The cashew tree, Anacardium occidentale, produces a complex fruit structure. This tropical evergreen tree, native to northeastern Brazil, is cultivated globally for its valuable edible seed, commonly known as the cashew nut. The nut develops at the end of a swollen, pear-shaped structure called the cashew apple, which is technically a pseudofruit. This peculiar arrangement—a kidney-shaped nut hanging below a fleshy, colorful apple—indicates that harvesting cashews is a multi-step process requiring specific timing and careful handling. Specialized steps are required to ensure the final product is safe for consumption.
The Ripening and Picking Process
Harvesting cashews begins with recognizing the distinct visual cues of maturity. The cashew apple swells to its full size, typically changing color to vibrant shades of yellow, orange, or red, depending on the variety. This color transformation signals that the apple’s sugars have developed and it has reached peak ripeness.
In tandem with the apple’s color change, the kidney-shaped nut attached beneath it also matures. The nut’s color shifts from a bright green to a grayish-brown, indicating the kernel inside is fully formed and the outer shell has hardened sufficiently. The cashew harvest typically occurs during the dry season.
The most common harvesting technique is to wait for the entire fruit assembly to drop naturally to the ground. This natural drop is the best assurance that both the apple and the nut have reached optimal maturity and quality. Once on the ground, workers manually collect the complete fruit and nut assemblies, sometimes daily in hotter climates to maintain quality. Manual collection minimizes damage and ensures that only fully ripened nuts are gathered.
Separating the Nut from the Apple
Once the complete cashew fruit assembly is collected, the next step is to separate the nut from the apple. The kidney-shaped nut must be twisted or carefully cut off from the fleshy cashew apple. This separation is often done manually, with care taken to avoid damaging the nut at its point of attachment.
The cashew apple can be ten to fifteen times the weight of the nut. Although the nut is the primary commercial product, the apple is a juicy, nutritious fruit rich in Vitamin C. The cashew apple can be eaten fresh, juiced, or used to make preserves, jams, and fermented beverages.
However, the apple is extremely perishable, with a shelf life of only about 24 to 36 hours before fermentation begins, making long-distance transport difficult. Because of this rapid perishability, commercial operations often focus on the nut. For the nut to be processed, it is dried in the sun for several days after separation to reduce its moisture content, a step that is essential for long-term storage and subsequent processing.
Safely Processing the Cashew Nut
The industrial processing required to make the nut edible and safe is complex. The raw cashew nut is enclosed in a double-walled shell that contains a dark reddish-brown liquid called Cashew Nut Shell Liquid (CNSL). This liquid is the source of the cashew’s danger.
CNSL is an oily substance containing phenolic compounds, primarily anacardic acid, which are chemically related to urushiol, the allergen found in poison ivy. Direct contact with CNSL causes severe skin irritation and allergic contact dermatitis. Consequently, the shell cannot be manually cracked open, and the raw kernel is inedible.
To neutralize the caustic liquid, the raw nuts must undergo intense heat treatment, typically high-heat roasting or steaming. Steaming involves exposing the nuts to high-pressure steam, which transfers the CNSL from the shell to the outside layer. Roasting subjects the nuts to high temperatures, often between 400 and 700 degrees Celsius, causing the liquid to char and escape from the shell.
This heating process converts the toxic anacardic acid into a less corrosive compound called cardanol. After the heat treatment and cooling, the nuts can be safely shelled, followed by a final drying and peeling of the thin, reddish skin surrounding the kernel. The resulting kernel is the familiar cashew nut, which, even when labeled “raw” in stores, has always been steamed or roasted to eliminate the dangerous shell liquid.