Prepare the cherries: If using fresh cherries, pit them. If using frozen, do not thaw. Combine cherries and water in a large, non-reactive pot. Bring to a boil, then reduce heat and simmer, covered, for 20 minutes, stirring occasionally.

Extract the juice: Strain the cooked cherry mixture through a jelly bag or several layers of cheesecloth set over a bowl. Allow the juice to drip slowly without squeezing for best clarity. Measure the resulting juice; you should aim for approximately 4 cups.

Activate the pectin: Measure 4 cups of the reserved clear cherry juice into a clean pot. Add the powdered pectin and bring the mixture to a full rolling boil, stirring constantly. Boil hard for exactly 1 minute.

Add sugar: Slowly stir in the granulated sugar, mixing until it is completely dissolved. Return the mixture to a full rolling boil that cannot be stirred down. Boil hard for exactly 1 minute.

Skim and jar: Remove the pot from the heat immediately. Skim off any foam from the surface using a metal spoon. Carefully ladle the hot jelly into sterilized canning jars, leaving 1/4 inch headspace.

Process: Wipe the rims clean. Apply lids and screw bands to fingertip tight. Process the filled jars in a boiling water bath canner for 10 minutes (adjusting for altitude), then remove and let cool completely before checking seals.