Yesterday I cut myself some fresh pineapple , then promptly proceeded to eat a lot of it before remembering that every time I eat a copious amount of pineapple, the roof of my mouth becomes itchy and sore. So why is this condition a common complaint among fresh pineapple aficionados?
Pineapples contain an plant protease enzyme called bromelain. Because it readily breaks down protein, bromelain is frequently used as a natural meat tenderizer. In addition, bromelain may also induce a prickly sensation in the mouth when consumed.
Although the enzyme is present in all parts of the pineapple plant, it's most concentrated in the stem, the hard piece in the middle of the fruit, which is much more fibrous and chewy but still edible. Many people believe that letting a pineapple sit overnight  helps take away the irritation factor, but one surefire way to alleviate the burn is to cut out the core.