From Fresh Coconut

The flesh of one nut will give about half a litre (one pint) of santen. Grate all the flesh into a bowl, and add one cup of water. Then squeeze handfuls of the grated nut so that the water becomes white and takes up the juices from the flesh. Go on doing this until you are convinced you must have squeezed out every last drop; this is likely to take at least a minute or so, but there is no need to spend an unreasonable amount of time on it. Then strain the liquid through a fine sieve, and squeeze the grated nut good and hard to make sure that all the liquid is out of it. Put the gratings back in the bowl, add another cup of water, and repeat the process; the more water you use, the thinner your santen will obviously be, but you should get a pint of thick santen from a nut. In most of the recipes in this book, that is about the thickness you require; if thicker or thinner santen is to be used, this is indicated.