Eggplants, like watermelons are difficult to tell when they are ready for picking. It's better to pick them early as they are fine to eat then. Purple eggplants go dull looking when too mature, and I suspect Thai eggplants, although usually green and white, would also loose their sheen.
The recognised way to test whether an eggplant is ready is to press with your thumb and there should be a slight indentation left that will flatten out quickly.
If eggplants are left too late to pick, the seeds may swell up, the fruit goes hard and they will taste like cardboard.
Aug 23, 2012
Eggplant splitting by: Al
I think what we have here is more likely a response to heat and moisture stress, not over- mature fruit. I would remove all split fruit and allow the plant to try again. I have seen this when I have used earth boxes at the peak of heat and numbers of fruit on the plants overwhelm its capacity to cope. Then, when it rains, they split like some tomatoes do. The brown color is unappetizing to say the least, though if you have any normal parts you can cook and eat it.