Prepare water bath canner. Wash jars and lids thoroughly in hot, soapy water and rinse well. Add jars to canner and cover with water 1 inch above the jars. Let jars sit in hot water until ready to use.
Pour boiling water over lids and let sit in hot water until ready for use.
Combine the fruit, juice or water and lemon juice in a large saucepan. Gradually stir in pectin. Bring mixture to a full rolling boil (one that can't be stirred down.), stirring constantly.
2 cups blueberries, 3 tsp lemon juice, fresh or bottled, 1.5 Tbsp Low Sugar Pectin, 0-1/2 cup Sugar, 1/3 cup fruit juice or water
Add sugar, if using. (see notes below) Return mixture to a full rolling boil that cannot be stirred down. Boil hard for 1 minute, stirring constantly. Remove from heat. Skim foam, if necessary.
Ladle hot jam into hot jars. Cool to room temperature, if not canning. Then refrigerate immediately.
If preserving, ladle hot jam into the hot jars, leaving 1/4" headspace. Wipe rims clean with paper towel.. Center lids on jars. Apply bands and adjust to fingertip tight.
Place filled jars in canner ensuring jars are covered by over 1" water. Bring to a gentle, steady boil.
Process jars for 5 minutes, under 1000 feet, adjusting for altitude. (see notes below) Turn off heat. Let jars rest in hot water for 5 minutes.
Remove jars and cool. Check lids for seal after 24 hours. Lid should not flex up and down in the center, when pressed. Store jars in a cool place.
Makes 2 half pints. If you use less sugar, the yield will be less.Recipe can be multiplied, but don't do more than 5 times the recipe. The jam has a tendency not to set properly. Test lids for seal. Pres center of lid down in the middle. If it flexes up and down, jar is not sealed.Store in a cool place.If lids have not sealed, store those jars in refrigerator and consume those jars first.Use up to 1/2 cup sugar. I usually use over 1/4 cup but under 1/2 cup of sugar.Altitude adjustment for half pints0-1000 feet – 5 minutes1000-3000 feet – 10 minutes3000-6000 feet – 15 minutesabove 6000 feet – 20 minutes