When we visited Hawaii a few years ago one of the islanders advised us on how to get your pineapple sweet.
He said after you purchase a pineapple take it home and carefully break the top off the pineapple. Turn the pineapple upside down where the plume of leaves were and leave it for three to five days.  Then cut open your pineapple and it will be at its sweetest point. You know what? It works every time.