Equipment
Ingredients
Jam Base
- 1000 g blackberries, fresh or frozen, rinsed and sorted
- 800 g granulated sugar
- 45 ml lemon juice, freshly squeezed
Nutrition (per serving)
Method
Place two or three small plates in the freezer. These will be chilled and used later to test the setting point of the jam.
Wash the glass canning jars and lids in hot, soapy water, then rinse well. Submerge the jars in a large pot of boiling water for 10 minutes to sterilize them, then keep them warm until needed.
In a large heavy-bottomed pot, combine the blackberries, granulated sugar, and fresh lemon juice. Stir gently to coat the berries and let them sit at room temperature for 30 minutes to release their natural juices.
Place the pot over medium-low heat and stir constantly until the sugar has completely dissolved. Ensure no sugar crystals remain on the back of your spoon before allowing the mixture to bubble.
Increase the heat to medium-high and bring the mixture to a rolling boil. Continue to boil rapidly, stirring frequently to prevent sticking, until the temperature reaches 105°C/220°F. Skim off any excess foam that forms on the surface during the boil.
Remove the pot from the heat to perform the wrinkle test. Spoon a small amount of hot jam onto one of the chilled plates. Wait one minute, then gently push the edge of the jam puddle with your finger. If the surface wrinkles and feels gel-like, the setting point is reached. If it remains liquid, return the pot to a boil for another 2 to 3 minutes and test again.
Carefully ladle the hot jam into the warm, sterilized jars, leaving about 1 centimeter of headspace at the top. Wipe the rims of the jars clean with a damp cloth and apply the lids tightly.
Allow the sealed jars to cool completely at room temperature, completely undisturbed, for at least 12 hours. The jam will fully firm up and set as it cools down.
Chef's Notes
- Blackberries are naturally moderate in pectin. Adding a handful of slightly underripe, red blackberries to your mixture will significantly increase the natural pectin content and help achieve a firmer set.
- Lemon juice is absolutely crucial for both flavor balance and structural integrity. The acid reacts with the natural pectin in the fruit to help form a stable gel network.
- For a smoother, less seedy jam, you can briefly mash the cooking berries with a potato masher, or pass half the cooked mixture through a fine sieve before jarring.
- Warming your sugar slightly in a low oven before adding it to the warm berries helps it dissolve much faster, reducing the risk of overcooking the fruit before boiling begins.
Storage
Refrigerator: 1 month — Duration applies to opened jars. Properly sealed, water-bath canned jars can be kept at room temperature for up to 1 year.
Freezer: 6 months — Can be frozen in freezer-safe containers. Leave half an inch of headspace to allow for expansion.
