While this wasn't actually done in Thailand, I believe the methodology is much the same....
A few years ago my daughter needed to do a "science" project. After a bit of discussion we decided we'd demonstrate how to make coconut oil the old fashioned way.
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First you need to gather coconuts. We had about 100 trees, so this wasn't too tough. The oil content will be higher if you pick nuts that feel from the tree when fully ripe, but which haven't sat around long enough to sprout.
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Next step is to husk the nuts. Coconuts are tough, but with the right tool and some practice you can do it pretty quickly. This happens to be an iron bar welded to an old wheel rim. We've also used a pick with one end buried in the ground or even a sharpened piece of ironwood buried in the ground.
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I think we husked about a dozen nuts.
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The next step is to remove the meat from the husk. We're using a notched, curved piece of steel that's connected to a short stool. In the old days they would have used a piece of clam or oyster shell instead of the steel.