Blueberry Jam
A glossy, deep-purple small-batch jam made from just blueberries, sugar, lemon, and a pinch of salt — no boxed pectin required. Blueberry skins carry plenty of natural pectin, so a brisk boil with fresh lemon juice takes the fruit from soupy to spoon-coating in about 20 minutes. The result is spreadable but not stiff, bright with lemon, and tastes intensely of ripe berries rather than plain sugar.
Combine 600 g (4 cups) blueberries with 300 g (1 1/2 cups) sugar, 2 tablespoons lemon juice, and a pinch of salt in a wide, heavy pan; mash about half the berries, let them sit 10 minutes to draw out juice, then boil hard, stirring often, for 15–20 minutes until the jam reaches 104°C (220°F) or a dollop wrinkles on a freezer-chilled plate. Ladle into clean jars, cool, and refrigerate — it thickens noticeably as it chills, and no added pectin is needed.
- Use a wide, heavy-bottomed pan: more surface area means faster evaporation, a quicker set, and fresher berry flavor.
- Trust the frozen-plate test over the clock — if a chilled spoonful wrinkles when you nudge it, the jam is done.
- Pull it at 104°C (220°F) even if it looks loose; hot jam is always runny and firms dramatically as it cools.
Equipment
- Wide, heavy-bottomed 4-quart (4 L) saucepan or Dutch oven
- Potato masher
- Heatproof spatula or wooden spoon
- Small plate, chilled in the freezer (for the set test)
- Ladle
- Two clean 8-ounce (240 ml) glass jars with lids
- Instant-read thermometer (optional)
食材
Jam
- 600 g fresh blueberries, or frozen — no need to thaw
- 300 g granulated sugar
- 30 ml fresh lemon juice, from about 1 large lemon
- 2 g finely grated lemon zest, optional, for a brighter jam
- 1 g fine sea salt
步驟
- 步驟01
Put a small plate in the freezer for the set test later. Rinse the blueberries, drain well, and pick out any stems or shriveled berries. Zest and juice the lemon.
- 步驟02
In a wide, heavy-bottomed pan, combine the blueberries, sugar, lemon juice, zest (if using), and salt. Crush about half the berries with a potato masher, leaving the rest whole for texture. Let stand 10 minutes, stirring once or twice, until the sugar is wet and the berries are juicy.
- 步驟03
Set the pan over medium-high heat and stir until the sugar fully dissolves. Bring the mixture to a full rolling boil — one that doesn't calm down when you stir.
- 步驟04
Keep the jam at a brisk boil, stirring often and scraping the bottom so nothing scorches. Skim off any pale foam that collects at the edges. After 15–20 minutes the bubbles will turn small and glossy, the jam will coat the spatula, and a thermometer should read 104°C (220°F).
- 步驟05
Pull the pan off the heat. Spoon a little jam onto the frozen plate and return it to the freezer for 1–2 minutes. Push the blob with a fingertip: if the surface wrinkles and it moves slowly, it's set. If it runs like syrup, boil 3 minutes more and retest.
- 步驟06
Let the jam sit off the heat for 5 minutes so the fruit distributes evenly instead of floating, then give it a stir and ladle it into clean jars, leaving about 1 cm (1/2 inch) of headspace.
- 步驟07
Cool the jars to room temperature, then seal and refrigerate. The jam finishes setting as it chills — give it a few hours (or overnight) before judging the final texture.
Make ahead
This jam is a natural make-ahead: the flavor rounds out and the set firms after 24 hours in the fridge. For pantry storage, ladle the hot jam into hot sterilized jars with 6 mm (1/4 inch) headspace and process in a boiling water bath for 10 minutes; sealed jars keep up to a year in a cool, dark cupboard.
Storage
Refrigerate in clean, tightly sealed jars for up to 3 weeks. For longer keeping, freeze for up to 6 months — leave 1 cm (1/2 inch) of headspace so the glass doesn't crack — and thaw overnight in the refrigerator. Always use a clean spoon to keep the jar fresh.
Variations
Maple Blueberry (refined-sugar-free)
Swap the granulated sugar for 240 ml (3/4 cup) pure maple syrup. Because syrup adds liquid, expect 5–8 extra minutes of boiling and a softer, spoonable set. Store in the fridge and use within 2 weeks.
Lemon-Vanilla
Use the full teaspoon of lemon zest and stir in the seeds of 1/2 vanilla bean (or 1 teaspoon vanilla extract) right after the jam comes off the heat. The vanilla softens the berries' tartness and makes the jam taste almost pie-like.
Warm-Spiced
Drop a cinnamon stick and a small pinch of ground cardamom into the pot for the boil, then fish out the stick before jarring. Excellent on toast in cooler months and alongside soft cheeses.
Serve with
Nutrition per serving
Nutrition values are estimates based on the metric measurements. Adjust as needed.
常見問題
Do I need pectin for this blueberry jam recipe?
No. This blueberry jam recipe relies on the natural pectin concentrated in blueberry skins, plus fresh lemon juice for acidity. A hard boil to 104°C (220°F) evaporates enough water for the natural pectin to gel, so the jam sets on its own — boxed pectin would only make it stiffer and require more sugar.
Can I use frozen blueberries?
Yes, and you don't need to thaw them first. Add them straight to the pan with the sugar; they'll release juice as they warm. Expect the total boil to run about 5 minutes longer since frozen berries carry a little extra moisture.
Why is my jam runny, and can I fix it?
Usually it just wasn't boiled long enough, or it was judged while still hot — jam thickens a lot as it cools, and even more after 24 hours in the fridge. If it's still loose the next day, scrape it back into the pan, boil hard for 3–5 minutes, and redo the frozen-plate test. Worst case, you have an excellent blueberry syrup for pancakes.
Can I reduce the sugar?
You can drop to about 200 g (1 cup) for a refrigerator jam, but expect a softer set, a slightly less glossy finish, and a shorter fridge life of around 2 weeks. Don't go much lower than that — sugar is doing real work here for both texture and preservation.
Is this jam safe for water-bath canning?
Yes, as long as you keep the full 2 tablespoons of lemon juice, which keeps the acidity in safe range. Ladle the hot jam into hot sterilized jars with 6 mm (1/4 inch) of headspace, wipe the rims, and process in a boiling water bath for 10 minutes, adjusting for altitude.
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