Put 2 to 3 pounds of Concord or wild grapes into a pan and bring water up just until you can see it under the grapes. Heat to a simmer without boiling and simmer for 10 minutes or so, crushing grapes with a potato masher once or twice. Strain the juice through a jelly bag, let sit overnight and strain again.

Measure 4 cups grape juice and 3 cups sugar into a large pan. Bring to a boil and boil, stirring constantly until the mixture sheets from a spoon. Skim the foam and pour into sterilized glasses or jars and seal with wax or lid.