Q: Why do green persimmons taste so bad?

A: Because they have a lot of tannin in their juice. One web site says “tannin coagulates the viscous protein on the surface of our tongues, leading to the astringent taste.” Anyone who has eaten one can testify to the yucky taste. One way to make sure persimmons are fully ripened is to store them in a bag with a very ripe apple or banana. The gas the fruit give off will help convert tannin to a form that doesn’t taste so bad.