Cashews Grow on Apples

That familiar kidney-shaped nut is only part of a much stranger botanical picture. The cashew grows from the bottom of a fleshy, pear-shaped stem called a cashew apple. Botanically, the cashew apple is a "pseudofruit" or "accessory fruit (Review)," while the actual fruit is the hard-shelled drupe containing the cashew seed that dangles beneath it. In its native Brazil and other tropical regions where it's cultivated, the sweet and astringent cashew apple is highly perishable but is often eaten fresh, juiced, or fermented into liquor.

The primary reason we never see cashews sold in their shells lies within that protective casing. The shell is ingeniously defended by a toxic (Review), caustic resin containing anacardic acid, a compound closely related to urushiol, the irritant found in poison ivy and poison oak. Handling the raw shells can cause severe contact dermatitis. To render them safe, cashews must undergo a careful roasting or steaming process that neutralizes the toxic oils before they are painstakingly shelled and prepared for sale. This means that even "raw" cashews found in stores have been heat-treated to ensure they are safe to eat.