Measure out 7 cups of sugar into a medium bowl and set aside.
In a large saucepot combine grape juice, lemon juice and pectin.
Bring to a full rolling boil (will not stop bubbling even when stirred).
Once boiling, add sugar all at once, stirring well to combine.
Bring back to a full rolling boil and boil rapidly, stirring constantly for 1 minute exactly. Immediately remove from heat, skim off any foam and ladle into hot sterilized jars, filling to 1/8 inch from top.
Place sterilized tops and rings on jars and tighten rings firmly, but not as tight as you can.
Place jars in canner rack and lower into gently boiling water, covering tops of jars by two inches (add more water if necessary).
Place lid on canner and continue gently boiling for 5 minutes.
Carefully remove jars from canner and place upright on a towel-lined countertop or cooling rack and allow to cool completely.
As jars cool you may hear a pop! That’s a great sound, it means your jars are sealing.
After jars are completely cool, check seals by pressing tops of lids.
If the lid pops back and forth, the lid is not sealed and you must use immediately and refrigerate. Otherwise, you can follow the Sure Jell or powdered pectin box’s directions for re-processing.