1 1/2 quarts blackberries (roughly)
5 cups of sugar
1 package of Liquid fruit pectin
3/4 cup of water
canning jars & lids!*
*Since this is freezer jam, your jar lids do not need to be brand new as you really aren't making a seal. However, be sure to sterilize and thoroughly clean your jars before filling them, as you can still end up with toxins inside. The amount of jars you need varies on the size of the jas you are using - anywhere from 2 quart jars to 6-7 smaller ones.
Crush fruit carefully - you don't want to overcrush, and you don't want to undercrush. I use a potato masher. (This is a great kid friendly part of the job, but remember blackberry stains fabric easily, so be sure kids are wearing playclothes and they can't ruin any tablecloths, etc) Next, measure three cups of the crushed fruit into a large bowl.
Next, stir in the five cups of sugar - you can use less, I usually use only 4, but the original canning recipe used 5, and allow to sit on the counter for 10 minutes. (This lets the fruit absorb the sugar)
Next, you'll want to stir this pectin mixture into your fruit and sugar mixture. Continue stirring this for about three minutes.
Now you're ready to add to your jars! Pour the fruit mixture into your canning jars, leaving at least 1/2 inch headroom at the top. Wipe off any fruit mixture that's gotten onto the side. Pop your lids on the jars, and sit on your counter on a safe space out of direct sunlight for 24 hours. (Set an alarm if you have to, because you don't want to leave them any longer than this, or it can invite problems!)
When the 24 hours are up, place in your fridge for up to 3 weeks, or in your freezer for up to 6 months. Remember, this jam is NOT shelf stable, so if you are gifting it to anyone, be sure to let them know to keep it in the fridge or freezer.