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When making blackberry jam, you can follow the same recipe as always but omit the pectin. Blackberries have enough natural pectin to set up by themselves. I learned this tip from my grandma, who had always made blackberry jam this way.
By Kay from North Bend, WA
I make jam all summer and autumn long and have never used separate pectin for setting. Lemon can be added to some fruit for extra setting quality, but I've never had to resort to additional pectin. If a fruit is known not to set well, then you only have to make sure you pick some slightly under-ripe fruit and add to the ripe ones for a set to be achieved.