The cashew apple contains a high concentration of tannins which are the same substances found in tea and wine. They give the apple a very distinct taste.
The true fruit of the cashew tree is a kidney or boxing-glove shaped drupe that grows at the end of the pseudofruit. The drupe develops first on the tree, and then the peduncle expands into the pseudofruit. Within the true fruit is a single seed, the cashew nut. Although a nut in the culinary sense, in the botanical sense the fruit of the cashew is a seed. The seed is surrounded by a double shell containing a dermatogenic phenolic resin, urushiol, a potent skin irritant toxin also found in the related poison ivy. Some people are allergic to cashew nuts, but cashews are a less frequent allergen than nuts or peanuts.
The green fruit contains urushiol oil, the same substance found in poison ivy and poison oak which irritate the skin. You have to be very careful when removing the nut and it is for this reason that I have never purchased a whole, fresh cashew for myself and experimented with it. In an older article from Purdue University Horticulture I read that in some countries at one point the nut was simply thrown out with the fruit due to this toxin and much more emphasis was placed on the apple.
Cashews are grown in other tropical places throughout the world such as Vietnam and India. However, unless you live very close to one of those places it is likely you will never see a whole cashew. The fruit is juicy, fragile and spoils very quickly so extended transport is not an option.
I have grown to love cashew juice which is made from the cashew apple. It has a sweet flavor with a richness that resembles that of the nut. The tannins leave that familiar drying feel in the mouth which they are known for. This is the reason my husband does not prefer it, but for me it gives the juice a unique appeal.