Wash and separate the grapes from stems.
Put them in a pressure cooker with 1/2 cup of water on low flame and cook till one whistle.
Open pressure cooker after 5 minutes and grind grapes into a smooth paste. It yields 1 & 1/2 cups of grape puree.

Now put boiled puree with 1/2 cup of sugar in a deep saucepan and cook on medium-low flame for 10 minutes.
Once jam starts to thickens switch off the flame.
Allow jam to cool down. Then add lemon juice and mix well.

Tips :

Lift jam with a spatula and pour jam, it should flow together and not in drops.
Pour few drops of prepared jam on a plate if it spreads then it’s not ready if it stays firm without moving then the jam is ready.
Allow jam to cool completely. Then store in a clean and dry glass jar.
Keep jam in the refrigerator after every use. Use a clean and dry spoon. It last long for 3 months.