dishes.
The species Semecarpus anacardium, known as marking nut (because its outer shell yields a black, resinous liquid which can be mixed with lime to produce an indelible ink), is related to the cashew, and may be called oriental cashew. Both fruit (when cooked) and nut (once freed of toxins, e.g. by roasting) are edible, but neither is important as food.
Because its fruits resemble cashew ‘fruits’, the Malay rose apple (see rose-apple) is sometimes called French cashew or Otaheite cashew, but it is not related to the true cashew.