: is the liquid inside caled water or milk?
once open do i need to refrigerate it?
There is only one coconut, produced by the coconut palm tree, which may come in green or red/orange colours. The difference in green or brown is simply differing stages of maturation.
Green or young coconuts commonly have their tops sliced off, add a straw and presto you have a ready-made refreshing tropical drink! That is coconut water, which is very different from the coconut milk used in cooking. The meat is tender and translucent, which you can scrape out to eat after your drink or add it to fruit salads & canned mixed fruits for a tropical twist.
Brown or mature coconuts are commonly sold with the already brown dried husk removed. The meat has become more firm and opaque white. I understand that some people produce coconut milk by mixing the meat with the coconut water eg. Hawaiians. In South East Asia, the brown shell with just a thin layer of meat left is ground up. The fresh ground coconut is placed in a muslin bag with 1 cup of water added, the bag is then squeezed to produce thick coconut milk (equivalent to canned coconut cream); this is used in SE Asian desserts & added at the end of cooking curries for extra creaminess & coconut flavour.
After the first squeezing, about 4 cups of water are added for the second squeezing to produce a thinner coconut milk that is more liquid. This can be added during the curry cooking process, for desserts, making coconut rice etc. Note that if you let coconut milk boil, it tends to separate and the resultant curry has a higher chance of turning rancid. And yes, you need to refrigerate coconut milk as it spoils fast.
If both fresh mature coconuts and canned coconut milk (the thinned one) are not available, the next best thing is canned coconut cream (diluted with water to required consistency). There is also coconut powder (follow the package's instructions to reconstitute), but I find when cooking curries, the final gravy is obviously different from one prepared using fresh coconut milk. The very last resort is to add water to dessicated coconut to squeeze for coconut milk, but the result tends to be a bit oily.
Note that coconut is high in saturated fats and hence coconut milk & oil should be consumed infrequently & in moderation. Otherwise, the risk of heart diseases and obesity is very real.