Sealing Jars/Preventing Spoilage of Jelly
Even though sugar helps preserve jellies and jams, mold can grow on the surface of these products. Research now indicates that the mold which people usually scrape off the surface of jellies may not be as harmless as it seems. Mycotoxins have been found in some jars of jelly having surface mold growth.
Because of possible mold contamination, paraffin or wax seals are no longer recommended for any sweet spreads, including jellies.
To prevent growth of molds and loss of good flavor or color, pour hot product into sterile Mason jars, leaving 1/4 inch headspace, seal with self-sealing lids and process 5 minutes in a boiling water canner.