Working over a medium sized saucepan, cut a slit in the top of each grape on the stem end and squeeze out the pulp/seeds into the pan. Place the skins in a blender and set them aside.

Cover the pulp/seeds with about 1/2 inch of water, then place the pan on a burner set to medium-high heat.  Bring the mixture to a boil, then reduce it to a simmer. Cook the mixture, stirring occasionally, until the pulp breaks down and the seeds separate from it, about 15-20 minutes.

While the pulp mixture is cooking, add just enough water to the blender to cover the skins, then blend until mostly smooth and the skins have been broken down into very small pieces. Leave this in the blender for now. 

Place a sieve over a medium sized bowl. Strain the pulp and seed mixture through a fine sieve. Press with a wooden spoon to extract as much juice as possible. Discard the seeds and pulp pieces in the sieve. Return the strained juice mixture back to the pan along with the blended up skins. Stir in the maple syrup and spices and set the mixture over medium-high heat. Once the mixture comes to a boil, reduce the heat to medium to maintain a simmer and cook for 30-60 minutes, stirring regularly to keep it from burning on the bottom, until it thickens to an apple butter-like consistency. 

Once the mixture has thickened, remove it from the heat and put it into a clean jar.  Store the butter in the fridge.  It will keep for several weeks. Makes about 1 cup.