Wash 6 half-pint jars, rings, and lids and prepare canner by adding water to it.

Measure 4 cups of juice and pour it into a pot.

Combine pectin with 1/4 cup sugar. Add pectin mixture and butter to the juice and stir until dissolved. Bring the mixture to a rolling boil over high heat. Stir constantly to avoid burning.

Add the rest of the sugar and bring back to a rolling boil. Hard boil for 1 minute, stirring constantly. You should not be able to stir down the bubbles. Remove from heat. Skim off foam if necessary.

Using a funnel, ladle the jelly into clean jars, leaving 1/4 inch headspace. Wipe the rims with a clean cloth and put the lids on. Tighten rings to fingertip tight.

Start heating the water in the canner.

Put the jars in the canner and lower the rack. The water should cover the jars by about 1-2 inches. Add water if needed. Put the top on the canner and bring the water to a boil. Once it is boiling, process the jars for 10 minutes.

When the timer goes off, turn the heat off and let sit for 5 minutes. Remove the lid and remove the jars using a jar lifter. Let sit undisturbed for 12-24 hours and then check for proper seals. Store in a cool, dry place with the rings off.