Blueberry jam is a classic preserve that captures the bright, sweet-tart flavour of summer berries in a jar. Making your own jam at home is surprisingly simple, and the result is a delicious, versatile spread that tastes worlds better than shop-bought. This traditional UK-style blueberry jam uses just three main ingredients and no added pectin, making it perfect for toast, scones, or even as a filling for cakes and pastries.
Ingredients
- 1 kg fresh or frozen blueberries
- 800 g granulated sugar
- Juice of 1 large lemon (about 3 tbsp)
- Optional: 1 tsp unsalted butter (to reduce foaming)
Instructions
- Prepare your jars. Wash 3-4 340g jam jars and their lids in hot, soapy water. Rinse well and dry. Sterilise by placing them (and lids) on a baking tray in a preheated oven at 140°C (120°C fan) for 15 minutes. Leave jars in the oven until ready to fill.
- Combine the fruit and lemon juice. Place the blueberries and lemon juice in a large, heavy-based saucepan or preserving pan. If using frozen berries, there’s no need to thaw first.
- Crush the berries. Gently mash about half the blueberries with a potato masher or fork to release some juice, leaving the rest whole for texture.
- Heat gently. Stir over low heat until the blueberries start to release more juices and soften, about 5-8 minutes.
- Add the sugar. Pour in the sugar and stir until fully dissolved. Do not let the mixture boil until all the sugar has dissolved (check by rubbing a little between your fingers; if it feels gritty, keep stirring).
- Bring to a boil. Increase the heat and bring the mixture to a rolling boil. If using, add the butter now to help reduce foaming.
- Boil rapidly. Boil hard for 10-15 minutes, stirring often and skimming off any foam. Use a sugar thermometer if you have one; the setting point for jam is 105°C. If you don’t have a thermometer, use the wrinkle test (see tips below).
- Test for setting point. Place a small plate in the freezer before you start. Once the jam has boiled for 10 minutes, spoon a little onto the cold plate and let it sit for 1 minute. Push gently with your finger—if the surface wrinkles, the jam is ready. If not, boil for another 2-3 minutes and test again.
- Remove from heat. Once the jam has reached setting point, remove from the heat. Let it sit for 5 minutes to allow the fruit to distribute evenly.
- Fill the jars. Carefully ladle the hot jam into the sterilised jars, using a jam funnel if you have one. Wipe the rims clean, seal with the lids while hot, and turn jars upside down for 2 minutes to help create a vacuum seal (optional but common in the UK).
- Cool and label. Allow jars to cool completely, then label with the date. Store in a cool, dark place.
Tips
- Substitutions: You can use a mix of blueberries and other berries (such as blackberries or raspberries) for a unique flavour. Frozen blueberries work just as well as fresh.
- Testing for set: The wrinkle test is a reliable method if you don’t have a sugar thermometer. Always chill the plate well first.
- Storage: Once opened, keep jam in the fridge and use within 4 weeks. Unopened jars will keep in a cool, dark cupboard for at least 12 months.
- Common mistakes: Boiling the jam before the sugar fully dissolves can cause it to crystallise. Always dissolve sugar completely before increasing heat.
Serving Suggestions
- Spread generously on toasted sourdough or crusty bread for a simple breakfast.
- Dollop onto warm scones with clotted cream for a classic cream tea.
- Swirl through plain Greek yoghurt or porridge for a fruity burst.
- Use as a filling for Victoria sponge cakes, Swiss rolls, or jam tarts.
- Serve alongside cheese boards—blueberry jam pairs wonderfully with creamy brie or tangy goat’s cheese.
Variations
- Lemon & Thyme Blueberry Jam: Add the zest of 1 lemon and a few sprigs of fresh thyme during boiling. Remove thyme before jarring.
- Blueberry & Vanilla Jam: Stir in the seeds of 1 vanilla pod or 1 tsp vanilla extract just before filling the jars for a fragrant twist.
- Mixed Berry Jam: Replace up to half the blueberries with raspberries or blackberries for a more complex flavour and deeper colour.
- Lower Sugar Version: You can reduce the sugar to 600g for a tangier, less sweet jam, though it may be slightly softer set and will not keep quite as long.
Storage and Reheating
Properly sterilised and sealed jars of blueberry jam will keep for up to 12 months in a cool, dark cupboard. Once opened, store in the refrigerator and use within 4 weeks for best quality. If your jam becomes too firm after storage, you can gently warm a small amount in the microwave (10-15 seconds) or in a saucepan over low heat to loosen it before serving. Do not attempt to re-can or reprocess opened jam, as this can compromise safety.
Frequently Asked Questions
- Do I need to use pectin for blueberry jam?
Blueberries are naturally low in pectin, but the addition of lemon juice helps the jam set without the need for commercial pectin. Using the correct ratio of fruit to sugar and boiling to the right temperature ensures a good set. If you prefer a firmer set, you can add a sachet of liquid pectin according to the manufacturer’s instructions, but it’s not necessary for this recipe. - Can I use frozen blueberries?
Yes, frozen blueberries work perfectly in this recipe and require no extra preparation. Simply add them straight to the pan; the cooking time may be a minute or two longer as they thaw, but the result is just as delicious as with fresh berries. - My jam didn’t set—what can I do?
If your jam is too runny after cooling, you can re-boil it. Pour the jam back into a clean pan, bring it back to a rolling boil, and cook for another 2-3 minutes, then test again for setting point. Always use the wrinkle test or a sugar thermometer for best results. If you still struggle, consider adding a little commercial pectin next time. - How do I avoid crystallised jam?
Crystallisation usually occurs if the sugar isn’t fully dissolved before boiling. Always stir over low heat until the mixture is completely smooth before increasing the heat. Using granulated sugar (not caster or icing) also helps prevent this issue. - Can I reduce the sugar in this recipe?
You can reduce the sugar slightly, but keep in mind that sugar acts as a preservative as well as a sweetener. Lower sugar jams may set a bit softer and have a shorter shelf life—refrigerate and use within 2-3 weeks once opened if you use less sugar. - Is it safe to can blueberry jam with a water bath?
Traditional UK jam recipes do not require water bath canning if the jam is poured hot into sterilised jars and sealed immediately. However, if you want extra security, you can process the filled jars in a boiling water bath for 10 minutes. Always ensure jars, lids, and utensils are scrupulously clean and sterilised to prevent spoilage.