From trees, of course! Cashew nuts are under a family called tree nuts and they grow mainly in India, Vietnam, Brazil and Africa. The temperature for growing them is about 10 to 40C, so 25C is perfect for them. They are rather tough and drought resistant so they grow pretty well in any conditions. These are the cashew seeds growing on a tree:
Take a look below at how the whole cashew tree looks like:
From the picture, you will see fruits on it. Cashew nut is only a part of the fruit. Cashew apple is actually the real term and you can actually eat them! It is high in Vitamin C, juicy, refreshing but with a tinge of acidity. Not all apples are red, some are orange or yellow like the picture below.
Some people actually grow them for the cashew apples and not the nuts. I think it looks pretty cute like a mushroom with a grumpy face! In Goa, the cashew apple juice is even fermented and distilled to produce alcohol.
It takes 3 to 5 years to grow a tree from unshelled seeds. A grafted plant will be faster and time will shorten to just 18 months. To remove the nuts from the fruits is actually very dangerous because the shell of the nuts have a horrible, corrosive liquid that can burn you similar to poison ivy. There are 3 ways to get around this:
1) By freezing - The shells can be separated from the nut before it thaws. Gloves are still needed but the danger is decreased. Not many are using this method.
2) By roasting - Heat the oil to 210C and cook them for 2 minutes. The corrosive liquid will drain away so you will need some equipment with holes for them to flow. In modern technology, soaking of the nuts are done before roasted to prevent them from burning.
3) By steaming - This is more advanced technology where a steam cooker makes the shell soft so it is easily removed. Workers still have to oil their hands to limit exposure to the corrosive liquid in the fruit. The shell is still removed by hands so extracting a cashew nut is still pretty labour intensive. After which, you can get to eat the cashew nuts!
From this production, they can extract cashew oil for cooking or Cashew nut shell liquid (CNSH) as a raw material in chemical applications. The shells can also be used as biomass fuel. Growing a cashew tree is indeed very useful in many ways!
One more fun fact is that cashew trees grow flowers and produce fruits in the winter and not during summer! This is why only tropical countries can grow them. The nutritional value is also high with the rich amount of phosphorus, manganese, zinc and iron. After all that you have learnt, aren't you keen to taste some nice, fragrant cashew nuts?