Remove both stem and blossom ends from crab apples. Do not peel or core.
In a large pot, bring crab apples and water to cover to boil.
Reduce heat, cover and simmer, stirring occasionally, for about 10 minutes or until softened.
Using potato masher, crush crab apples; cook for 5 minutes longer.
Suspend jelly bag or layered cheese cloth over a large bowl and secure (I used clothes pins).
Fill with crab apples; let drip, without squeezing, for about 2 hours or until juice measures 6-1/2 cups (1.625 L), adding up to 1-1/2 cups (375 mL) water if necessary.
In very large pot, bring juice with sugar to full rolling boil over medium-high heat, stirring constantly; boil for 15 to 18 minutes or until gel stage (122F). This may take much longer than 18 minutes.
To test gel stage, freeze several small plates. Put 1 tsp liquid on cold plate and return to freezer for one minute. (Remove pot from heat while testing). At gel stage, surface should wrinkle when pushed with finger. If not, continue cooking and test again in a few minutes.
A second test for gel stage is to dip a cold, metal spoon in liquid and see if it sheets off when lifted to drip.
It sounds complicated, but it seems to work out whether the tests work for you or not.
When gel stage is reached, remove from heat and skim off foam.
Using funnel, fill hot 1-cup (250 mL) canning jars, leaving 1/4-inch (5 mm) headspace. Cover with prepared lids. Screw on bands until resistance is met; increase to fingertip tight. Boil in boiling water canner for 10 minutes (or not, I don't bother).
Turn upside on counter for 12-24 hours and then test seals.