We had so many blackberries this year that it became ridiculous. I was picking them and giving them away, making blackberry and apple pies and crumbles and freezing them.
I finally decided to make some jam/jelly with them, and proceeded to crush berries in a sieve to remove as many seeds as possible. I crushed enough to come up with 4 cups of juice (about 2 quarts of berries).
I used the Certo recipe , although I wasn’t worried about a few seeds winding up in the jelly, so I did not bother with straining it through cheesecloth. I followed the rest of the directions, however.
The jelly is delicious.