[hamstergbert]

probably would  - I certainly have used something like 20% by weight of crabs in order to make sure of a good set jelly.  Much higher and you'll likely overpower the subtle fuchsia taste.

Bit early for picking them as yet, round here at any rate.  Typically mid August right through pretty well to the first frosts, picking the berries when they are black, juicy and each about the size of a small grape.  By the way, not up to much on their own until you jelly 'em, they certainly need to feature in part of a conserve/preserve.  Subtle taste faintly reminiscent of passion fruit.  Best feature however is unusualness, it has to be said!