To make a traditional grape pie filling, use only grapes, sugar and a thickener. Tapioca works well with as a thickener, but some cooks prefer to thicken with cornstarch or flour. Any variety of grape can be used, but Concords are preferred.
Wash 5 1/2 cups of Concord grapes, and remove the skins by squeezing the end oppose to the stem. The pulp should slide out easily. Set the skins aside, and place the grapes in a heavy saucepan with no water. Bring the pulp to a boil for five to six minutes to loosen the seeds, and then pass it through a colander or food mill. Pour the seedless pulp over the skins and allow to sit for five hours.
Stir 1 tablespoon of tapioca and about 1 cup of sugar into the grape mixture. If the grapes are tart, use a little more sugar. Pour the mixture into an unbaked 9-inch pie crust, and dot the filling with butter. Attach the top crust, and sprinkle lightly with sugar.
Bake the pie in a 450 F oven for 15 minutes. Reduce the heat to 350 F, and bake for about 20 minutes until the crust browns and the juice begins to bubble.