To prepare juice. Sort, wash, and remove stems from fully ripe grapes. Crush grapes, add water, cover, and bring to boil on high heat. Reduce heat and simmer for 10 minutes. Extract juice. To prevent formation of tartrate crystals in the jelly, let juice stand in a cool place overnight, then strain through two thicknesses of damp cheesecloth to remove crystals. To make jelly. Measure juice into a kettle. Stir in sugar. Place on high heat and, stirring constantly, bring quickly to a full rolling boil that cannot be stirred down. Add pectin and heat again to a full rolling boil. Boil hard for 1 minute. Remove from heat; skim off foam quickly. Pour jelly immediately into hot, sterile canning jars to 1/4-inch from top. Seal and process 5 minutes in a boiling water bath. This recipe yields 8 or 9 half-pint jars.