Canning Strawberry Jam

Canning Strawberry Jam is a delicious, low-sugar, and fresh-tasting spread for toast, yogurt, or dessert recipes. Homemade strawberry jam is an amazing way to preserve the harvest and is a treat for the whole family. 

This low-sugar strawberry jam recipe is exactly how homemade jam should taste – not too sweet and tasting of summer. Unlike traditional strawberry jam, it tastes like fresh berries, not sugar.

This post is long because I have stuffed it full of information, tips, tricks, and hacks I have learned over 20 years of canning. I’m telling you EVERYTHING you need to know to be successful at making homemade strawberry jam in your very own kitchen.

You can always click “jump to recipe” if you’d like, but I highly recommend a read-through at least once to make sure you understand what is going on.

How to Use Pomona’s Universal Pectin

Each box of Pomona’s comes with two little packages; 1) calcium powder 2) and pectin.  

You mix 1/2 tsp of calcium powder with 1/2 cup of water. You won’t use it all for this recipe, but it can be stored in the fridge for 2-3 months.

How to Make and Can Strawberry Jam

*I’ll walk you through it here with some photos and tips, and you’ll also find a printable recipe card at the bottom of the post with exact measurements, etc. You can also click “jump to recipe” to skip down.

Canning Prep

Prepare your water bath canner by filling it with water, and setting it on the stove. Turn the burner to high. Once it reaches a boil, reduce it to simmer. You want to keep the water hot so that everything is ready when the jam is.

Wash and sanitize your jars. You’ll want to keep them warm to avoid having them crack when placed in the canner. You can fill them with hot water, or place them on a tray in the oven at 170˚F.

Wash your lids and set them aside in a clean place. You no longer need to simmer lids in water to keep them sterile. Woot!

Making Strawberry Jam

Rinse the strawberries. Remove the tops, and place in a heavy-bottomed saucepan. You can also “cheat” and start with Strawberry Puree if you already have some on hand.

Heat the fruit over medium heat until the juices start to bubble. If your strawberries are ripe you should not need to add any water to the pot. Just stir often to prevent sticking, and soon the natural juices in the berries will be released. Be patient!

At this point, you can mash the fruit with a potato masher, but I prefer to be lazy and use my immersion blender. Pro tip: blend about 30% of the strawberries, and just gently pulse the others, leaving some chunks. The goal isn’t to puree the fruit completely as that will impact the final texture of the jam.

In a small bowl, combine 1/2 tsp calcium powder with 1/2 cup cool water. <–this comes in the box of low-sugar pectin.

In a separate bowl, combine sugar and pectin. Set aside. To prevent clumping in the fruit, Pomona’s must be mixed with your sweetener before being added to the fruit.

Add the bottled lemon juice and calcium water to the pot with the strawberries, and stir.  Add the sugar/pectin mixture, and bring everything to a rolling boil. Stir the mixture constantly for 3 minutes, turning down the burner to medium if the jam starts popping.

Pro tip: actually set a timer and stir for the full three minutes. The constant stirring prevents the jam from burning, and the cooking time is important to help the jam set.

Pro tip #2: a rolling boil means no amount of stirring will stop the bubbling. Use a long spoon or spatula to avoid any jam popping onto your hand. Dibs on “Jam Hand” as a band name.

At this point, turn the burner under the canner back up to high and get that water boiling again.

Remove the jam pot from the heat, and stir it gently for 5 more minutes. At the end of the 5 minutes, skim off any foam that remains.

Using canning tongs, add your jars to the boiling water, and put the canner lid on. Pro tip: you must have at least 1 inch of water over the tops of the jars for safe canning. Processing times will vary based on altitude. See the chart below.

Remove the canner from heat, remove the lid of the canner, and let the canner sit for 5 minutes. Use canning tongs and remove the jars and place them on towels on the counter. Make sure you put them where they can be undisturbed for 12-24 hours.

After everything has cooled, check the seal by pushing down on the middle of the lid. If it doesn’t give way, it’s sealed. Label the jars, and store in a cool dark place for up to a year. If the lid bows a little bit, put that in the fridge and use it within 3 weeks.

Common Strawberry Jam Issues

Help, my jam didn’t set!

I have found with Pomona’s that every batch has set because it doesn’t depend on sugar to create the gel. If you’re using another brand of pectin, the common reason for the jam not setting is that it wasn’t cooked long enough or the (appalling) amount of sugar called for was adjusted.

Jam must be fully cooled in the jars for 24 hours before it is determined if it has truly set. It will thicken as it cools.

If your jam truly looks liquidy after 24 hours, Pomona’s has an amazing step-by-step guide on their site for troubleshooting and fixing jam issues.

How to test to see if the jam is set – spoon/sheet test

If you want to double or triple-check that your jam will set before canning it, try the spoon/sheet test. Stir a metal spoon into the jam and hold it sideways above the pot. If the jam runs off in drips, then keep cooking it. It’s just not ready.

But, if the jam drops start to run together and come off the spoon in a sheet, your jam is done! Yay!

Help, the Bottom of My Jam Jar is All Juice!

Been there, jammed that.

Once your jam has set, there may be some settling happening in the jar. That’s normal! But sometimes, what the final product looks like is strawberry liquid on the bottom and actual jam on the top. 

This occurs when the strawberries were over crushed/smushed and too much juice was released. If you’re using a potato masher to process the strawberries, do so one layer at a time.