Prepare the calcium water:Combine ½ teaspoon calcium powder (from the small packet in the box of Pomona’s pectin) with ½ cup water in a small jar. Screw on a lit and shake until well-combined. You'll have more than you need for this recipe. Store the excess in the refrigerator for use in making additional jam or jelly recipes.
Wash the jars you'll use, making sure each is clean and free of nicks in the rim, which could impede sealing.
Wash the lids and rings in hot soapy water. (If you're using non-Ball brand lids, prepare as suggested by manufacturer.)
Place empty jars in a canning pot or large stock pot with enough water to cover by an inch or two, cover pot, and set on high heat. It can take awhile for the water to heat, so get it started before you begin making the recipe.
MAKE THE GRAPE JELLY
Measure the grape juice, lemon juice, and 4 teaspoons of prepared calcium water into a large saucepan; bring to a full rolling boil. (Save the remaining calcium water in the fridge for a future batch of jelly.)
4 cups grape juice, 1/4 cup lemon or lime juice, 4 teaspoons calcium water
Meanwhile, combine the sweetener with the pectin until it's thoroughly combined.
When the grape mixture comes to a boil, stir in the pectin and sweetener, stirring vigorously for 1 to 2 minutes to dissolve the pectin while bringing the jelly back to a boil. You can use your immersion blender to do this, if you have one. Otherwise, whisk vigorously.
Remove from heat when the jelly boils.
CANNING THE JAM
Ladle hot jam into quarter-pint, half-pint, or pint sized jars, leaving 1/4" head space. A canning funnel makes this easy.
Wipe jar rims to remove any jam that may have spilled. A clean rim is essential to a good seal.
Set jar lids in place. Screw bands on finger tight.
Use a jar lifter to gently place jars into hot water in a canning pot equipped with a rack. Water should cover the top of the jars by an inch. The water will cool somewhat in reaction to the addition of the jars. Return the water to a simmer and then set the timer.
Process for 10 minutes 0-1,000 feet altitude; add an additional minute for every additional 1,000 feet in elevation.
Remove jars from water using the jar lifter and transfer to a solid, towel-covered surface. Allow to cool for 24 hours.
Check seals. Lids should be solid and pulled down tight. (if they flex and pop, the jar didn’t seal; put unsealed jars in the refrigerator and use those first).
Remove rings and wash outsides of jars. Store in a cool, dry place.
FOR REFRIGERATOR OR FREEZER JELLY
If you'll use the jelly within a month or so, you can just refrigerate it. In this case, you can fill the jars to within 1/4" of the top.
To freeze, use straight-sided jars and only fill them 3/4 full to allow room for expansion when frozen.
Screw on lid and allow to cool before placing jelly in the refrigerator or freezer.
Notes
This recipe is made using Pomona’s Universal Pectin. This is the only pectin I use anymore as it allows me to use much less sweetener. The standard pectin brands use an obscene amount of sugar in my opinion, often requiring equal amounts of sugar and fruit! This product uses a low methoxyl method and calls for using two different ingredients, which are included in the box: pectin (the large packet) and calcium powder (the small packet).
Boiling lids or heating above 180°F as once recommended can damage the sealing compound.