An Intro to Canning and Blueberry Jam

By: Marisa McClellan
blueberry jam

When it comes to canning, blueberries were my gateway fruit. During my childhood, I helped my mom make jam with the berries from our annual picking trip. Later, blueberry jam was the first thing I ever canned on my own (though I did call my parents for guidance at least seven times during the making of that initial batch). Spiced with a little bit of cinnamon, nutmeg and lemon zest, it tastes like home.

The beauty of blueberry jam is that it sets you up for success. Blueberries contain a lot of natural pectin, so even if you mash and measure imperfectly, nine times out of 10, you’ll still wind up with something spreadable and quite delicious.

What’s more, preparing blueberries for jamming is shockingly easy. All they need is a quick rinse, a careful once-over to remove any stems (don’t throw away the mushy berries, they work just fine in jam) and a thorough smashing. I find it quite satisfying to just plunge my hands in and start squashing. A potato masher is an acceptable substitute if you don’t like to get your hands covered in blueberry goo.

Once the blueberries are mashed, set them aside and prepare your canning equipment. Fill a large pot with water and sink a round rack or kitchen towel to the bottom of the pot (you need to put something between the jars and heat source).

Place four pint jars in the pot, put a lid on it and place it over high heat. You'll want this pot to reach a boil sometime before the jam is finished cooking, so that the jars are hot when it comes time to pour the jam in. You never want to pour hot jam into cold jars; it can lead to immediate breakage and wasted jam.

Put three inches of water into a small pot and put the lids to the canning jars in it. Make sure you always can with new lids. Once lids have been used, they lose their ability to seal well, which can lead to potential spoilage down the line. Place this pot over a very low flame; you only want it to reach a mere simmer.

With all that done, it’s time to make the jam. Make sure to use a six or more quart, non-reactive pot. Six quarts allows your jam plenty of room to boil and gives you the peace of mind that you’re not going to have molten jam all over your stovetop (the jam will bubble madly). Non-reactive means stainless steel, enameled cast iron or non-stick. Never use bare cast iron or aluminum pots when canning, as they can leach a metallic taste into your jam.

Once the jam is finished cooking, fish the jars out of the canning pot and carefully pour the jam into the jars. When they are all full, make sure to wipe any drips off the rim of the jars before applying the rings. If one of your jars doesn’t get filled all the way, let it cool on the countertop and put it the refrigerator for immediate use. You never want to process half-full jars, as they will float in the canning pot and that can lead to breakage.

Filled jars get carefully lowered into the canning pot and are processed for 10 minutes. Start your timer when the water has returned to a full boil. When the time is up, remove the jars from the canner and place them on a folded towel or wooden cutting board to cool. It’s best not to put them directly on your countertop, particularly if yours is made from granite, marble or some other material that retains a chill.

Once your jars have cooled, it’s important to test your seals to ensure that the jam is now shelf stable. The best way to do this is remove the ring, grip the edges of the lid and gently lift the jar an inch or so off the counter. A well-sealed lid should hold firm and fast. Sealed jam can be stored in a cool, dark place for up to one year. You can also eat it immediately. It's up to you.

Blueberry Jam
Makes 3 1/2 – 4 pints
6 cups of smashed blueberries (4-5 pints whole berries)
4 cups sugar
1 lemon, zested and juiced
2 teaspoons cinnamon
1/2 teaspoon grated nutmeg
3 ounces liquid pectin (that’s the contents of one envelope)

Prepare canning pot, 4 pint jars and lids as described above.

Combine smashed blueberries and sugar to a 6-quart, non-reactive pot. Off the heat, stir to combine so that the sugar can begin to dissolve.

Place pot on burner and bring to a boil. Once it is bubbling nicely, add cinnamon, nutmeg, lemon zest and juice and let jam continue to cook for 15-25 minutes, stirring regularly. It should become very glossy and look like molten sugar. Add pectin and bring back to a rolling boil. Let the jam boil vigorously for an additional 3-4 minutes.

Remove jam from heat. Fill jars, wipe rims and apply lids and rings. Lower into the canning pot. Process in the boiling water bath for 10 minutes. When time is up, remove from water and cool. When the jars are cooled, check the seals. Store up to one year in a cool, dark place.

Next Up

Water Bath Canning for Jams and Pickles

Most fruit preserves and pickles are sufficiently high in acid to be canned via a method called water bath canning, where jars are submerged in boiling water for a prescribed amount of time. This destroys any pathogens in the food, and creates a seal, thereby rendering the jars shelf-stable.