Low Sugar Raspberry Jam
If you’re looking for a way to capture the pure flavour of raspberries without tipping a truckload of sugar into the mix, my low sugar raspberry jam recipe is the answer. If you want a jam that doesn’t rely on sugar to behave itself, you need low methoxyl pectin (LM), or low methyl ester pectin. LM pectin sets through a reaction with calcium and acid—typically lemon juice—rather than sugar.
Equipment
- 2 x 500ml or 4 x 250ml preserving jars and lids (optional)
- Freezer containers with lids or freezer bags (if freezing)
- 4-5 litre heavy bottomed soup or pasta pot
- large ladle
- wide mouth jam funnel or large pouring jug
- potato masher
- kitchen timer
- If processing jam for longer shelf life:
- Large deep pot with lid (large enough to hold jars covered with boiling water)
- Round cake rack (optional)
- jar lifter or jar tongs
Ingredients
- 1 kg frozen raspberries (defrosted)
- 400 g white granulated sugar
- 2 teaspoons low methoxyl pectin
- 2 tablespoons fresh squeezed lemon juice
- 1 teaspoon butter (optional)
2 teaspoons calcium water
- 125 ml boiled and cooled water
- ½ teaspoon calcium powder
Instructions
- Defrost the frozen raspberries overnight in the fridge.
- Assemble equipment and ingredients.
- Sterilise the preserving jars and lids if using jars (see notes).
- If you plan to process the jars of jam, get the pot of boiling water going.
Make calcium water
- Measure 125ml water that has been boiled and cooled into a clean container with a lid.
- Add ½ teaspoon of calcium powder.
- Shake well.
- Juice the lemon and set aside the lemon juice.
Divide sugar into two bowls and mix in pectin
- 100g (sugar No1)
- 300g (sugar No2)
- Stir 2 teaspoons of low methoxyl pectin into sugar No1 and mix well to distribute the pectin.
Raspberry jam
- Place the defrosted raspberries in a 4-5 litre pot over medium high heat.
- As the berries come to a boil, crush the berries with a potato masher, leaving no lumps or whole berries.
- Once boiling and the raspberry juice has started to release, turn the temperature to high.
- Gradually add sugar No1 stirring well.
- Preset a timer for 90 seconds.
- Then add two teaspoons of calcium water and 2 tablespoons of lemon juice and stir through well.
- Keep stirring as you add sugar No2.
- Bring the raspberry jam to a rolling boil over high heat.
- Start the timer and keep stirring. The jam will thicken and turn a glossy bright red. There should be no sign of any sugar granules.
- Take the pan off the stove after 90 seconds of a full rolling boil.
- Skim off any foam that collects on top of the jam with a dessert spoon. Alternatively, add a teaspoon of butter and stir to disperse the foam.
- Ladle the hot jam into the prepared sterilised jars or containers, leaving about 5mm to 10mm of headspace at the top.
- Wipe the rims clean with a damp cloth.
- Tighten the lid firmly until just sealed.
Storage methods
- To process the jars of jam, see recipe notes.
- If you are planning to consume the jam within 2 weeks, leave the hot bottles of jam on a tea towel on the kitchen bench to cool. Then refrigerate and consume it within 2 weeks.
To freeze the jam
- Use sealed plastic containers or freezer bags.
- When using freezer bags, cool the jam in the pot until it’s just warm.
- Stand the freezer bag up in a large drink cup, draping the edge of the bag over the rim of the cup, Spoon the jam in.
- Carefully seal the bag, letting out as much air as possible as you go. Lie the bags flat on a rimmed baking sheet before placing it in the freezer.
- Once frozen the frozen the raspberry jam filled bags can be stacked in the freezer.
Just before you cook with abandon…
Why use frozen raspberries? In this case fresh is not best. There’s a good reason for using frozen berries in your homemade raspberry jam. The freezing causes the cells of the berries to rupture, allowing the juice to be released and softening the berry. This means that it will take less cooking time to break down the fruit, thereby preserving its fresh taste in the final product.
Can I use bottled lemon juice? Bottled lemon juice is absolutely fine. And, many recipes recommend using bottled juice as the lemon juice helps maintain the right level of acidity and bottled juice will have a consistent Ph level while the Ph level of fresh lemon juice can vary.
What’s low methoxyl pectin? Most raspberry jam recipes lean heavily on sugar, not just for sweetness but to help the jam set and preserve. That’s because they use high methoxyl (HM) pectin, also known as high methyl ester pectin—the same type you’ll find in supermarket "jam sugar." Without enough sugar, HM pectin simply won’t work.
If you want a jam that doesn’t rely on sugar to behave itself, you need low methoxyl (LM) pectin, or low methyl ester pectin. LM pectin sets through a reaction with calcium and acid—typically lemon juice—rather than sugar. It’s the key to making a low carb raspberry jam, or even a completely sugar-free jam, without compromising on texture or structure.
All pectins, whether HM or LM, are naturally plant-derived and vegan.
Unlike HM pectin, LM pectin doesn’t require a high heat to set. It’s set point varies between 50°C and 70°C. LM pectin sets because of the addition of calcium not by reaching a certain temperature. So, you only need to boil the jam enough to the point the berries are cooked and broken down and all the sugar has dissolved.
How do I make calcium water? Low methoxyl pectin is sold with a packet of calcium powder. There are instructions on the package about how to prepare the calcium water. I use boiled and cooled water in a clean plastic sealed container or glass jar with a lid. Measure 125ml of water into the container and add ½ teaspoon of calcium powder. Shake well. Also, remember to shake the container well, just before adding the calcium water to the jam.
Exactly how low sugar can I go? The low methoxyl pectin method of making low carb raspberry jam leaves it up to you to decide how much sugar you wish to add.
The recipe does need some sugar (or granulated sugar substitute like xylitol) so that the pectin can be evenly distributed through the fruit and avoid clumping.
Traditional jams call for a 1:1 ratio of fruit to sugar. In this low sugar raspberry jam recipe, I’ve adopted a 1:0.4 ratio of fruit to sugar (1kg raspberries and 400g sugar). I think this ratio brings out the fresh taste of raspberries while balancing out the tartness of the berries.
Can I swap out the white sugar? You can use other sugars such as coconut sugar, honey, maple syrup, raw sugar, etc. But you will need to experiment with the volumes as they all have their own level of sweetness and much will depend on your palate and what level of sweetness you’re used to.
You can also use sugar substitutes and I have had an OK result with xylitol. But xylitol does leave an aftertaste in the jam so I have chosen to focus on lowering the sugar and not swapping in a sugar substitute.
What is a rolling boil? A ‘rolling boil’ is a technical term when you’re making jam! You’ve achieved a rolling boil at the point when the jam keeps boiling even though you’re stirring it. You want the heat on high and it the jam needs to stay at a full rolling boil for 90 seconds—that’s all.
How long will low sugar raspberry jam last? The shelf life of your jam will depend on the method of storage you choose and how much effort you want to go to. If you plan on using your low sugar raspberry jam within 2 weeks, you just need to ladle it into clean, sealable containers and store it in the fridge. This method is fine if you’re planning to use up in some baking you have planned.
But if you’re not going to get through 1 litre in 2 weeks, it’s best you use the freezer jam method or use pre-sterilised jars and process them using a boiling water bath. This last step will ensure your jam stays safe, shelf-stable, and delicious for months.
Properly processed and sealed jam jars can last up to a year. In my Queensland home in the subtropics, I can never find a room where the temperature is consistently cool. To be sure, I still refrigerate my processed jars of jam. They’re usually fighting it out with the beer and wine for space in our extra fridge!
Boiling water bath processing method
1. Assemble the equipment
Bring water to boil in large, deep pot with a lid. The pot needs to be large enough to hold the jars and enough boiling water to cover the jars by at least 3cm once they’re submerged. Find a rack for the bottom of the pot (or a folded tea towel) to prevent the jars from rattling and bumping each other. You can use a cake rack. I use a stainless-steel steamer insert from a rice cooker.
Fill the pot with enough water to cover the jars by at least 2.5 cm (1 inch) once they’re submerged. Cover and bring the water to a boil before you start your jam, keep it simmering. Bring it to a full rolling boil as you finish the jam.
Have a clean tea towel on the kitchen bench ready for the finished jars.
Keep the kettle boiled in case you need to top up the pot of boiling water.
2. Process the jars
Lower the jars filled with raspberry jam into the simmering water, using a jar lifter or jar tongs. Make sure they are fully submerged and that the water is back to a rolling boil once all jars are in. Process for 5 minutes for 250ml jars and 10 minutes for 500ml jars.
The processing time may need to be adjusted for altitude as the temperature at which water boils changes with altitude. I live at sea level and I am not a scientist! May I suggest Googling this question if needed?
3. Cool jars and check seals
Use the jar tongs to lift the jars out and carefully set them upright on the clean tea towel. Leave them undisturbed for 12–24 hours. As they cool, you should hear the lids ‘pop,’ indicating the lid has sealed. After cooling, check the seals by pressing the centre of each lid—it should not flex up and down. Any jars that haven't sealed properly should be refrigerated and eaten first.
4. Label and store
Once sealed, label and the date jars of low sugar raspberry jam. Store them in a cool, dark place.