Begin by washing and removing all stems from your grapes. Place into a pot and crush the grapes to release all their juice. Add enough boiling water to cover grapes and bring to a simmer. 

Simmer the mixture for 10 minutes until the grape skins have softened.

Strain this mixture through a jelly bag (or multiple layers of cheesecloth). Discard the grape skins and flesh and move the juice to the refrigerator, preferably in a large pitcher if you have one. Allow the juice to rest here for 24 to 48 hours.

After this day or so has passed, carefully remove the refrigerated juice and pour into a large pot, being sure not to disturb the sediment at the bottom of the pitcher. Discard sediment. For clearer juice, pour the liquid through a coffee filter to remove more sediment. (The sediment is tartaric acid crystals, and they can cause throat irritation if included in your juice. Many modern grape varieties are low in tartaric acid, but not all of them. It's always good practice to allow the juice to settle for 24 to 48 hours in the refrigerator before canning.)

Sample the juice and sweeten to taste. Heat this mixture of juice and sugar, stirring to dissolve sugar until the mixture comes to a boil.

Immediately, ladle hot liquid into freshly prepared jars leaving ¼ inch headspace. If canning, clean rims, apply 2-part canning lids, and process in a waterbath canner, adjusting for altitude. Canning times are as follows: If below 1,000 feet, 5 minutes for pint and quart jars (10 minutes for half-gallon jars). If between 1,000 and 6,000 feet, 10 minutes will be needed for pint and quart jars (15 for half gallon jars). If above 6,000 feet in elevation, process for 15 minutes (20 minutes for half-gallon jars).