What do you think of this fact?
You can buy pistachios in the shell, peanuts too, walnuts obviously. But have you ever seen a cashew in its shell at the store? Probably not. And there’s a pretty good reason: the cashew shell contains a caustic oil.
An oil that blisters
According to Alimentarium, the Swiss food museum, the cashew has two shells. Between them sits a toxic, highly caustic oily substance that can blister your skin if you touch it directly. That’s why cashews get roasted after harvest, to release the oil. Then the shell is carefully cracked, still mostly by hand today, and finally the thin skin around the kernel is removed.
According to Scientific American, the shell contains urushiol, the same compound that gives you an itchy rash from poison ivy. The cashew belongs to the cashew family, Anacardiaceae, together with mango, poison ivy and, yes, pistachios. Roasting at high temperatures destroys the troublesome oil before the nut ever reaches you.
The nut that hangs outside
The second surprise is on the tree. The cashew doesn’t grow inside a fruit. It hangs off the bottom of one. This pear-shaped “cashew apple” is a false fruit, and each one carries exactly one nut. According to Alimentarium, cashew apples are eaten raw or cooked, turned into juice and syrup, or fermented into wine.
The cashew tree originally comes from Brazil. Portuguese traders brought it to Africa and India in the 16th century.
Mangos belong to the cashew family too and, according to Scientific American, carry urushiol in their skin.
A lot of work for a snack
If cashews ever seem pricey: every single one has been roasted, cracked and peeled, often by hand. Even the extracted oil gets used, according to Alimentarium for things like varnish, resin and inks.
The most harmless-looking nut in your trail mix has a surprisingly well-armed past.