When wild plums are ripening, many gardeners eye them with a specific purpose in mind. Making wild plum apple jelly is a rite of summer that puts these wild plums to use in a delightful way. Wild plums are tart and have a significant amount of natural pectin in them, which makes them ideal for making jams and jellies. When you pair wild plums with apples, the jelly you make will be a family favorite.
Coarsely chop the apples and plums, keeping the pits and the cores of each. Place the coarsely chopped fruit into the stockpot and add the water.
Boil the fruit and water slowly, stirring occasionally. Cover and simmer the fruit for 30 minutes. Remove the fruit from the heat after 30 minutes.
Pour the hot fruit through a damp jelly bag or through damp cheesecloth to separate the juice from the fruit. Allow the fruit to sit in the jelly bag or on the cheesecloth for at least eight hours to strain completely. Do not push the fruit through the mesh of the jelly bag or the cheesecloth because this will push fruit pulp into your juice.
Pour the juice into the glass measuring cup after leaving it to sit for eight hours. Measure the juice and pour the juice into the stockpot. Add an equal amount of granulated sugar. Add 3 tbsp. of lemon juice to the stockpot for every 2 cups of plum juice.
Wash the jars in sudsy water and rinse them. Fill the water-processing canner with water and place the jars in the canner. Place the canner on a burner and begin to heat this water. Keep the jars in the hot water until you are ready to fill them.
Place the stockpot onto the stove and turn the burner to medium-high. Stir the juice mixture and heat it until it boils. Continue stirring and boiling for 10 minutes. If foam appears at the top, skim this off with the spoon.
Boil the jelly until it reaches 220 degrees F. Remove the stockpot from the burner when it reaches the required temperature and allow it to sit for one or two minutes. If another layer of foam appears, skim this off. Keep the burner turned off, but place the stockpot back on the burner to keep it warm while you place it into jars.
Pour the jelly into the prepared jars, leaving ¼-inch of free space at the top of each jar. Seal the jars and process them in a water processing canner for five minutes. Remove the jars from the canner and allow them to sit undisturbed for 24 hours on the counter.