Place the 4 quarts of grapes in an 8-quart stockpot on the stove and pour in 1 quart of water. Bring the grapes and water to a boil then turn down to medium-high heat and cook for approximately 20 minutes. When the grapes have cooked down into what looks like all liquid, it is ready to strain. Remove from the heat and allow to cool until are able to handle, about 1 hour.
Pour the cooked-down grapes into a heavy-duty cloth bag. The bag should be sitting in a bowl to catch all the juice.
Start squeezing and twisting the bag to bring out as much juice as possible. The debris left in the bag should be dry.
To the juice, add 1 ½ cups of sugar and an additional 1 quart of water. Stir and bring to a boil over medium-high heat. Boil until the sugar is dissolved, 5 minutes.
Pour into quart jars, leaving ¼-inch of headspace. Wipe the jar rims with a clean cloth and fit with lids and rings prepared according to the manufacturer's instructions. Place the jars in a water bath for 10 minutes to process, adjusting for altitude following the USDA guidelines.
Once processed, remove jars from the water bath and let sit 12-24 hours. Remove the rings and check the seal. Store at room temperature for up to 1 year.
To prepare the juice to drink, use ⅓ concentrate to ⅔ water or other liquid.
To strain the juice, a heavy-duty cloth bag works extremely well. If you are feeling adventurous, you can make your own out of feed sack cloth material. You want a heavy-duty bag since you will need to squeeze and twist it to get all the juice out.