I prefer to use a Steam Juice Extractor to get the maximum amount of tasty juice from the plums. It processes a large amount of fruit with a minimum amount of hassle, and the resulting pure fruit juice is rich and thick with a luscious viscosity that makes it perfect for jelly.
If you prefer a more natural jelly and don't mind spending the extra time it takes to watch for the jelly to reach the jelling stage, try my recipe for "Perfect Plum Jelly (without using pectin)".
Btw, this is considered a reduced-sugar recipe.
Makes ~6 half-pints
Note: Prepare canning jars before starting your preserving project.
1.) Pour juice into a heavy-bottomed preserving pan. Gradually stir in pectin with a whisk.
2.) Bring mixture to a full rolling boil that cannot be stirred down, over high heat, stirring constantly.
3.) Add sugar, stirring to dissolve.
4.) Return mixture to a full rolling boil, then boil hard 1 minute, stirring constantly.
5.) Remove from heat. Skim foam from the jelly of neccesary and ladle the jelly into clean warm jars, leaving 1/4" headspace.
6.) Wipe rims, then place lids on jars. Screw bands onto jars until finger-tight and process for 10 minutes in a Boiling Water Bath.
7.) After processing, set jars aside to cool undisturbed for 24 hours. Check seal, and it it's concave, store in a cool dark place for one year. If seals didn't take (or if they pop back up when you press down on them) just stick the jar in the fridge.