
Pineapple syrup is pineapple juice or fruit cooked down with sugar into a pourable syrup.
Pineapple with sugar, and cooking is what makes it a syrup rather than a juice — thicker, sweeter and stable. Anything thinner lengthens the drink instead of sweetening it.
Pineapple juice
The uncooked original: thinner, sharper, and still carrying the active enzyme. Not interchangeable by volume either, since the syrup is far sweeter.
Cream of coconut
Cream of coconut is reached for in the same tiki drinks and comes already heavily sweetened, and trading one for the other changes the sugar and the texture together.
Pineapple ferments more readily than most: homemade keeps about ten days chilled, and bubbles climbing the side are the first sign. A sealed bottle is good for months.