If using grapes, wash and crush them in a large pot.

Cook the crushed grapes over low heat until they soften and release juice.

Strain the cooked grapes through a fine mesh cloth or strainer to get clear juice (about 5 cups).

If using bottled grape juice, skip the crushing and straining steps.

Pour the juice into a deep pot and mix in the pectin with a small amount of sugar.

Bring the mixture to a rolling boil, stirring constantly.

Add the remaining sugar (4 cups) and stir until fully dissolved.

Return to a full boil and cook for exactly 1 minute to activate the pectin.

Remove the pot from heat and skim off any foam that forms on top.

Pour the hot jelly into sterilized jars, leaving about ½ inch of space.

Wipe the rims clean, seal the lids tightly, and let the jars cool at room temperature.

The jelly will thicken and set as it cools.

Store unopened jars in a cool, dark place for up to 1 year.

Once opened, refrigerate and use within 3 weeks for best flavor.