Step 1: Wash grapes thoroughly and remove any stems. Discard any bruised or spoiled grapes.
Step 2: Sterilize canning jars and lids. Wash jars and rings in hot soapy water, rinse, and place jars in a large pot or canner. Cover with water and bring to a boil for at least 10 minutes. Keep hot until ready to fill. Simmer lids in hot water (not boiling) for a few minutes. (See notes for alternative sterilization methods).
Step 3: Place washed grapes and 1/2 cup water in a large, heavy-bottomed pot. Bring to a boil over medium-high heat. Reduce heat, cover, and simmer for 15-20 minutes, or until grapes are very soft. Mash grapes frequently with a potato masher to extract juice.
Step 4: Place a colander lined with several layers of cheesecloth (or a jelly bag) over a large bowl. Carefully pour the cooked grape mixture into the colander. Allow the juice to drip naturally for several hours or overnight. Do NOT squeeze the cheesecloth, as this can make the jelly cloudy. You should aim for exactly 5 cups of strained grape juice.
Step 5: Measure exactly 5 cups of strained grape juice into a large, clean, heavy-bottomed pot. If you have less, you can supplement with good quality store-bought grape juice.
Step 6: Stir the liquid fruit pectin into the grape juice. Bring the mixture to a full rolling boil over high heat, stirring constantly.
Step 7: Immediately add all 7 cups of granulated sugar at once. Stir continuously until the sugar is completely dissolved.
Step 8: Return the mixture to a full rolling boil, stirring constantly. Boil hard for exactly 1 minute.
Step 9: Remove the pot from the heat. Skim off any foam from the surface of the jelly using a metal spoon.
Step 10: Ladle the hot grape jelly into the hot, sterilized jars, leaving 1/4 inch of headspace. Wipe the rims clean with a damp cloth to ensure a good seal.
Step 11: Center the lids on the jars and apply the screw bands until fingertip tight.
Step 12: Place the filled jars into a boiling water canner. Ensure jars are covered by 1-2 inches of water. Bring to a rolling boil and process for 10 minutes (adjust for altitude if necessary).
Step 13: Carefully remove jars from the canner and place them on a clean towel or cooling rack. Allow them to cool undisturbed for 12-24 hours. Check seals: lids should be concave and not flex when pressed. Store sealed jars in a cool, dark place for up to one year. Unsealed jars should be refrigerated and consumed within a few weeks.