Air layering works on so this is a good indication that cuttings would probably also work if placed inside a mist box and rooting hormone was used. The fruit is ripe when the whole fruit turns purple. The outside skin also loses its gloss. They do not continue to ripen if picked green. They are overripe when the skin becomes wrinkled. If properly ripe they have a wonderful milk shake taste and milky colour. There are also green types of Star Apples. These are ripe when they turn to a golden colour. Both types also become soft, like an avocado, when ripe. – Oscar, Hawaii
This is a good site with info on how the star apple (referred to as milk apple) is eaten in Vietnam. It contains plenty of images. The site is extremely slow so for those with a slow connection, here is a copy of what it says:
No better word than marvelous can be used to praise milk apple, or star apple, a tropical fruit with the name Vu Sua (milk from the breast). Upon entering a milk apple orchard, the most famous located in Can Tho province in the Mekong Delta, visitors can see for themselves the hundreds of milk apples suspended from the branches. The round smooth fruit are all of equal size. The shape of the milk apple matches the name attached to it, as does its juice, which is fragrantly sweet and milky white. If visitors are unfamiliar to the region, the locals will guide them on how to enjoy the fruit. A novice will certainly peel the fruit with a sharp knife, which may cause the precious juice inside to be wasted. When using a knife to cut the fruit, it is advisable to cut the fruit into two parts before using a spoon to scoop out the pulp, bit by bit, until nothing is left. The most popular way to enjoy the fruit by orchard owners is to eat the whole fruit. People tend to drill a small hole at the top of the fruit, lift it to their mouths, lean their heads backward, and drink the flow of the fragrant juice. One thing you should remember before taking in the juice is that you must squeeze the tough fruit until it becomes tender so that the juice mixes with the meat of the fruit to become a sweet and fragrant muddy substance that looks like breast milk.