Raspberry freezer jam is a sweet and tart jam that's made on the stovetop and stored in the refrigerator or freezer. This small batch recipe makes two 8-ounce jars.
In a saucepan over medium heat, add raspberries, granulated sugar, lemon juice, and cornstarch. Stir until sugar has dissolved.
Bring to a boil, then reduce heat to medium-low. Simmer for 10-12 minutes, stirring occasionally. Gently mash any large pieces with your spoon as you stir. The mixture should thickly coat the back of a spoon (and will continue to thicken as it cools).
Jam not thickening? Make a slurry of 1 teaspoon of cornstarch and water, then slowly add to your jam while stirring constantly.
Remove from heat and allow to cool slightly in the pan. Transfer to jars and allow to cool completely before adding lids. Store for up to 1 year in freezer, or up to 3 weeks in the refrigerator.
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Notes
If your berries are in-season and very juicy, you may need to add additional cornstarch to thicken the jam to your desired consistency. Make a slurry of cornstarch and water, then slowly add to your jam while stirring constantly.
Test the sweetness of your jam before removing from the heat. This recipe will produce a tart, lightly sweet jam. If you prefer a sweeter jam, add up to double the amount of sugar, or until desired sweetness is achieved. Stir to incorporate, and wait until sugar is dissolved before removing from heat.
If freezing, leave ½" at the top of the jar to allow the jam to expand slightly when freezing.
Freezer jam is NOT shelf stable and needs to be kept in the freezer or refrigerator. Treat your freezer jam like fresh produce, it will go bad after a few weeks in the refrigerator.
16 ounces of raspberries = about 3.5 to 4.5 US cups of raspberries. Measuring raspberries by the cup can be unreliable due to the varying size and shape of the berries you have on hand. I highly recommend measuring your raspberries by weight. Bags of frozen raspberries and raspberries sold in plastic clamshell containers are all labeled by weight.