- 4 cups blueberries, mashed (about 2 1/2 pints)
- 1/2 cup sugar
- 1/4 cup lemon juice
- 1 teaspoon calcium water (packaged with Pomona’s Universal Pectin)
- 1 teaspoon Pomona’s Universal Pectin powder
- Sterilize five 8-ounce jars, keep hot. Prep lids and rings. Fill water bath canner and bring to boil.
- In a small bowl, mix together sugar and pectin powder. Don’t skip this step, or your pectin will clump. Set aside.
- In a large, non-reactive pot, combine blueberries, lemon juice, and the calcium water. Bring to a full boil.
- Add sugar-pectin mixture, stir constantly for 1-2 minutes while cooking to dissolve pectin. Return to boil, and then remove from heat.
- Ladle the blueberry jam into sterilized jars, leaving 1/4″ headspace. Wipe rims clean and screw on the lids. Process for 10 minutes in water bath canner (add 1 minute for every 1,000 feet above sea level).
- Remove jam from canner and place on a towel on the kitchen counter. Allow jars to cool completely. Test for seal. (Lid should not flex when pressed in the center.) Remove canning rings, wipe down if needed. Date and label, store in a cool, dark location.
Jam will last about three weeks once opened. Makes around 4 cups.
I always prep an extra clean jar for any left jam that doesn’t fit in the main jars. I scrape the jam from the bottom of the stock pot into this “extra” jar, too, since it tends to cook a little more and get thicker. We cover this jar and keep it in the refrigerator to use up first.