I recently purchased a flat of blueberries, which is 12 pints. Unlike some other lucky people I know, I do not have blueberries growing in my yard, though I really should work on making that change. Anyway, I used about 6 1/2 pints for this recipe, which is straight from the Ball Blue Book. That's the Bible of canning, for those who don't know.
Pick through berries, discarding stems and mushy berries, if there are any. Rinse. Crush! I used a potato masher, and just took all of my troubles out on those poor berries. I think a food processor might work also. Or a blender. Just coarsely crush them, unless you don't like pieces of fruit in your jam, in which case, you should be making jelly.
9 c. crushed blueberries
6 c. sugar
Combine and bring to boil in a large pot. Boil hard, stirring to prevent sticking, until the mixture gels.
How will you know?
Put a small plate in your freezer. Remove pot from heat. Place a spoonful of jam on the plate and return it to the freezer. After it cools for a minute or so, run your finger through it. Does it leave a space? Then it's done! Time to can. If not, put your jam back on the heat and keep boiling. You know what jam looks like. You may have to test it a number of times. It took at least 20 minutes for mine, maybe even longer.
I bought an awesome canning kit at Wal-Mart a few years ago. It looks like this. I really recommend this if you are starting out. It comes with the Ball Blue Book, jars, lids, a funnel, etc. Everything you need, in one box. For more information on how to can, check here.
If you have a friend who cans their own goodies, I bet that he or she would love to have some extra help on canning day, and would show you how it all works.