If you’ve got more blackberries than you know what to do with, this jam recipe is a good way to use them up (especially if you’ve been growing them on your own blackberry trellis).
It’s simple and gives you jars of thick, sweet jam you can enjoy for months.
The slow overnight soak keeps the fruit from turning mushy, and the lemon helps the jam set just right. You can make the full batch or cut it in half if you don’t need quite so much.
In this article, you’ll find everything from the ingredients and equipment you’ll need, to step-by-step instructions, storage tips, and answers to common questions so your jam turns out right every time.
Ingredients
For a full batch (about 8 jars), you’ll need:
- 1.8 kg blackberries – ripe and rinsed clean.
- 1.5 kg jam sugar – this sugar already has pectin in it, which helps the jam set.
- Juice and pips of 1 lemon – the juice adds a bit of brightness, and the pips add extra pectin.
- A fingertip-sized knob of butter (optional) – helps get rid of any foam on top of the jam.
If you don’t want to make the full amount, you can easily halve these quantities and still get a few jars of jam.
Essential Equipment
Having the right tools makes the job easier and helps your jam turn out right.
- Very large bowl – for soaking the blackberries and sugar overnight.
- Small saucer – used for testing if the jam has set (you’ll pop this in the freezer).
- Preserving pan or a large, wide-based pan – a wide pan helps the jam cook faster and more evenly.
- Tea-leaf strainer or a piece of muslin – to hold the lemon pips so they don’t end up in the jam but still release pectin.
- About 8 jam jars – clean and sterilised, ready to fill.
- 8 waxed discs – these sit on top of the jam to help keep it fresh.
- 8 jar lids or cellophane circles with rubber bands – to seal the jars once they’re filled.
Preparation Timeline
Making a jam does take a bit of planning. Here’s how much time you’ll want to set aside:
Prep time: About 20 minutes – this includes rinsing the berries, layering them with sugar, and getting things ready.
Overnight soak: Leave the berries and sugar covered at room temperature overnight. This helps the sugar dissolve slowly and keeps the fruit from overcooking.
Cooking time: Around 40 minutes – from heating the mixture to testing and reaching the setting point.
It’s best to start this recipe in the evening so the fruit can soak overnight and you can cook the jam the next morning.
Step-by-Step Method
Making blackberry jam is a simple process, but it works best if you follow the steps in order.
From soaking the berries to sealing the jars, each stage plays a part in getting a thick, flavorful jam that lasts for months.
Step 1: Let the Blackberries Soak Overnight
In a very large bowl, layer the blackberries and jam sugar. Cover the bowl and leave it at room temperature overnight.
This slow soak helps the sugar begin to dissolve and keeps the berries from breaking down too much when you cook them the next day.
Step 2: Pre-Cooking Setup
The next morning, place a small saucer in the freezer – you’ll use this later to check if the jam is ready.
Tip the blackberry and sugar mixture into your preserving pan, making sure to scrape in every bit of juice and any sugar left in the bowl. Stir in the lemon juice.
Gather all the lemon pips, tuck them into a tea-leaf strainer or wrap them in muslin, and drop that into the pan. The pips are full of pectin, which will help the jam set.
Step 3: Cooking and Reaching the Setting Point
Warm the mixture gently over a low heat, stirring often until all the sugar has dissolved. Once there are no sugar crystals left, bring the mixture to a boil and let it simmer for about five minutes.
Turn off the heat and test for setting by spooning a little jam onto the chilled saucer from the freezer.
Let it cool for a minute, then push it gently with your finger – if the surface wrinkles, the jam is ready.
If it’s still runny, put the pan back on the heat for another two to three minutes, then test again.
Repeat this process until you get that wrinkle.
Step 4: Finishing the Jam
Once the jam has reached the setting point, skim off any foam that has gathered on the surface.
If you like, stir in a small knob of butter, which can help clear away any last bits of foam. Let the jam sit for about fifteen minutes before jarring.
This rest allows the fruit to settle evenly throughout the jam instead of floating to the top of the jars.
Step 5: Jarring the Jam
Make sure your jars are sterilised and still warm, as a sudden change in temperature can cause them to crack.
Ladle the jam into the jars while it’s still hot, place a wax disc on top of each, and seal them with a lid or cover them with cellophane and secure with a rubber band.
Keeping Your Jam Fresh
Once your jars are sealed, they need to be stored somewhere cool and dark. A pantry, cupboard, or any spot away from direct sunlight will work well.
The key is to keep them in a place where the temperature stays fairly steady, as heat or sudden changes can shorten the shelf life.
When sealed properly using water bath canning, blackberry jam will keep its flavor and texture for up to a year.
If you’ve just made the jam and aren’t sure the seal took, don’t risk storing it on the shelf – keep those jars in the fridge and use them within a month.
Once you open a jar, move it to the fridge straight away. Try to finish it within three to four weeks for the best taste and to avoid mold.
Always use a clean, dry spoon when serving, as even a small bit of leftover butter or crumbs can cause the jam to spoil faster.
If you live in a hot or humid climate, you might want to keep all your jars in the fridge from the start, just to be safe – you can find more ideas in our canned food storage tips.
Common Mistakes (and How to Fix Them!)
Even with a simple recipe, jam-making can have its hiccups. Here’s what can go wrong and how to set it right.
Jam turns out too runny
This usually means it didn’t reach the setting point. It can happen if the fruit didn’t have enough pectin or if it wasn’t boiled long enough.
You can fix it by returning the jam to the pan, adding a little extra lemon juice, and boiling in short bursts until it passes the wrinkle test on a chilled saucer.
Jam ends up too thick
Overcooking is the main cause. If the jam is very thick but still spreadable, it’s fine to eat. For a softer set next time, check the saucer test earlier and remove it from the heat as soon as it wrinkles.
Sugar crystals in the jam
This happens when the sugar wasn’t fully dissolved before boiling. Make sure to stir over a low heat until every grain of sugar is gone before turning up the heat.
Avoid stirring the jam once it’s boiling, as this can also cause crystals to form.
Foam on top of the jam
Foam isn’t harmful, but it can make the surface look cloudy. Skim it off with a spoon, or stir in a small knob of butter at the end of cooking to help it dissolve.
Fruit floating to the top of the jars
If the fruit rises after jarring, it means it wasn’t given time to settle. Let the jam rest for about fifteen minutes after cooking before filling your jars so the fruit spreads evenly.
Make the Most of Your Blackberries
Turning fresh blackberries into jam is one of the easiest ways to enjoy them all year round.
With just a few ingredients and a bit of patience, you can fill your pantry with jars of rich, flavorful jam that’s perfect for toast, baking, or gifting.
Follow the soaking, cooking, and sealing steps closely, and you’ll have a batch that keeps well and tastes just as good months from now as it does the day you make it.
If you’ve tried this recipe or have your own jam-making tricks, share them in the comments below – your tips might help someone else’s batch turn out even better!
FAQs
Can I use frozen blackberries instead of fresh?
Yes, frozen blackberries work well for jam. Thaw them first, then include all the juice they release in the pan so you don’t lose flavor.
What’s the best way to sterilise jars?
Wash the jars in hot soapy water, rinse well, and place them in a warm oven (about 140°C / 285°F) for 15–20 minutes. Keep them warm until you’re ready to fill them.
Can I make this without jam sugar?
You can use regular sugar, but you’ll need to add extra pectin or cook the jam longer to get it to set. The texture might be softer.
How do I make the jam less sweet?
Reduce the sugar slightly, but be careful – sugar helps the jam set and keeps it from spoiling. If you cut too much, the jam might be runny or have a shorter shelf life.
Can I mix in other fruits for variety?
Yes, you can combine blackberries with raspberries, blueberries, or even apples. Just keep the total fruit weight the same as the recipe and adjust the sugar if needed.