- Sterilize canning jars, and prepare two-piece canning lids according to manufacturer’s instructions.
- Separate pulp from skins of grapes. If desired, chop skins in a food blender or chopper.
- In a large pot, cook skins gently 15 to 20 minutes, adding only enough water to prevent sticking (about ½ cup).
- In a separate pot, cook pulp without water until soft. Press through a sieve or food mill to remove seeds.
- Combine pulp, skins and sugar. Bring to jellying point, about 10 minutes. As mixture thickens, stir frequently to prevent sticking.
- Fill hot jam into hot jars, leaving ¼-inch headspace. Wipe rims of jars with a dampened clean paper towel, and adjust two-piece metal canning lids. Process in a boiling water canner, following manufacturer’s instructions. The recommended process time for grape jam in a boiling water canner is 5 minutes for half-pint or pint jars.