Cashews are made edible through a careful processing method that removes their toxic outer shell, typically involving heat treatment followed by shelling.
Raw cashews as they come from the tree are not directly edible due to the presence of a toxic substance called urushiol, found in the shell layer surrounding the nut kernel. This is the same irritant found in poison ivy and poison oak. Therefore, a specific process is necessary to make them safe for consumption.
The Processing Steps
Making cashews edible involves several crucial steps to neutralize the urushiol and extract the kernel safely.
1. Softening the Shell
The process often begins by treating the cashews to soften their tough shell. This can be achieved through:
- Boiling: Heating the nuts in water.
- Roasting: Applying dry heat.
According to the reference, "The nuts are often boiled or roasted to soften the shell." This step is vital as it makes the subsequent shelling process much easier and safer.
2. Shelling the Nut
Once the shell is softened, the cashew kernel must be extracted. This is a delicate and dangerous step because the toxic urushiol is still present in the shell.
- Manual Shelling: Traditionally, this is done by expert personnel who are trained to handle the nuts cautiously.
- Mechanized Shelling: Modern methods utilize a mechanized press to split the shell open.
As highlighted in the reference, the "nuts must be handled cautiously throughout the shelling process since the shell is exceedingly tough and contains a poisonous chemical that can irritate the skin." Safety is paramount at this stage.
3. Drying and Peeling
After shelling, the raw cashew kernels still have a thin skin or testa. They are typically dried thoroughly and then this skin is removed.
4. Final Roasting
Finally, the cashews are usually roasted again or fried, often with oil and salt, to achieve the desirable texture and flavor that we associate with edible cashews. This final heat processing also helps ensure that any residual urushiol is neutralized.
Why Processing is Essential
The intricate process of boiling or roasting, careful manual or mechanized shelling, drying, peeling, and final roasting is necessary solely because of the hazardous nature of the cashew shell. Without these steps, consuming raw cashews would lead to painful skin irritation and other adverse reactions due to the urushiol content. What we buy as "raw cashews" in stores have already undergone this initial steam-processing or roasting to remove the toxins from the shell.
