Cashews are a popular snack, known for their creamy texture and distinctive flavor. Most consumers only encounter cashews in their shelled, ready-to-eat form. This often leads to curiosity about their natural appearance and why they are never sold in their original shells.
The Cashew Plant and Its Unique Fruit
Cashews originate from the cashew tree (Anacardium occidentale), an evergreen tree native to South America. It is now cultivated in tropical climates worldwide, including India, Vietnam, and parts of Africa. The tree produces a “cashew apple,” a fleshy, pear-shaped or bell-shaped accessory fruit, not a true fruit. This vibrant yellow or red “apple” can grow to about 5–11 cm (2–4¼ inches) long and is juicy and sweet, though it has a short shelf life.
The true cashew nut, which is botanically a seed, develops outside and at the bottom of this cashew apple. It appears as a small, kidney-shaped or boxing-glove-shaped drupe, hanging like an appendage beneath the colorful cashew apple. This unusual growth pattern, where the seed develops externally, distinguishes cashews from most other fruits and nuts. Each cashew apple typically bears only one cashew nut at its base.
Unveiling the Cashew Nut’s True Shell
The shell encasing the edible cashew kernel has a complex, multi-layered structure. This hard, kidney-shaped casing is typically grayish-brown and measures around 2.5 centimeters (1 inch) in length. It is not a simple, single layer like many other nut shells.
The cashew nutshell consists of an outer layer, the epicarp, and an inner, harder layer called the endocarp. Between these two layers lies a spongy, honeycomb-like mesocarp, which contains a caustic, reddish-brown oily substance known as cashew nutshell liquid (CNSL). This liquid is a potent irritant. Both the endocarp and a thin, papery coat called the testa work to protect the kernel from direct contact with the CNSL.
Why Cashews Are Always Sold Shelled
Consumers never encounter cashews in their natural shells because the cashew nutshell liquid (CNSL) is harmful. This oily resin contains powerful irritants, primarily anacardic acid, cardanol, and cardol, which are chemically related to urushiol, the substance found in poison ivy and poison sumac. Direct contact with CNSL can cause severe skin irritation, blistering, and allergic reactions. Ingesting raw, unprocessed cashews with this toxic oil can also lead to adverse health effects.
To make cashews safe for consumption, they must undergo a specialized and rigorous processing procedure. This involves heat treatment, such as roasting or steaming, which helps to destroy or neutralize the toxic compounds within the shell. After this, the shells are carefully cracked open, often by hand or machine, to extract the edible kernel, ensuring minimal contact with the residual irritants. This complex and labor-intensive process explains why cashews are exclusively sold shelled and ready to eat, safeguarding consumers from the shell’s harmful properties.