Wash grapes; drain and remove stems. Plunge grapes into rapidly boiling water to cover; boil 2 minutes. Drain well. Slip off grape skins, and grind skins finely, reserving pulp; set aside.
Place pulp in a flat-bottomed kettle; cook over medium heat 10 minutes or until seeds begin to separate from pulp. Press pulp through a sieve to remove seeds; discard seeds.
Return pulp to kettle; add reserved skins and remaining ingredients, stirring well. Cook over medium-low heat, stirring constantly, 30 minutes or until mixture thickens.
Quickly ladle butter into hot sterilized jars, leaving 1/4-inch headspace. Cover at once with metal lids, and screw bands tight. Process in boiling-water bath 5 minutes.