Canning method
Combine the currant juice and currants in a large saucepan. Add 4 cups of the sugar and cook for 5 minutes. Transfer to a glass or food-grade plastic container, cover loosely, and let stand for 12 hours or overnight in a cool place.
Prepare jar lids. Return the mixture to a large saucepan and add the remaining 3 cups sugar. Bring slowly to a boil, stirring until the sugar dissolves.
Boil rapidly to the gelling point, 220°F, about 30 minutes. Stir frequently as the mixture thickens to prevent sticking.
Pour preserves into hot pint or half-pint jars, leaving 1/4-inch headspace. Wipe jar rims and apply prepared two-piece lids.
Processing: Process pint or half-pint jars for 10 minutes in a boiling-water canner. Yield: about 9 cups.