One of the sweetest fruits of all, pineapple peaks for a day and then starts to deteriorate. You should sniff the bottom to see if there's a sweet (but not fermented) aroma and check to make sure that it feels heavy and firm. You can't ripen pineapples after they've been picked, so make sure to get a good one for your sauces, garnishes, salads, desserts, or special treats for the grill.