4 cups (800g) sugar
1 lemon, juice and zest of
2 tsps ground cinnamon
1/2 tsp nutmeg, freshly grated
6 oz. (170 ml or 2 packets) liquid pectin
Canning prep: Ready the boiling water bath and the clean (washed with soap and water) jars you plan to use for canning. Check your jars and lids for nicks or cracks – don’t use them if they have any because it could jeopardize creating a good seal. If using standard Ball or similar style jars, it helps to put them in the pot you plan to use for canning and fill them (and the pot) with water, then bring to a boil. Keep the jars at a simmer (180°F) until they are ready to use. Place the lids in a small saucepan with enough water to cover them and set to a simmer over low heat (high heat can compromise the gummy seal material). If using Weck jars, you only need to sterilize your jars and glass lids if they will be processed for less than 10 minutes. Place the rubber rings in a small saucepan of water and bring to a boil for 2-3 minutes then leave them in the hot water until you are ready to use them.
Make the blueberry jam: Combine the smashed blueberries and sugar in a large non-reactive pot. Bring the mixture to a boil over high heat. Add the lemon juice, lemon zest, cinnamon, and nutmeg to the blueberries and boil 15-20 minutes. Stir the jam frequently to avoid burning at the bottom of the pan. When the jam has thickened and looks shiny, stir in the liquid pectin. Let it return to a rolling boil for 5 minutes. Remove the jam from heat and start ladling jam into the jars, leaving 1/2-inch headspace.
Can the jam: Use a cloth to wipe the rims clean and apply the lids and rings of the Ball-style jars to fingertip tight (just tightened with fingertips – not super tight). If using Weck jars, place the rubber rings on the glass lids and set them on the jars. Secure the lids with two canning clamps for each jar – 180° from each other (across from each other). Set the jars in your canning bath (either on a jar rack or a makeshift cooling rack – just be sure they are not set directly on the bottom of the pot) and check that there is at least 1-2 inches of water above the lids of the jars – if not, add more water. Once the pot has returned to a boil, process for 10 minutes if you are at an altitude of sea-level to 1,000 feet above sea level (asl). For 1,001 to 3,000 feet asl, add another 5 minutes to the 10 minute processing time. For 3,001 to 6,000 feet asl, add 10 minutes to the 10 minute processing time. For 6,001 to 8,000 feet asl, add another 15 minutes to the 10 minute processing time. And finally, for 8,001 to 10,000 feet asl add an additional 20 minutes to the 10 minute processing time for a total of 30 minutes.
When the jams are done processing, remove them from the canning bath and place them on a towel-lined countertop to let them cool. Don’t mess with them! For the metal lids, you may hear the “ping” of the seals forming as the center of the lid gets sucked down. There will be no pinging of the Weck lids, but you may notice the tongue of the rubber band pointing down (this is good). Let the jars cool for 24 hours. Remove the bands or clamps and lift the jar an inch or so off your work surface (carefully – in case the seal is bad and breaks) by the lid. If the seal is good, it should hold. Store the jars in a cool, dark location for up to a year (take the clamps and rings off). Also, any jar with a bad seal can be stored in the refrigerator.
Alternatively, if you don’t want to can the jam, you can store it in the refrigerator (I think for up to a year). Makes 3 1-pint (500 ml) jars or 6 8-ounce (250 ml) jars.