Why It Works
- The right ratio of plums to sugar gives you bright plum flavor without overwhelming sweetness.
- Keeping half of the plums in large pieces produces a jam with nice chunks.
- Macerating the plums a day in advance means less cooking time on the stovetop, which leads to better flavor.
A bright, not-too-sweet jam made from fresh summer plums.
Disclaimer: Because I don't use lemon juice in my recipe, there's a chance that if your plums are particularly low-acid, they may not be 100% safe to store at room temperature. If you are the type to err on the side of safety, I recommend storing the jam in the fridge and consuming it within a couple of months, or adding one and a half ounces of lemon juice to the mixture as it reduces.
- 4 pounds (1.8kg) pitted black or elephant heart plums, unpeeled, cut into quarters
- 1 1/2 pounds (675g) granulated sugar
- 1 tablespoon Pomona's Universal Pectin (optional; see note)
- 4 teaspoons (20ml) calcium water (see Pomona's pectin package for instructions)
- 1 teaspoon (5g) unsalted butter
Combine plums, sugar, and pectin (if using) in a large bowl and toss. Cover and refrigerate for at least 8 and up to 24 hours.
Place a few metal spoons in the freezer. Transfer plum mixture to a large, wide pot and stir in calcium water. Cook over medium heat, stirring occasionally to prevent scorching. Simmer until plums are mostly softened, about 15 minutes. For a smoother jam, place a food mill over a bowl and ladle a few cups of the mixture into it. Mill the mixture into the bowl. Repeat until roughly half the plums have been milled, then stir the milled plums back into the pot.
Continue to cook until mixture starts to foam. Scrape off and discard foam using a metal spoon. Stir in butter. Continue to cook, stirring occasionally to prevent scorching, until foaming has subsided, about 15 minutes longer. Continue to cook, stirring more frequently, until jam is glossy, about 10 minutes longer.
To test for doneness, spoon a small amount of jam onto one of the frozen spoons and return to freezer for 5 minutes. Remove from freezer and check consistency. The jam is ready when it's spreadable, but not runny. Cook until this texture has been reached.
Transfer jam into washed and rinsed Mason jars. Seal jars and process according to manufacturer instructions. Store or serve.
Use Pomona's Universal Pectin if you want a stronger-setting jam. It's preferable to standard pectin in this case, as it works well even with relatively low-sugar jams, like this one.