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Strawberry Rhubarb Jam {Low-Sugar}

Homemade Strawberry Rhubarb Jam is a delicious spread for toast, yogurt, or dessert recipes. Thanks to the low-sugar recipe, this jam tastes fresh and bright, just like real fruit.

Multiple jars of strawberry rhubarb jam on a white board and a biscuit

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That magical few weeks when strawberries and rhubarb are ripe at the same time just beg for baking and jam making. Once you’ve already made at least one gluten-free strawberry rhubarb crisp, it’s time to make jam!

STRAWBERRY Rhubarb JAM EQUIPMENT

  • Jars! Canning jars only (don’t use leftover mayo, jam, or pasta sauce jars from the store). I recommend 8 oz jam jars, or pints if your family goes through jam quickly.
  • Clean, never before used canning lids
  • Canning rings
  • Pomona’s Pectin (or another low-sugar pectin brand)
  • Water bath canner or deep stockpot with a jar rack. 
  • Large saucepan. I adore my dutch oven for so many reasons, and jam season is another one of those reasons! Having a wide pot with high sides is best for making jam as it allows the jam to process at a rolling boil without slopping over the sides.
  • Ladle
  • Funnel
  • Jar lifter
  • Clean washcloths and towels
  • Medium mixing bowl
  • Something to stir with (I love this thingy)
  • Knife and cutting board
  • Comfy shoes

Check out this Canning Supplies and Equipment List for a detailed explanation of all the supplies and brands I recommend, as well as ideas on where to find items for free/cheap.

HOW TO MAKE STRAWBERRY Rhubarb JAM

*A detailed and printable recipe is available at the bottom of this post

CANNING PREP

Prepare your water bath canner by filling it halfway with water, and setting it on the stove. Turn the burner to high. Once it reaches a boil, reduce it to simmer. You want to keep the water hot so that everything is ready when the jam is.

Wash and clean your jars. You’ll want to keep them warm to avoid having them crack when placed in the canner. You can fill them with hot water, or place them on a tray in the oven at 170F.

Wash your lids and set them aside in a clean place. You no longer need to simmer lids in water to keep them sterile. Woot!

Making the jam

Rinse the strawberries. Remove the tops, cut in half (or quarters for large berries), and place in a bowl. Gently mash with a potato masher or pastry cutter until it yields 2.5 cups of mashed berries.

You can also “cheat” and start with Strawberry Puree or Frozen Strawberries in Syrup if you already have some on hand.

Add the rhubarb to a heavy-bottomed saucepan with 1/2 cup of water. Cook on medium heat, stirring often until the rhubarb softens. You’ll need about 4 cups of fresh sliced rhubarb to yield 1.5 cups of cooked rhubarb. Stir in the mashed strawberries and continue to cook the mixture until the fruits are combined.

In a small bowl, combine 1/2 tsp calcium powder (in the Pomona’s Pectin box) with 1/2 cup cool water to create calcium water.

In a separate bowl, combine sugar and pectin. Set aside. To prevent clumping, Pomona’s must be mixed with your sweetener before being added to the fruit.

Add the lemon juice and calcium water to the pot with the rhubarb and strawberries, stir.  Add the sugar/pectin mixture, and bring to a rolling boil. Stir constantly for 3 minutes, turning down the burner to medium if the jam starts popping. Pro tip: actually set a timer and stir for the full three minutes. The constant stirring prevents the jam from burning, and the cooking time is important to help the jam set.

5 photos showing the process of making rhubarb strawberry jam

Pro tip: a rolling boil means no amount of stirring will stop the bubbling. Use a long spoon or spatula to avoid any jam popping onto your hand. 

At this point, turn the burner under the canner back up to high and get that water boiling again.

Remove the jam pot from heat, and stir gently for 5 more minutes. At the end of the 5 minutes, remove any foam that remains.

Using the funnel and a ladle, add the jam to your prepared jars, leaving 1/4 inch of headspace at the top. Headspace is the amount of room between the top of the food, and the rim of the jar.

Using a wet clean rag, wipe the rim to make sure there isn’t any sticky jam on there. 

Place a clean lid on the jar and then a canning ring. Tighten the ring to fingertip tight (tight enough that it won’t come off, but not so tight that a normal person couldn’t budge it).

3 photos showing how to can strawberry rhubarb jam

Using canning tongs, add your jars to the boiling water, and put the canner lid on. Pro tip: you must have at least 1 inch of water over the tops of the jars for safe canning. Process (boil) for 10 minutes. 

Remove the canner from heat, and let sit for 5 minutes. Remove the jars and place them on towels on the counter. Make sure you put them someplace where they can be undisturbed for 12-24 hours.

After everything has cooled, check the seal by pushing down on the middle of the lid. If it doesn’t give way, it’s sealed. Label the jars, and store them in a cool dark place for up to a year. If the lid bows a little bit, put that in the fridge and use it within 3 weeks.

Can You Use Frozen Fruit for Jam?

Yes! This jam works great if made with frozen fruit (Related: How to Freeze Strawberries and How to Freeze Rhubarb). You may need to drain any excess juices that are produced during the thawing process.

HOW TO TEST TO SEE IF THE JAM IS SET – SPOON/SHEET TEST

If you want to double or triple-check that your jam will set, try the spoon/sheet test. Stir a metal spoon into the jam and hold it sideways above the pot. If the jam runs off in drips, then keep cooking it. It’s just not ready.

But, if the jam drops start to run together and come off the spoon in a sheet, your jam is done! Yay!

rhubarb strawberry jam on a biscuit

Pro Tips/Recipe Notes

  • If you prefer a tarter jam, use 2.5 cups of cook rhubarb and 1.5 cups of mashed strawberries.
  • You can keep an opened jar in the fridge for a month. Sealed jars are safely stored at room temperature for up to a year.
  • Jam is best when made in small batches. Avoid doubling or tripling the recipe.
  • The mixed calcium water will last for three months in the fridge. Shake well before using it for other recipes like Low-Sugar Strawberry Jam.
  • You can reduce the sugar to 1 cup if desired but you would need to cook the jam down for 8 minutes instead of 3.

MORE GREAT RECIPES LIKE THIS

Strawberry Rhubarb Jam (Low Sugar)

Prep Time20 mins
Cook Time30 mins
Total Time50 mins
Homemade Strawberry Rhubarb Jam is a delicious spread for toast, yogurt, or dessert recipes.

Ingredients

  • 2.5 cups strawberries {mashed}{~4 cups fresh}
  • 1.5 cups cooked rhubarb {~4 cups raw, diced}
  • 1 cup water, divided {plus more for the canner}
  • 2 tbsp bottled lemon juice
  • 3 tbsp Pomona's Pectin
  • 3 tbsp calcium water {from Pomona's Pectin box}
  • 1.5 cups sugar

Instructions

Prep for Canning

  • Prepare water bath canner by filling it halfway with water, and setting it on the stove. Turn the burner to high. Once it reaches a boil, reduce it to simmer. You want to keep the water hot so that everything is ready when the jam is.
  • Wash and clean your jars. Fill with hot water or keep them warm in a clean dishwasher or oven.
  • Wash your lids and set aside in clean place.

Making the Jam

  • Rinse the strawberries. Remove the tops, cut in half or quarters, and place in a large bowl.
  • Gently mash with a potato masher or pastry cutter until it yields 2.5 cups of mashed berries.
  • Add the clean chopped rhubarb to a heavy-bottomed saucepan with 1/2 cup water.
  • Cook on medium heat, stirring often until the rhubarb softens.
  • Stir in the strawberries and continue to cook the mixture until the fruits are well-combined.
  • In a small bowl, combine 1/2 tsp calcium powder from the Poman's Pectin box with 1/2 cup cool water to create calcium water.
  • In a separate bowl, combine 1.5 cups of sugar and 3 tbsp of Pomona's pectin. Set aside.
  • Add 2 tbsp lemon juice and 3 tbsp calcium water to the pot with the rhubarb and strawberries, stir.
  • Add the sugar/pectin mixture, and bring to a gentle rolling boil.
  • Stir constantly for 3 minutes, turning down the burner to medium if the jam starts popping.
  • At this point, turn the burner under the canner back up to high and get that water boiling again.

Canning the Jam

  • Using the funnel and a ladle, add the jam to your prepared jars, leaving 1/4 inch of headspace at the top. Headspace is the amount of room between the top of the food, and the rim of the jar.
  • Using a wet clean rag, wipe the rim to make sure there isn't any sticky jam on there.
  • Place a clean lid on the jar and then a ring. Tighten the ring to fingertip tight.
  • Using canning tongs, add jars to the boiling water, and put the canner lid on. Pro tip: you must have at least 1 inch of water over the tops of the jars for safe canning.
  • Process (boil) for 10 minutes. 
  • Remove the canner from heat, and let sit for 5 minutes.
  • Remove the jars and place them on towels on the counter undisturbed for 12-24 hours.
  • After everything has cooled, check the seal by pushing down on the middle of the lid. If it doesn't give way, it's sealed. If the lid bows a little bit, put that in the fridge and use it within 3 weeks.
  • Label the sealed jars, and store in a cool dark place for up to a year.

Notes

Makes 5, 8 oz jars.
 
Will last for 1 month in the fridge or 12 months sealed and at room temperature.
Nutrition Facts
Strawberry Rhubarb Jam (Low Sugar)
Amount Per Serving (1 tbsp)
Calories 26 Calories from Fat 9
% Daily Value*
Fat 1g2%
Saturated Fat 1g6%
Polyunsaturated Fat 1g
Monounsaturated Fat 1g
Sodium 1mg0%
Potassium 22mg1%
Carbohydrates 7g2%
Fiber 1g4%
Sugar 6g7%
Protein 1g2%
Vitamin A 5IU0%
Vitamin C 5mg6%
Calcium 4mg0%
Iron 1mg6%
* Percent Daily Values are based on a 2000 calorie diet.

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2 comments on “Strawberry Rhubarb Jam {Low-Sugar}”

  1. Sounds delicious. I usually make freezer jam and both your recipe and mine for freezer specify mashing the berries instead of using a food processor. Why?

    • I believe to keep some of the berries intact so the “gel” happens. If you processed them too much, you’d essentially be making really watery jelly that wouldn’t set. I believe in most cases, “real” jelly requires a ton more sugar too.