I make young coconut kefir regularly — however I use water (sugar) kefir grains, not milk grains. I think it’s tricky to transition the milk grains, but the water grains do OK, especially if you alternate the grains occasionally to a regular water kefir recipe that will give the grains the nutrition they need to keep growing.
I ferment just the water, so as not to have issues with coconut meat getting mixed up with the grains (been there, done that!). I ferment the meat separately, by blending it with just enough of the coconut kefir to make a nice creamy consistency. Then it ferments very quickly – no grains necessary (don’t overfill this jar for sure — been there, done that too!).
Now I add fresh ginger juice to the coconut water and my water kefir recipes too. Not only does it taste great (a bit like ginger ale or even ginger beer), and the ginger certainly adds health benefits, but the grains seem to like this as well. I think it acts as a natural retardant for some of the less beneficial strains (sometimes I found my coconut kefir becoming a little too yeasty if I left it unrefrigerated for too long).
Oh, also, it’s easy to find the soft-spot on the bottom of the coconut if you take a good serrated knife and slice off a couple of thin layers of the shell off the bottom. You’ll be able to see one or more small rings where the spot is, and the point of the knife can easily penetrate it to make a large enough opening to drain the water.