This Blueberry Rhubarb Jam recipe won third prize in The 1983 Old Farmer’s Almanac Recipe Contest. Rhubarb adds a pleasant tartness to this jam, and the blueberries provide color and texture.
In a large sauce pan, crush the blueberries using a potato masher, then add the rhubarb, water, lemon juice, and sugar. Bring the mixture to a rolling boil for 1 minute. Add the pectin, stir well, and return mixture to a full rolling boil and boil for 1 minute.
Prepare boiling water canner and heat jars in simmering water until ready to use. Wash lids in warm soapy water and set aside.
Remove jam from heat and skim off any foam. Ladle hot jam into hot jars leaving a ¼ inch of headspace. Clean rims of jars before putting on jar lids. Screw the metal bands on finger tight and place in boiling-water bath canner. Process for 10 minutes.
Turn off heat and take off lid. After 10 minutes, remove jars and place on a rack or kitchen towel on the counter. Allow jars of jams to cool down without moving. You may hear pinging…the jars have sealed! After 24 hours remove the screw bands and test seal by pressing gently on the lid. Store for up to a year in a cool, dry place.