To freeze whole Concord grapes, rinse them in cold water, lay them in a single layer on a baking sheet and let them freeze until firm before packing them into freezer containers. To freeze Concord grape juice, pour the juice into freezer containers, leaving room for expansion.
You can leave the grapes on the stem if you are freezing Concords whole to enjoy as a cold snack. Frozen grapes will last for several months and even up to one year.
To make grape juice, pop the pulp from the skins. The pulp goes in one pot, and the skins (or hulls) go in a second one. Bring the pulp to a boil, and then strain it through a fine sieve or cheesecloth into the pot with the hulls. Return the mixture to a simmer. Once the hulls are soft, strain the grape mixture through cheesecloth. Stir in enough sweetener to suit your taste before pouring the juice into freezer containers. Stir well to completely dissolve the sweetener.
You can freeze grapes to use as filling for Concord grape pie as well. To do so, make grape juice, but don't strain the hulls out of the juice. Freeze about 2 1/2 cups of the grape mixture in a sealed bag. This is enough to fill a 9-inch pie.