Cashew nuts can be harvested early, while they are still tender, more like a bean, but green nuts can be extremely bitter. Cashews have two shells. The outer shell is hard. The inner shell, called a testa, is more like a skin. The inner shell covers the nut itself, which occupies only a portion of the larger, outer shell. Both should be removed before the nut is consumed.
Watch for the cashew apple to turn a deep pink, red or yellow color (depending on the variety). Watch for the cashew nut's shell to turn a deep gray. The nut is kidney shaped, found hanging from the end of the fruit.
Harvest is possible in several ways. Harvest from the ground after the fruit drops. Collect the fruit when freshly fallen for best quality. Pick the fruit from the branches. Shake the branches, causing fruit to fall, or thrash the branches, separating the fruit from the branch.
Once the fruit is collected, pull the nut away from the apple. The fruit can be eaten or discarded. The nut can then be stored or processed.
Wear protective clothing, including eye protection, to process the nuts. Shelling raw cashew nuts can be dangerous because the shells contain cardol, a toxic fluid which is an irritant. The irritant in the shells should not be allowed to come into contact with the eyes or skin.
Cashews are a relative of poison ivy, oak and sumac; their cardol can cause a very painful skin rash. If the nuts are consumed with the liquid still present, it can cause blisters in your mouth.
Prepare the nuts to be eaten by removing the liquid cardol and both shells. The nuts can be opened by cracking the shell between a mallet and hard surface, but this leaves the nut exposed to the cardol. This is a low-tech method of processing and not recommended.
Dry the cashew nuts in the sun, and store them in insect-resistant bags for up to 11 months, or store them in air-tight containers for 8 months. These nuts can be shelled without roasting.
Steam roast, roast in an oil bath or drum roast the nuts. Cool using air or a water bath. Remove the shells, peel away the testa, allow the nuts to dry and then store or eat them.
Roast the nuts (in the shell) outdoors, over an open fire. The shallow roasting pan may have holes in the bottom to allow the cardol to drain away. Be aware that the fluid in combination with the flames may cause irritating fumes and hot, caustic liquid may spray out from the nuts or the pan.
Some large scale processors of cashews roast the nuts in small batches once they are outside of the shell. Others use an enclosed, perforated cylinder to roast the cashew while in the shell. This method drains away the cardol, which is collected and sold for industrial use.
The roasting time varies with the variety of cashew and other conditions. Once the nuts reach an ivory color, they are allowed to air cool, and during that time they turn the light brown we recognize. Salt the nuts while they are still warm.