MarkV

The acid of what? Jell-o mix contains acid already. The fruits were strawberry and pumpkin.

It was one box of jello and one tablespoon of Cooking Illustrated's pre-prepared xanthan gel. What proportion of jello/gelatin to xanthan gum could cause it to fail entirely to set? I'm wondering if maybe it was somehow too much liquid. Are gelatin hydrocolloids a thickness continuum, or is there a tipping point where it suddenly goes from somewhat set to not set all?

Common pectin doesn't set without sugar, and I didn't have any of either kind anyway, and in principle either gelatin or XG should work (but differently of course).

I have tried fresh strawberries and canned pumpkin puree.

There isn't really a recipe. I was looking to make jam without adding sugar and saw this and this and I had both jell-o and xanthan gum and I've used gelatin and XG together in ice cream so I thought I'll try them together. It didn't work at all. The result is just totally a flowing liquid. This seems to indicate the prevent each other from gelling.

I was playing around with various formulations of sugar-free jam and tried three times to combine xanthan gum and gelatin. It failed to set every time. Hot water, gelatin (Jell-o actually), xanthan gum, fruit pulp. Is there some interaction that prevents it from setting?

It's very hard to get a good picture with something so small but I attached a few. It's been wrapped in a black tea towel (I though the contrast would make for easier monitoring) and I scrapped it off at when stirring so is it possible that it's just lint?