For the grape jelly, rinse the grapes under cold water. Allow to drain. Pluck the berries from the stems, remove the skins, cut them in half and pit them. Place the berry halves in a sieve or use a juicer to squeeze the juice into a container.
If necessary, add water to make up to 1 liter of juice. Pour into a saucepan with preserving sugar.
Bring to a boil while stirring and boil for 4 min on the stove. Stir in the juice of one lemon and bring to the boil again.skim off.
Quickly pour the grape jelly into sterile jars and close them tightly.