Here are the white sapotes I got last week finally ripe (minus one that I ate just to see what they tasted like a bit earlier). As you can see, they've collapsed pretty sadly there.
Even more sadly, that liquid outer layer is nastily bitter. I understand that some varieties don't have that problem; this one has it in spades. I had to carefully wash off all that gunk while trying to retain as much of the inner flesh as possible. One was gunk all the way through. Then I had to remove the quite large seeds leaving only around a half cup of usable fruit and around two cups of waste. No wonder these haven't been commercialized.
Still, a half cup is enough for ice cream if I bolster the fruit with supporting flavors. The sapotes taste of lemon and vanilla with perfumy honeysuckle notes so it should be easy enough to work with.
The sapote pulp went into the blender with:
1 cup heavy cream
1/2 cup milk
1/2 cup thick coconut milk
1/2 cup slightly-brown sugar
juice of 1/2 lemon
1/2 teaspoon vanilla
1 large pinch salt
1 Tablespoon agave nectar
The result is nicely thickened right out of the blender which is a pretty good sign. The flavor is a lovely lemon custard, but mild so I added another Tablespoon of sugar to bolster it for the freeze. Actually there may have been a bit more sugar and agave nectar than that; I didn't measure. I'm not sure about the vanilla either. And, yes, the results taste of lemon, vanilla and agave, but I could tell there was something more in there. I'm not sure if anyone else will be able to after churning, though.
The churning itself didn't go as well as I had hoped. I think it's time to start moving the churn from my hot kitchen into my cool living room before using it. I don't think there's anything chemical in this mix keeping it from thickening up, unless there's something weird in white sapote that I don't know about so it's probably just the heat.
The mix did get cold enough for a smooth texture even if I wasn't able to churn in much air. That just means it's got that super-premium density. It might freeze up kind of hard. Guess I'll find out tomorrow...
You can't really tell from the picture, but the texture turned out quite well--smooth, creamy and resistant to melting. All without a custard or cornstarch. That's interesting. I think the coconut milk is more important to this effect than the sapote, but I'll have to do a test to be sure. (What I ought to do is make batches of a simple vanilla Philadelphia-style ice cream substituting in increasing amounts of coconut milk for the dairy to see how it affects the texture. A shame I don't work at an agricultural college; I could get funding for that.) There are some unpleasant fibrous shards in there unfortunately. I must have missed a bit of seed when I was cleaning the fruit.
The flavor is more intense than it was in the unfrozen mix which is also unusual. Like I said earlier, there are notes of vanilla and lemon, but the fruit is in there too with a richer underlying flavor tying them together. There are malty notes and some banana in there. Maybe a bit of custard too, although I think the name custard apple comes more from the texture than the flavor. It's complex and it shifts over the course of a mouthful from round fruit flavors up front to more citrusy notes at the end. Really very nice; it went over quite well at the office. This is no particular surprise, though. Ice cream is a standard use for white sapote and lemon and vanilla common flavors to pair it with. New to me, though.