To prepare juice. Select about one-fourth underripe and three-fourths fully ripe grapes. Sort, wash, and remove stems from 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. Add sugar and stir well. Boil over high heat to 8 degrees above the boiling point of water (220 degrees), or until jelly mixture sheets from a spoon. Remove from heat; skim off foam quickly. Pour jelly immediately into hot containers, seal and process 5 minutes in boiling water. Remove jars; cool and store. This recipe yields 5 six-ounce glasses.