Pick or buy three pounds of ripe blackberries on a hot August afternoon. Add sugar, add lemon, cook, jar, invert. This is the one you make in your grandmother's kitchen, the one that ends up in your pantry every year for the rest of your life.
Method is the traditional French inversion / self-pasteurization. Full mechanics are on the Jamming 101 hub.
Ingredients
- 1.5 kg (about 3⅓ lb) wild or cultivated blackberries, ripe, weighed after rinsing and draining
- 1.2 kg (about 2⅔ lb) granulated white sugar
- Juice of 1 lemon (approximately 30 ml)
That's the whole recipe. No pectin, no butter, no spice. Wild blackberries carry plenty of natural pectin and acid; you don't need to add either.
Equipment
- One Le Parfait jam jar set (the 8-jar 324ml set covers this batch with one to spare). Shop here.
- A wide, heavy-bottomed pot, 5+ quart capacity.
- Long-handled wooden spoon.
- Sugar/candy thermometer.
- Wide-mouth funnel and ladle.
- A fine-mesh sieve (only if you want a seedless jam; see Step 4a).
- Clean cotton kitchen towels.
- A chilled plate for the gel test.
Method
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Rinse and inspect the fruit.
Tip the blackberries into a colander, give them a quick rinse under cool water, and pick out any leaves, stems, or unripe (red) berries that snuck in. Drain well. Wild berries are dustier than supermarket ones; don't skip the rinse.
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Warm the jars.
Run the jars and lids through a hot dishwasher cycle, or rinse with kettle-boiled water. Leave them warm until you need them.
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Combine and start the cook.
Tip the drained blackberries into your pot. Add the sugar and the lemon juice. Stir gently to coat. Set over medium-high heat. The berries will start to release juice in about 5 minutes; once they do, raise the heat to high and bring to a rolling boil.
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Cook to a set.
Boil hard, stirring frequently. Skim the dark purple foam as it rises. After about 15 minutes, the jam will start to thicken noticeably. Run the cold plate test at 20 minutes: a teaspoon on the chilled plate, wait 30 seconds, push with a fingertip. If it wrinkles and holds shape, you're done. If it runs, give it another 3 minutes and re-test.
You're aiming for 220°F / 104°C on the thermometer. Wild blackberries can take 5 to 10 minutes longer than cultivated ones because they hold more water; don't pull the pot off the heat early just because the time-on-clock matches the strawberry recipe.
The cold-plate gel test -
(Optional) Strain for seedless.
If you want a seedless jam, after the gel test, pass half the cooked jam through a fine-mesh sieve set over a clean bowl, pressing the solids with the back of a wooden spoon. Stir the strained portion back into the pot with the seedy portion to keep some texture. (Going fully seedless is fine too; you'll lose about 25% of the volume to the sieve.)
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Fill the jars hot.
Funnel and ladle. Fill to within ¼ inch of the rim. Wipe the rim. Seat the twist lid and tighten to hand tight.
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Invert.
Upside-down onto a clean towel, at least one minute, five to ten preferred.
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Flip and cool.
Right the jars and leave undisturbed for 6+ hours. Listen for the lid pop.
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Check, date, store.
Press the center of each lid. Sealed lids are concave and firm. Date and label. Cool dark cupboard, 12 months sealed. Refrigerate after opening.
Recipe Notes
On wild vs. cultivated. Wild blackberries are smaller, seedier, more acidic, and more flavorful. Cultivated supermarket blackberries (often the Marion or Triple Crown varieties) work in this recipe but the result is slightly milder. If you can get to a bramble in August, that's the move. If not, farmers' market blackberries are the next best option.
On seediness. A jam with seeds throughout has a more rustic, traditional texture. A fully seedless jam is closer to a jelly. Most French households make it seedy. Half-and-half (Step 4a) is a nice compromise.
On timing. Blackberry season runs late July through early September in most of the US, with peak ripeness in mid-August. Buy or pick when the berries are deep matte black, not glossy; matte means fully ripe.
On variations. Add a vanilla bean (Step 3) for blackberry-vanilla, a teaspoon of star anise (Step 3) for blackberry-anise, or 30ml of red wine (replace some of the lemon juice volume) for an adult-tasting blackberry-cassis-style preserve.
Frequently Asked Questions
- Do I need to add pectin?
- No. Wild blackberries are unusually high in natural pectin, particularly slightly underripe ones. The sugar-and-acid-and-heat triangle does the gelling work without any commercial pectin.
- Can I use frozen blackberries?
- Yes. Thaw fully in a colander over a bowl, then add the released juice back to the pot. The jam will set slightly softer than a fresh-fruit version; cook 3 to 5 minutes longer to compensate.
- My jam is too tart. Can I add sugar mid-cook?
- Yes, in small amounts. Stir in an additional 100g (about ½ cup) and bring back to a rolling boil for 2 minutes. Re-test the gel. Wild blackberries vary in acidity, so this is a normal adjustment.
- Why are there small white spots in my finished jam?
- Almost always sugar crystallization, which means the sugar wasn't fully dissolved before the boil started, or the jam was cooked past 222°F / 106°C. Cosmetic only; jam is still good. Next batch, stir gently over low heat until the sugar fully dissolves before raising to a boil.
- Can I scale this recipe down?
- Yes, easily. Halve everything and use the 4-jar set. The cook time will be about 5 minutes shorter. Don't try to scale below ½ batch; the pot-to-fruit ratio gets awkward and the cook becomes harder to control.