Making Elderberry Juice for Jelly
Start by stemming the elderberries. They're easiest to stem if you freeze the whole sprays of fruit for at few hours (or overnight) first. Frozen fruit pop off the stems easily, and the freezing process helps them release their juice for jelly.
Once the elderberries are stemmed, place them in a saucepan with 1/2 cup of water. You'll need 11-12 cups of stemmed elderberries, or about 3 pounds of fruit, to get a yield of 3 cups of elderberry juice for this recipe.
Bring the elderberries and water to a simmer and cook them for about 5 to 6 minutes, gently mashing them with the back of a spoon to help them release their juices. Once the fruit have fallen apart, remove the pan from the heat and strain the mixture through a jelly bag (or a mesh strainer lined with 2 layers of damp cheesecloth).
Measure the resulting juice, you should have about 3 cups. If you have more than 3 cups, save the extra for another recipe. If you have less, add water or apple juice to bring the total up to 3 cups.
Making Elderberry Jelly
If canning, prepare a water bath canner, jars and lids before beginning.
To make elderberry jelly, place 3 cups of elderberry juice into a pot and add the lemon juice and powdered pectin. Do not add sugar yet. Adding the sugar early will prevent your jelly from setting.
Stir the pectin to break up any clumps and ensure it's fully dissolved.
Turn on the heat and bring the mixture up to a boil. Boil hard for 1 minute.
After the pectin/juice mixture has boiled for 1 minute, add the sugar.
Return the mixture to a boil and boil for 1 minute.
Remove from the heat and ladle into prepared jars, leaving 1/4 inch headspace. Seal with 2 part canning lids.
If canning, process the jars in a water bath canner for 10 minutes (or 15 minutes if above 6,000 feet in elevation). Once the processing time is complete, turn off the heat and allow the jars to sit in the canner for an additional 5 minutes before removing them with a jar lifter to cool on a towel on the counter (this helps prevent siphoning).
Allow to cool completely and check seals after 12 hours. Store any unsealed jars in the refrigerator for immediate use. Properly canned and sealed jars will maintain peak quality on the pantry shelf for 12-18 months, and be safe to eat as long as they're sealed. Refrigerate after opening.