The Blister Nut
I love cashews. Eat ’em daily. And, truthfully, I have never wondered why they are so much more expensive than other nuts. Nor have I ever wondered why you never see a cashew in its shell. But others have and it turns out the answers are related.
Botanically, the cashew fruit is related to poison ivy and the shell (though not the nut itself) contains a substance called cardol which is extremely caustic and will cause a nasty rash. This is why the cashew is also known as the blister nut. (Why god why does that not have an entry in Urban Dictionary?)
It is also why they cost so much since harvesting them is inherently dangerous and there is no good mechanical way of shelling them. Shucking is done by (presumably glove-wearing) manual laborers who have to deal both with the possibility of contact and the fact that the cashew fruit is just damn ugly, lewd even.
So you got two options if you really want to eat a cashew shell. The first is to say screw it, eat it, ulcerate your mouth and swell up. The second is to roast the hell out of the cashew. This boils off the poison, but be careful: apparently even the smoke can cause severe reactions.
But it isn’t all bad. Apparently the oil can be used as rocket lubricant. Oh, and I really enjoy saying blister nut. Blister nut. Blister nut. Try it, you’ll agree.
It is a damn good thing this little bit of trivia was not delivered to me earlier in the day. I’d have wasted even more time fascinated by it. (But thanks Juan!)