Blackberry Strawberry Jam

blackberry strawberry jam recipe

One way to keep experiments safe in the fridge

I’ve been thinking about wild blackberry jam. There’s nothing at all wrong with a basic approach: combining blackberries with sugar and lemon juice and cooking the mixture until it sets. You don’t need to add pectin, you can keep the volume of sugar relatively low,  and you’ll get a fine result. (You can find some examples of this simple process in other posts on this blog: Blackberry Chambord Jam, Boysenberry Jam, and Tayberry Jam.) But blackberries have been bugging me, anyway.

They’re one of my favorite fruits, a summertime sine qua non. That means I want to love the jam as much as I love the blackberries themselves — but I don’t, quite. When I imagine wild blackberry jam, I want it to be luscious and soft, even though it still has some seeds. (I usually remove about half of them.) But the reality is usually a jam that’s a lot firmer and much more dry than my dream jam should be.

One way to change the texture of the jam would be to significantly increase the amount of sugar in the recipe, but I tried that and really couldn’t stand it. I decided to find out whether strawberries would work to smooth and plump up the texture, and I do like how it turned out. This jam is mostly blackberry, and it tastes that way, but the strawberries work a little bit of magic in the jar, enriching the flavor and easing the gritty tendencies of those wild California fruits.

Join me in the experiment, if it appeals to you . . .

blackberry strawberry jam recipe

Green light!

Blackberry Strawberry Jam

3 pounds wild blackberries
1 pound strawberries
2.5 pounds sugar
4 tablespoons lemon juice

1. Sterilize your jars and put 5 teaspoons on a plate in the freezer, to test your jam for doneness later.

2. Carefully pick over the blackberries, removing any stray thorns or brambly bits. Rinse them only if necessary — that is, only if they’ve been sprayed or subject to vehicle exhaust. (Better to pick them in an unmolested spot far from the road.)

3. Rinse, hull, and roughly chop the strawberries (unless they are small to begin with, in which case you can leave them whole)

4. Combine the berries, sugar, and lemon juice in a large glass or ceramic bowl, cover tightly, and let rest in the refrigerator for up to 24 hours. (By allowing the fruit to macerate in this way, you’re creating a flavorful, pectin-rich juice while at the same time allowing the sugar to initiate the preserving process. It’s much better than letting those berries sit on their own in the fridge.)

5. When you’re ready to make the jam, transfer the contents of the bowl to your jam pan. Heat the mixture on medium, stirring frequently until the sugar is fully dissolved. Then turn up the heat and bring the mixture to a boil, stirring as needed to prevent sticking or burning. (If it really wants to stick, turn down the heat a bit.) Use a shallow, stainless-steel spoon to skim the stiff foam off the top of the mixture as it cooks. In my 11-quart copper jam pan, the total cooking time is about 25 minutes. Watch the mixture and test it when it starts to thicken up, the foam settles down, and the bubbles become small and shiny.

To test your jam for doneness: Remove the pan from the heat. Use one of your frozen spoons to scoop up a little bit of jam — not a whole spoonful. Return the spoon to the freezer and wait 3 minutes. Retrieve the spoon and hold it vertically. If the mixture just fails to run and is thick and gloppy when you push it with your finger, it’s done. If the jam isn’t ready, cook it a few minutes more.

6. When the jam is done, bring it back to the point where it just begins to boil and immediately remove it from the heat. Extract some of the seeds from the jam by quickly pressing 3-4 cups of the very hot mixture through a stainless steel sieve. I use the back of my wooden cooking spoon to work the jam through the sieve, holding it directly over the pot. (This entire step is optional; you can make fully seeded jam if you prefer. If you do remove some seeds, consider this: Instead of discarding them, you can toss those jammy leftovers into a quart jar with a few cups of vodka and an extra handful of sugar. Shake the jar once or twice a day and, ten days later — you’ll have blackberry strawberry liqueur.)

7. Ladle or pour the jam into sterilized jars, leaving 1/4-inch head space. Wipe the jar rims clean and secure the lids. Process 10 minutes in a hot-water bath canner.

Yields about 6 half pints.

blackberry strawberry jam recipe

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12 comments to Blackberry Strawberry Jam

  • This sounds so good. I am going to Seattle at the end of the month and I hope I’ve timed my trip in the middle of blackberry season up there so I can make some jam (and a pie!).

    • Shae

      Thanks, Yossy! Our blackberries are coming in kind of late here, so maybe you’ll get blackberries up there, too. I have heard that where California wild blackberries tend to be drier (and therefore seedier), Washington’s are often plump but perhaps a tad on the watery side. And Oregon is supposed to be the sweet spot. So you’ll have to let us know what you think of Washington wild blackberries! My suspicion is that they’re all good. :-)

  • Cheryl

    Sounds yummy!

    Total novice question – why do I always hear about copper pans for cooking down jams? Is there something special about copper or will any wide, shallow pan work?

  • Earlier this year the wild blackberries on our property were loaded with blossoms and, later, little green berries. Then the temperatures started rising and the rain stopped falling, and the only blackberries I got were the first few to ripen that went straight into my mouth. I wasn’t willing to pay the prices being asked around here so maybe next year . . .

  • Diana

    Thanks and Great timing! I’m planning on going blackberry picking this weekend. But since the strawberries are long gone around these parts, maybe I’ll supplement with some tart apples a la the Ball Natural Jam. I tried it with blueberries earlier this summer and it was fantastic!

  • Wondering how to convert pounds of berries to cups? I have no way to weigh them (LOL)

    • Shae

      Hi Jolene: I’d say about 3 1/2 cups of blackberries to a pound, and about 4 cups of strawberries to a pound. A kitchen scale is a handy thing to have!

  • Jess

    This looks super yummy! last year we picked 30+lbs from our yard and i couldnt find enough recipes to do stuff with, i am excited to try this! If I cut the sugar down would it do anything to the consistency and preserving process?

    • Shae

      Hi Jess: Sorry I was away and unable to respond to your comment until now. You may already have experimented with this, but my answer is yes, if you cut the sugar down it will change the consistency of the jam and also the cooking time. I tested many versions and amounts before deciding that this was the best texture and right level of sweetness for me. You may find you prefer different proportions.

  • My honey and I have been making Blackberry jam for the last month. We live in Northern Calif. where we have wild berries everywhere. When they are over here in the valley, we ride up 20 minutes to the mountains and pick there. We bought a food mill for the removal of the seeds and it works perfect..