I make elderberry jelly to put into yoghurt. It is a flavour that is very difficult to obtain commercially, and rather a nice flavour IMNSHO.
I also make Medlar Jelly though in recent years is is easier to make it into a syrup because once in yoghurt the texture is relatively unimportant, though can produce flavour concentrations, which is tasty.

I do think the enzyme digest theory is not really on, because the burnt toast has been sterilised - but who knows what is lurking in the not polished surface of the plastic. It is what they would call micro featured I think.
Maybe the charcoal is a bit like coke used as a catalyst in ammonia production because it has a large surface area of very sharp micro points, rather than any chemical reaction.