Note: I’ve followed this recipe for 2 years in a row now with excellent results. The key is to just warm the berries. Don’t let them cook too long or they will lose their shape.
This is the way I made my filling. It was a lot less work than the Ball canning book called for.
7 cups blueberries
1 2/3 cups granulated sugar
2/3 cup ClearJel, cornstarch, or flour (as a thickener)
Blue & red food colorings
2 tbsp lemon juice
Combine sugar and your choice of thickeners in a large saucepan. Whisk in 2 cups of water. Add blue and red food coloring to get the purple color you like.
Note: I used flour because it was all I had and it worked just fine. It was certainly not as transparent as filling made with ClearJel or cornstarch. I would recommend the ClearJel if you have it and cornstarch if you don’t, with flour being a last resort.
Bring mixture to a boil over medium high heat. Stir often as it won’t take long to start to thicken. When it starts to thicken and bubble stir in the lemon juice.
Add the blueberries and keep over medium-low heat until berries are heated through.
Ladle into hot jars leaving just over 1 inch of headspace. Wipe rim, place lids, and process in a water bath for 30 minutes.
Yield: About 4 pints.