Remove all stems from the grapes and wash the them very well.
Place them in a blender. Pulse a few times until you get a coarse purée.
Add the blended grapes, sugar, and fresh lemon juice to a heavy-bottomed sauce pan.
Cook on a medium high heat, uncovered, until the juices start to thicken, making sure to stir often. This should take about 15-20 minutes.
Test to see of the jam is ready by scooping a ladle of the jam and pour it back slowly into the pot. You want it to be syrupy and not a loose runny liquid. If it’s too runny, continue to cook for a few more minutes until you get the right consistency - it will also thicken slightly when cooled.
Pour the jam through a strainer if you like it smooth.
Ladle into jar(s) and refrigerate once cooled. Keeps in the refrigerator up to 5-6 weeks.