Not sure about the how, but it appears that in Germany they make some sort of spirit out of them. So they can be fermented at least.

If you usually ferment beer I’d try and substitute some (boiled or baked and mashed) for part of the grain. Just remember that they’re like 18% carbs or so, so you’ll need quite a lot. And don’t forget the rice hulls, to prevent a stuck mash.

Wikipedia also says that when they’re stored, inulin converts into fructose, so if you have some lying around from last season maybe try those first.

Fair enough, there goes the enzyme theory then. So then probably just what’s in it.

Did you use raw pineapple juice or was it heat treated in some way? Raw juice would contain some enzymes that break down proteins and the resultant fragments could increase foaming. Just a random thought though, I’d be curious if cooking it reduces the effect.

Only used pineapple myself as freshly juiced, a tiny bit for bottling kombucha, instead of sugar for carbonation.

Otherwise, could be the fruit contains some unfermentable poly-sugars that increase foaming.