Ingredients:

  • 4 lbs fresh blackberries
  • 4 cups granulated white sugar
  • 2 tbsp fresh lemon juice

Instructions:

  1. Rinse blackberries thoroughly and pat dry.
  2. Place berries in a wide-bottomed heavy pot and use a potato masher to crush them roughly, releasing the juices.
  3. Optional: For seedless jam, press the crushed berries through a fine-mesh sieve into the pot, discarding the seeds.
  4. Stir in the granulated sugar and lemon juice over medium heat.
  5. Bring the mixture to a rolling boil, stirring constantly to ensure the sugar dissolves completely and doesn't stick to the bottom.
  6. Maintain a steady boil, skimming any foam that rises to the surface with a spoon.
  7. Insert a digital candy thermometer into the jam (without touching the bottom) and continue boiling until the mixture reaches 220°F (104°C).
  8. Perform the plate test by placing a small spoonful of jam on a frozen plate for 30 seconds; if it wrinkles when pushed with a finger, it has reached the setting point.
  9. Carefully ladle the hot jam into sterilized jars, leaving 1/4 inch of headspace.
  10. Wipe the rims clean, apply lids, and tighten. Process in a boiling water bath for 10 minutes for shelf storage, or allow to cool for refrigerator storage.