
Fresh pineapple juice is the sweet, acidic juice pressed from fresh pineapple flesh.
Good pasteurized juice is the practical stand-in: less bright, and it foams far less, since the proteins that build the head are damaged by heat. Mango or passion fruit fill the tropical role and change the fruit outright.
Pasteurized pineapple juice
Heating takes away its foam and mutes the aroma, but it also kills the enzyme — which makes it the safer choice in anything with cream that has to stand.
Pineapple syrup
Cooked and heavily sweetened. Not a volume-for-volume swap in either direction: the syrup is far sweeter and carries none of the acidity.
A day or two chilled. It separates as it stands and wants a stir before measuring, and it ferments faster than most juices, so a faint cider smell means it has started.