Prepare home canning jars and lids according to manufacturer’s instructions for sterilized jars. Keep jars and lids hot until filled. Always use new lids.
Place the grapes in a 1-quart jar. Add the sugar. Pour boiling water into the jar about halfway to ⅔ full; stir well to dissolve the sugar. Add enough additional boiling water to fill the jar, leaving ¼-inch of head space at the top. Use a damp cloth to wipe any drips from the top and sides of the jars. Cover with a hot lid and tighten ring firmly.
Repeat this process with as many jars and grapes as you like.
Set the hot jars on a rack in a canner or in a large pot of boiling water. The water needs to cover the jars by at least 1-2 inches. Boil the jars for 10 minutes.
Remove the jars from the boiling water and set on a towel or rack to cool overnight.
When cool, check the seals. The lids should be down in the center or stay down when pressed. Store in a cool, dark, dry place for at least 3 months or up to 1 year. When ready to use the juice, strain the liquid, discard the solids, and store in a clean jar in the fridge for up to 1 week.
Notes
Scale the recipe to make as many jars of juice as you like. You can prepare one jar at a time if you just have a small batch of grapes, or you can prepare many jars to enjoy throughout the year.
For the most robust flavor, allow the juice to sit for at least 3 months before straining and serving.
Barbara says that you can reduce the sugar in this recipe; however, I have not tested a lower-sugar version. We think it has just the right amount of sweetness as written!
To can the juice in half-gallon jars (instead of quart-size jars), the process is the same. You'll need 2 cups of grapes and 1 cup of sugar in each half-gallon jar, as well as boiling water to fill. Process the larger jars in a hot water bath for 15-20 minutes.
Use any fine mesh sieve or strainer to separate the solids from the juice. We have these mason jar strainer lids that are so convenient!