I make jam all the time, using pectin. But the recipes only list a few dozen common fruits.
Recently, I wanted to make crabapple jam or jelly, and I found a recipe that essentially had me cook the whole fruit in water, juice it, add about an equal amount of sugar to the juice, and cook it to slightly above boiling (220 F).
I have some juiced oregon grape, and I want to make it a jelly, and I've found a page that sounds like it's the same idea as the crabapples: about equal amounts juice and sugar, boil to a jell stage.
So, can I do that with most sour fruits? I guess the question is essentially, do most sour fruits have enough natural pectin that they will jell without adding pectin? Is there any danger in experimenting? Or do I need to stick with normal fruits or at least existing recipes?