Jello is a colloid. Colloids are stable herogeneous mixtures that do not separate over time. Pineapple and some other fruits contain too much citric acid which destroys the colloid suspension therefore it will not “set”. You can see the same effect if you add lemon juice to milk…it separates the milk into the casein protein and whey. The only suggestion for this is to be sure to dry the fruit off as much as possible before mixing so there is less acid present.
I think there are enzymes in those fruits that won’t allow jello to set.
they contain an enzyme that inhibits the jelling process
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Jello is a colloid. Colloids are stable herogeneous mixtures that do not separate over time. Pineapple and some other fruits contain too much citric acid which destroys the colloid suspension therefore it will not “set”. You can see the same effect if you add lemon juice to milk…it separates the milk into the casein protein and whey. The only suggestion for this is to be sure to dry the fruit off as much as possible before mixing so there is less acid present.