Wash and stem the grapes
Crush the grapes in a large pot
Cook the grapes over medium heat until soft
Press the mixture through a sieve or food mill to remove skins and seeds
Measure the grape pulp
Add sugar to the pulp
Add lemon juice
Stir until the sugar dissolves
Bring the mixture to a boil
Cook until the jam reaches setting point
Skim off any foam
Test the jam for doneness
Pour the hot jam into sterilized jars
Seal the jars tightly
Let the jars cool completely
Store in a cool, dark place