Jams tend to be pretty sweet, even homemade ones, because extra sugar is necessary for the jam to properly gel. A strawberry rhubarb jam is more balanced thanks to the extra tart rhubarb.
I played around with different ratios of strawberries and rhubarb with the goal to add as much tartness as possible to the jam without going overboard. I settled on using twice as much rhubarb as strawberries, based on their weight.
I also made this jam without pectin. Strawberries and rhubarb are lower in pectin that other fruits, but they still have enough that the jam gels as it is cooked down. If you're looking for other variations of strawberry rhubarb jam, I have a bunch listed at the bottom of the article.
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Recipe
Ingredients
- 2 lbs rhubarb
- 1 lb strawberries about 1.5 pints
- 2 ½ cups sugar
- 3 tablespoon bottled lemon juice
- 1 teaspoon vanilla or almond extract optional
Instructions
- Prepare fruit: chop rhubarb into small pieces (¼" in size, roughly). They break down some when cooked, but not completely, so you don't want large pieces. Remove tops of strawberries and cut in half (cut large ones into quarters).
- Cook jam: Combine all ingredients into a pot over medium heat and bring to a boil. Stir as it continues to boil.
- Cook until it reaches 220℉ at sea level. This is the temperature when the jam gels up. It takes me anywhere from 15-40 minutes to reach 220℉ depending on the batch - it depends on how much liquid is in the fruit. The more water in the fruit, the longer it takes. The temperature for gelling is adjusted down for higher elevations: Sea level at 220℉ / 2000 feet at 216℉ / 4000 feet at 212℉ / 6000 feet at 209℉
- Remove from heat and quickly skim off foam. The foam takes up head space in the jar which can cause problems when canning. You want to do it quickly enough than the jam hasn't cooled because you need to pour hot jam into the jars for sterile canning.
- Pour into jars & add to water bath: Pour jam into jars, leaving ¼" of headspace. Wipe the rims clean. Add the rings until they are finger tight. Place in a gently boiling water bath, covered by at least 1 inch of water.Boil for 10 minutes (adjusted for altitude). Turn off heat and let the jars sit in the water bath for 5 additional minutes. Remove jars and cool. Check lids for seals.Altitude adjustments: 0-1000 feet needs no added adjustments, boil for 5 extra minutes up to 3,000 feet, add 10 minutes for up to 6,000 feet, and add 15 minutes for elevations over 6,000 feet.
Notes
Nutrition
Using fresh strawberries & rhubarb
Rhubarb season starts in early spring, with strawberries ripening shorty after. Their overlapping seasonality is one of the main reasons for their popular pairing. Rhubarb adds a tart & tangy flavor to the strawberries, which cuts through the sweet flavors for a balanced jam.
Rhubarb & strawberry ratio
I wanted a tart jam that didn't taste too acidic, but I didn't want it to be mistaken for a regular strawberry jam either. I tested several variations and found that using twice as much rhubarb as strawberries (by weight) yielded the perfect balance.
- Equal parts strawberries & rhubarb: very sweet and couldn't taste the rhubarb
- 1.5 times as much rhubarb: this jam came out slightly tart and pretty tasty
- Twice as much rhubarb as strawberries: perfectly tart with a noticeable rhubarb flavor
Where to find rhubarb
Rhubarb grows best in colder climates where the ground freezes in winter. In those regions, you can find rhubarb at farmers markets and often grocery stores.
In warmer regions, it can be pretty difficult to find fresh rhubarb. Keep tabs on the grocery stores throughout spring and early summer. Whole Foods is a good bet, and there are reports of the big grocery chains selling rhubarb as well.
You can store rhubarb in the fridge for about it week. If it goes limp (like celery sometimes does), that's ok. You can still use it in this jam recipe as long as there are no signs of decay.
Don't eat rhubarb leaves, they are poisonous.
Strawberries: ripe vs under-ripe
Fresh strawberries that are perfectly ripe for the season great in a jam. The more ripe they are, the less pectin, so it might have to boil longer.
Strawberries from the grocery store are often less ripe. If you get bland, under-ripe strawberries, jam is actually a good use for them. They have more pectin, the gelling process will likely be easier. The addition of sugar, lemon juice and rhubarb rescue bland flavored strawberries as well.
Making jam without pectin
Pectin has gelling properties and it's naturally found in fruit. Some fruit has more than others. Apples and cranberries are very high in pectin, whereas strawberries and rhubarb are on the lower end.
Commercial pectin is made from apples and citrus peels that would otherwise go to waste in the food processing chain. Many recipes call for added pectin to ensure the jams set and to reduce cooking time. Recipes that use added pectin often call for more sugar as well, which is necessary to activate the pectin. (There are low-sugar pectin options if you're interested.)
Strawberries and rhubarb do have enough pectin to properly gel on their own, they just need to cook longer. A longer cooking time does affect the flavor - it's hard to describe. I can best explain it by saying that jam with minimal cooking has a flavor truer to the fruit and tastes less 'jammy.'
I still prefer jams without pectin because I think the consistency is better. Jam without pectin has less water in it - so it's a more concentrated fruit spread, closer to a preserve than a jelly. Jam made with pectin has more gelled-water and is closer to a jelly.
That said, it's up to you! If you're looking for a jam with pectin, I have some recipes for you to check out at the bottom of this article.
How to set jam without pectin
If you want to make the jam without added pectin, the National Center for Home Food Preservation lists two different methods for testing the gelling properties.
The first method is to pour a bit of jam on a cold plate and place it in the freezer. If it gels after a few minutes, it's ready to be canned. The second method is to boil the jam until it reaches a specific temperature: 220ºF.
I've found the most reliable method is to cook the jam until it reaches the specified temperature. It's worked well for this strawberry rhubarb jam as well as all of my other ones. It comes out perfectly spreadable - not too thick and not too thin.
The target temperature is adjusted down based on your elevation.
| Altitude (feet) | Target temperature |
|---|---|
| Sea level | 220ºF |
| 1,000 | 218ºF |
| 2,000 | 216ºF |
| 3,000 | 214ºF |
| 4,000 | 212ºF |
| 5,000 | 211ºF |
| 6,000 | 209ºF |
| 7,000 | 207ºF |
| 8,000+ | 205ºF |
Pectin also needs enough acid and sugar to gel, which is why altering recipes changes the jams consistency. The amount of acid should not be altered, as the amount stated is often necessary for safe canning.
Sugar's role in jam
The amount of sugar, however, can be adjusted (with the risk of making jam that doesn't set). Sugar acts as a preservative, but in the case of jams and jellies, it isn't needed for safe canning.
Ball's Book of Canning and Preserving clarifies this even further, saying, "Sugar has preserving properties as it replaces some of the water in fruit, but the amount used in canning is just enough to help delay spoiling once jars are opened." (my emphasis)
Sugar does still act as a preservative in jams and jellies, but for other reasons. As the Ball Book of canning points out, it increases the shelf life of the jam once it's opened and stored in the fridge. Low sugar jams need to be used up much faster once opened.
Second, sugar preserves the texture and color of fruit when canned. Without enough sugar, a strawberry rhubarb jam can lose its rich, bright red color. Over time, it will turn paler and sometimes brownish.
Why skim foam off the jam?
Foam forms when the air inside the fruit escapes during the boiling process. Macerating the strawberries in sugar before making the jam reduces the foam. While unnecessary, you can do it if you want to.
By nature, foam is airy and takes up a lot of space. The reason you skim it off before canning the jam is to control the headspace in the jar. If there's too much headspace, jars might not properly seal and the jam can discolor and develop off flavors during storage.
The best way I've found to skim the foam off the jam is with a small metal spoon - once the pot has been removed from the heat. Foam can continue to form as the jam boils, so it isn't worth removing it until the boiling subsides.
Northwest Edible Life has an entire article about skimming foam from jam, including some helpful pictures and advice from a master food preserver.
You can even put the skimmed foam to good use. Tasting Table recommends turning it into fruit leather or dehydrated into candy-like shards to add to the top of ice cream. You can also try mixing it into a cream cheese, replacing the jammy syrup with the foam in my strawberry rhubarb cream cheese recipe.
More canning questions
If you're new to canning or don't do it enough to feel like an expert - I'm here to help! Let's go over a few things that can be ambiguous or go wrong.
How to tighten metal bands
It's advised to screw the metal bands on until "finger tight." Well that means something different to everyone and I always found it maddening as a beginner.
Nellie Oehler, a food safety specialist at Oregon State University, has a helpful description. She says, "I like to screw on my rings until I feel resistance and then give it a short extra twist. If you tighten it too tight the lids will buckle as the air escapes from the jar. It is normal to have loose rings after you process and the jars cool. They are called self-sealing which means that the metal expands as it heats to allow the air to come out of the jar and then it sort of tightens when it cools but most are a little loose at the end."
Jars that didn't seal
Sometimes a jar or two won't seal. There can be any number of reasons:
- The rim was dirty so the lid couldn't form a vacuum
- The jar rim has a tiny chip in the glass
- There wasn't enough head space
- The metal bands were screwed on too tight
If the jar didn't seal, you can do two things with your strawberry rhubarb jam. You can put it in the fridge and use it right away or you can reprocess it. If you plan to reprocess it, you need to do so within 24 hours and use a new lid. Repeat the process, including boiling it for the entire processing time.
The University of Minnesota has more information on dealing with jars that didn't seal and the possible causes.
Jar sizes
Jams are most often made in half-pint jars. These hold 1 cup of jam (8 ounces). I often make them in cute, little 4-oz jars for gift giving or to pull out for a cheese & charcuterie board.
You can also use pint jars, according to the National Center for Home Food Preservation, but that's a lot of jam!
More recipes & resources
If you're looking for other strawberry rhubarb jam recipes, these might interest you:
- Strawberry rhubarb jam that uses apples instead of pectin - By Nourish + Nestle
- Strawberry rhubarb jam for the freezer (no canning) - by The Busy Baker
- Strawberry rhubarb jam with pectin by Food in Jars
- A jam with more strawberries than rhubarb - by Barnardin
- Strawberry rhubarb jelly from National Center for Home Food Preservation
See what else is in season at the same time as strawberries & rhubarb.
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