preserve · Preserve

How to Make Blueberry Jam

Blueberry jam needs just three ingredients: blueberries, sugar, and lemon juice. Cook them together until the berries break down and the mixture thickens enough to coat a spoon. The whole process takes about 20 minutes of active cooking, and you'll know it's ready when a small amount gels on a cold plate.

Total time: 35 min
Hands-on: 35 min
Difficulty: Easy

Ingredients

2 pounds fresh blueberries
1 cup granulated sugar
2 tablespoons fresh lemon juice

Step by step

Prepare your blueberries. Rinse 2 pounds of fresh blueberries and remove any stems or damaged berries. Put a small plate in the freezer—you'll need this cold plate to test when your jam is ready.
Combine ingredients in a heavy-bottomed pot. Add the blueberries, 1 cup of granulated sugar, and 2 tablespoons of fresh lemon juice to a wide, heavy-bottomed saucepan. The wide surface helps water evaporate faster.
Macerate the fruit. Stir everything together and let it sit for 10 minutes. The sugar will start pulling juice from the berries, creating a syrup at the bottom of the pan.
Start cooking over medium-high heat. Bring the mixture to a rolling boil, stirring frequently. The berries will start to burst and release more juice. This takes about 5 minutes.
Reduce heat and continue cooking. Lower the heat to medium and keep cooking, stirring regularly. The jam will bubble vigorously and start to thicken. Mash some berries against the side of the pan with your spoon, but leave some whole for texture.
Test for doneness. After 15-20 minutes, test your jam by dropping a small amount on the cold plate from the freezer. If it holds its shape and doesn't run when you tilt the plate, it's ready. If it's still too liquid, cook for a few more minutes and test again.
Finish and store. Remove from heat and let cool for 5 minutes. Pour into clean jars, leaving a quarter-inch of headspace. The jam will continue to thicken as it cools.

Tips & troubleshooting

Use a potato masher instead of a spoon to control how chunky or smooth you want your jam
Don't double the recipe—larger batches take too long to cook and the fruit can get mushy
Frozen blueberries work perfectly and often break down faster than fresh ones
If your jam is too thick after cooling, stir in a tablespoon of hot water
Store in the refrigerator for up to 3 weeks or process in a water bath for longer storage
Skim off any foam that forms during cooking for a clearer-looking jam

Variations

Lower Sugar Jam. Reduce sugar to 3/4 cup for a more tart jam that highlights the berry flavor. Add an extra tablespoon of lemon juice to help it set.
Spiced Blueberry Jam. Add a cinnamon stick, 3 whole cloves, or a strip of lemon zest during cooking. Remove the whole spices before jarring.
Mixed Berry Version. Replace half the blueberries with blackberries or raspberries for a more complex flavor. Keep the same sugar and lemon proportions.
Vanilla Blueberry Jam. Scrape the seeds from half a vanilla bean into the pot, or add 1 teaspoon vanilla extract after cooking is complete.

Questions

Why didn't my jam set properly?: Usually this means it needed more cooking time. Blueberries have natural pectin, but it needs time and heat to activate. Cook longer until the plate test shows it gels. Very ripe berries have less pectin, so add an extra tablespoon of lemon juice if your berries are very sweet.
Can I make jam without added sugar?: Sugar isn't just for sweetness—it helps the jam set and preserves it. You can reduce the sugar, but going below half a cup per two pounds of berries makes setting difficult. The jam will also have a shorter refrigerator life.
How do I know when the jam is thick enough?: The cold plate test is most reliable. A properly set jam will wrinkle when you push it with your finger on the cold plate. You can also watch for the jam to coat your spoon thickly, or listen—the bubbling sound changes when most of the water has cooked off.
What's the white foam that forms while cooking?: That's just proteins and air bubbles from the fruit. It's harmless but removing it makes your jam look cleaner. Skim it off with a spoon partway through cooking.
Can I use this jam for canning?: Yes, but you'll need to process the filled jars in a boiling water bath for 10 minutes to make them shelf-stable. Make sure your jars and lids are properly sterilized first.