Ever since we discovered them, we have been enjoying (and eating far too many of) the highly addictive Thai Lime & Chili Cashews from Trader Joe’s. These things should carry a warning label: “CAUTION: MAY BE HABIT FORMING.”
Anyway, while we eating them, we were asked if we knew why you can’t get cashews in the shell. We had no idea. Actually, we’d never thought about it. But, come to think of it, you can get almonds, walnuts, pistachios, brazil nuts, hazelnuts, peanuts, chestnuts, pine nuts, pecans, and even macadamia nuts in a shell, but not cashews.
Why? It turns out that the cashew shell is toxic. However, that raised the question of what a cashew looks like in its shell. Again, we had no idea. When we found out, we knew more people should see it. Weird looking, isn’t it? And caustic, too!
Cashews, like many of the culinary nuts listed above, are not true nuts in the botanical sense. True nuts develop a hard wall around the seed (e.g. hazelnuts). Cashews instead have a lining around the seed that is filled with a nasty fluid.
Cashews are in the same family (Anacardiaceae) as mangoes, pistachios, sumac, and poison-ivy. Many plants in this family produce Urushiol, an oil that can cause a nasty, painful rash. (Our friend Dan had not been told about this when he came across them in
Thailand Brazil, and burned his mouth on a fresh cashew. Ouch. He has some pictures of the local “caju” fruit here.) The cashew stores this icky stuff in the lining around the seed, which makes cashews very difficult to process. They are usually roasted to release the fluid, which is collected for other uses, such as varnish. After that, the hardened lining must be removed by hand.
That’s pretty weird, but it gets weirder. In the cashew, the ovary develops outside of the fruit, which really makes it a false fruit, since by definition fruits have seeds inside. The false fruit attached to the false nut looks like a pear with a little boxing glove hanging off the bottom. When ripe, the whole thing falls off the tree, and the bottom part is gathered for processing. The false fruit (called cashew fruit or cashew apple) is edible, but it is very perishable. It is often left to rot, but can be eaten raw, cooked, or used to make a liquor called feni. While the fruit and its juice are available in parts of the world where cashews grow, they are apparently too perishable to appear in stores in the US.
There is a lot more cool information about cashews out there. This article has plenty of additional details including uses, folk medicine, cultivation, and biotic factors, among other exciting topics. We recommend eating Thai Lime & Chili Cashews while furthering your knowledge.