Pour water into a large stainless steel kettle, and bring to a boil.
Do not core or peel apples, as the seeds, cores, and skin contain the lion's share of pectin.
Just cut them in half, lay them cut-side down on a cutting board, and, using a long knife, cut halves into slices and put them right into the pot.
When all the apples are in the pot and water is boiling fast, reduce heat, cover, and simmer for 30 minutes; apples will be very soft.
Fit a colander with 6 layers of rinsed cheesecloth.
Drain apples in colander over a large bowl (without pressing on fruit if pectin is to be used in the making of clear jelly) for 10 to 12 hours.
Pour juice into a medium-size saucepan, and reduce to two-thirds the original volume by boiling rapidly, uncovered.
Cool liquid.
Pour 2/3 cup into individual freezer containers, and freeze until needed.