Cashews, with their distinct kidney shape and buttery flavor, are a popular snack and culinary ingredient. Many consumers rarely encounter cashews in their natural, unprocessed state. This often sparks curiosity about their origins and why, unlike most other nuts, cashews are consistently sold without their shells. The journey from tree to edible kernel involves unique botanical characteristics and careful processing.
The Cashew Tree
The cashew originates from the Anacardium occidentale tree, an evergreen species belonging to the Anacardiaceae family, which also includes mango and pistachio. Native to tropical South America, particularly northeastern Brazil, the cashew tree was widely disseminated across tropical regions by Portuguese explorers in the 16th century. Today, it thrives in warm, humid climates, with significant cultivation in countries like India, Vietnam, and various parts of Africa.
This versatile tree can grow quite tall, reaching up to 14 meters, though dwarf cultivars, typically around 6 meters, are often preferred for their earlier maturity and higher yields. The cashew tree is characterized by its broad, leathery leaves and a spreading canopy. It produces both a fleshy, edible structure commonly known as the cashew apple and the true cashew “nut,” which is botanically a seed.
The Cashew Fruit and Its Unique “Nut”
The development of the cashew is unusual, distinguishing it from most other fruits and nuts. What is widely recognized as the “cashew apple” is actually an accessory fruit, or pseudofruit, that forms first. This pear-shaped, colorful structure, typically yellow or red, develops from the flower’s stem and receptacle.
The actual cashew “nut,” which is botanically a kidney-shaped seed, grows externally at the bottom of this cashew apple. This seed is encased within a tough, double-layered shell. Between these layers lies a caustic, oily resin known as cashew nut shell liquid (CNSL), composed primarily of anacardic acid, cardol, and cardanol. The part of the cashew that is consumed is the edible kernel found inside this protective shell.
Why Cashews Are Never Sold in Their Shells
The primary reason cashews are never sold in their shells stems from the presence of cashew nut shell liquid (CNSL), a potent irritant found within the raw shell. This liquid contains compounds chemically related to urushiol, the oily substance responsible for the itchy rash associated with poison ivy. Direct contact with raw cashew shells can cause an allergic reaction, leading to skin irritation, blistering, and inflammation.
To render cashews safe for consumption, they must undergo careful processing, which involves several steps. The raw nuts are typically heat-treated, often through roasting or steaming, which helps to neutralize the toxic compounds in the shell and makes it brittle. After this initial treatment, the shells are meticulously removed, either manually or using specialized machinery.
Even cashews labeled “raw” in stores have undergone this essential heat-treatment and shelling process to ensure they are free from the harmful irritants. This labor-intensive processing contributes to why cashews are generally more expensive than other nuts.