Blueberry Jam Recipe
A full rolling boil with added pectin sets blueberry jam reliably within minutes, since blueberries alone are naturally low in pectin and would take much longer to thicken without it; a hit of lemon juice balances the berries' sweetness and helps the pectin gel properly.
- Prep
- 15 min
- Cook
- 20 min
- Total
- 40 min
- Servings
- 96
Ingredients
- 4 cups fresh or thawed frozen blueberries, crushed
- 5 cups granulated sugar
- 1/4 cup fresh lemon juice
- 1 box (1.75 oz) powdered fruit pectin
Nutrition per serving
- Calories
- 46
- Protein
- 0g
- Carbs
- 12g
- Fat
- 0g
Based on the recipe as written, one serving. Recalculates if you swap an ingredient above. An estimate only, exact values depend on the specific ingredients used.
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Instructions
- 1Rinse the blueberries and crush them in a large, wide pot using a potato masher, leaving some berries partially whole for texture.
- 2Stir in the lemon juice and pectin. Bring the mixture to a full rolling boil over high heat, stirring constantly so the bottom doesn't scorch.
- 3Add all the sugar at once, return the mixture to a full rolling boil that can't be stirred down, and boil hard for exactly 1 minute, stirring the whole time.
- 4Remove the pot from heat and skim off any foam that has formed on top with a metal spoon.
- 5Ladle the hot jam into sterilized half-pint canning jars, leaving 1/4 inch of headspace at the top of each jar.
- 6Wipe the jar rims clean with a damp cloth, then apply lids and rings until fingertip-tight.
- 7Process the filled jars in a boiling water bath for 10 minutes, then remove them carefully and let them cool undisturbed on a towel for 24 hours.
- 8Check that each lid has sealed (it should be concave and not flex when pressed) before moving jars to storage.
Tips & variations
- Frozen blueberries work as well as fresh; thaw them fully and drain off the excess juice before crushing, or the jam will need extra boiling time to thicken.
- Swap the lemon juice for lime juice for a slightly sharper, brighter flavor against the blueberries.
- Drop a cinnamon stick or split vanilla bean into the pot while boiling, then fish it out before jarring, for a warmer background flavor.
- For a softer-set, less sweet jam, use low or no-sugar-needed pectin and cut the sugar back to 2 to 3 cups; follow the ratio on that pectin's package, since it's formulated differently than regular pectin.
Storage & reheating
Properly processed and sealed jars keep in a cool, dark pantry for up to 1 year. Once opened, refrigerate and use within 3 weeks. If skipping the water bath, treat the jam as refrigerator jam: keep it in the fridge up to 3 weeks or freeze in freezer-safe containers, leaving 1/2 inch of headspace, for up to 1 year.
Tips from the Tulo kitchen
- Chill a small plate in the freezer before cooking. To test the set, drop a small spoonful of hot jam onto the cold plate and push it with a finger; if the surface wrinkles, it's ready.
- Warming the sugar slightly in a low oven before adding it to the pot helps the mixture return to a boil faster and shortens the hard-boil time.
FAQ
Do I need to use pectin for blueberry jam?
No, but blueberries are naturally low in pectin, so a no-added-pectin version needs a much longer boil to reduce and thicken, and it will set softer and more syrupy than a pectin-set jam.
Why did my blueberry jam turn out runny?
The most common cause is not reaching a true rolling boil (one that keeps bubbling even while stirred) for the full minute after adding the sugar, or using underripe berries with more natural acid and less sugar than the recipe assumes.
Can I use frozen blueberries instead of fresh?
Yes. Thaw them completely and drain off the liquid that collects, since extra water in the pot dilutes the sugar and pectin ratio and slows setting.
How can I tell if the jars sealed correctly?
Once the jars have cooled for 24 hours, press the center of each lid; a properly sealed lid stays concave and doesn't pop or flex. Any jar that didn't seal should go straight into the refrigerator and be used within a few weeks.