The dark purple grape juice sold in your local supermarket is most likely made from Concord grapes or a blend that includes Concords. Concords are sweet, with the familiar grape taste. If you don’t have grapes in your own garden, you can buy Concord grapes at your grocery store or look them at pick-your-own farms. An electric juicing machine makes short work of processing the grapes into juice; simply follow the instructions for your machine. However, if you are without a juicer, the old-fashioned juice-making method requires only simple cooking and straining.
Wash the Concord grapes under cold running water.
Remove the grapes from their stems, as well as any stray leaves or tendrils that may be present.
Place the clean grapes into a large pot and crush them slightly with a large spoon or potato masher. The object is to break the grapes' skins so that the juice will flow quickly from them.
Add 1 cup water per gallon of crushed grapes to the pot.
Simmer the grapes over low to medium heat for 10 minutes. Stir occasionally to keep them from sticking to the bottom of the pan. Skins, seeds and pulp will separate and float in the juice.
Strain the grapes through a jelly bag or juice strainer into a clean bowl. If you don’t have a jelly bag or juice strainer, line a colander with two or three layers of cheesecloth or a layer of clean muslin, set it over a large bowl and pour the juice through.
Discard the stems, skins and pulp.
Sweeten the grape juice to taste by stirring in sugar, honey or other sweetener while the juice is hot; this will allow the sweetener to dissolve easily.
Pour the grape juice into containers and refrigerate.