Begin by washing the grapes thoroughly under cold water.

Using a potato masher, gently crush the grapes in a large saucepan.

Add the sugar and lemon juice to the mashed grapes in the saucepan. Stir to combine, and let it sit for about 10 minutes.

Stir in the fruit pectin and cinnamon (if using) into the grape mixture.

Place the saucepan over medium heat and bring the mixture to a boil, stirring frequently.

Once boiling, cook for about 10-15 minutes until the jam thickens.

Carefully ladle the hot jam into sterilized canning jars, leaving about 1/4 inch of headspace.

Process the jars in a boiling water bath for 5-10 minutes to ensure they seal properly.