Remove the grape skins from the grape pulp. You can do this by giving a grape a squeeze between two fingers. Place the pulp in a medium saucepan and the grape skins in a large bowl.
Once all the grape skins and pulp have been separated, place the saucepan with the pulp over medium heat. When the pulp comes up to a boil, reduce heat to low and let the pulp simmer until it becomes a liquid. It should take about 10 minutes.
Place the skins into a food processor and pulse it until the skins are coarsely chopped.
Add the skins in a stock pot with 1/4 cup water. Heat over medium heat until the skins come up to a boil then reduce to low to simmer. Let the skins simmer about 10 minutes.
Put the liquified pulp in a sieve or food mill over the stock pot with the skins and push the pulp through. Discard seeds.
Stir to combine the pulp and skins. Add in the sugar, lemon juice, and butter. Stir to combine ingredients.
Let the mixture come up to a boil over medium heat. Stirring occasionally.
Once the jam comes up to a boil, reduce heat to low and simmer until the jam is reduced and thickened. A sure way to tell if the jam is ready is put a plate in the freezer to chill. Once chilled, pull out and dab a spoon full of jam on it. Place back in the freezer for 1 minute. Push the sides of the jam with your finger and if it doesn't move it's ready!
Place the hot jam into hot sterilized jars. Wipe the rim with a damp towel. Place a hot lid on and ring. Tighten the ring down. Place into the hot water canner and make sure the water covers the lids. Once the water comes up to a boil, boil for 10 minutes. Remove from water and place under a warm towel. Let it sit overnight.