Billyporter (Sally) shared a recipe for canning Grape Juice with us in the Summer Weather thread...
Grape Juice
I fill a quart jar with 2 c. of grapes. Fill to almost the top with boiling water and water bath can for 20 minutes. In six weeks it's basically ready to drink. I only add about a half cup of sugar to a gallon of juice. I can drink mine tartish. I also add water if it was a good year and the grape flavor is strong.