There Is No Such Thing as a Raw Cashew

Go into almost any shop and you will find bags of cashews labelled raw. They look pale, plain and untouched, as if they had been picked off a tree that morning. They have not. Every one of them has already been through heat before it reached the bag, and the reason lies in the strange way the cashew grows and in what surrounds the nut inside its shell.

A cashew does not grow tucked inside a fruit the way a peach stone does. According to the horticulturist Julia Morton, in her book on tropical fruits published online by Purdue University, the true fruit of the cashew tree is the nut itself, hanging from the end of a swollen stalk called the cashew apple. The apple ripens into a yellow or red structure about 5 to 11 centimetres long, and the nut dangles from the bottom of it like an afterthought. What we eat as a cashew is the kidney-shaped kernel inside that nut.

The trouble is the shell. Morton describes a double shell with a caustic resin held in honeycomb-like cells, and the U.S. Centers for Disease Control and Prevention lists what is in that oil: a dozen distinct allergens, including cardol and anacardic acid, chemically related to the irritants of poison ivy, which belongs to the same plant family. Healthline, in an article reviewed by a registered dietitian, says raw cashews in their shell contain urushiol in the oil between the shell and the nut, and that it can cause a delayed skin rash similar to the one poison ivy causes. The CDC adds that the oil caused skin trouble among the workers who shelled the nuts, until modern processing equipment made it rarer.

So the nut has to be treated before anyone eats it. The CDC traced one outbreak of rashes, in 1982, to bags of cashews that had been incompletely processed, with pieces of shell still among the nuts. Healthline adds that even cashews labelled as raw in shops have been shelled and heat-treated, either through roasting or steaming, to remove urushiol residue. In other words, raw on a cashew bag does not mean untouched. It means it has not been roasted for flavour afterwards.

The cashew apple, meanwhile, rarely leaves the places where it grows. Morton explains why: fresh cashew apples are highly perishable and begin to spoil after a single day at room temperature. Where cashews are grown, the apple is picked up and chewed for its juice, preserved in syrup, made into jam and chutney, or turned into juice and wine, and in Goa it is distilled into a strong spirit called feni.

Which leaves most of the world in an odd position. We have spent our lives eating the small, hard, carefully cooked seed, and almost none of us have tasted the soft fruit it hangs from. The name, at least, remembers the whole plant: the Online Etymology Dictionary traces cashew to the Portuguese acajú, from acajuba, the name of the tree in the Tupi language of Brazil. The shop still calls the nuts raw. The tree knows better.