Canning Plum Jam (A Pretty Recipe for a Late Summer Day)

Every summer, I find myself coming back to this recipe. It’s simple enough to do in an afternoon, but the result feels like something special: deep purple jars lined up on the counter, little pops of the lids sealing as they cool. If you’ve got ripe plums, this is one of the easiest ways to turn them into something you’ll use and love.

Ingredients and Tools You’ll Need

My very favorite plums for this are Santa Rosa, which will give you a beautiful color and a little tartness. But any black plum from the grocery store or farmer’s market will work just fine.

• 6 cups crushed plums (about 3 pounds, pits removed; measure after crushing)
• 1 package powdered pectin (do not substitute liquid pectin without adjusting the method)
• 8 cups granulated sugar

How to Make Plum Jam

Prep Your Equipment First

Before you touch the fruit, get your jars, lids, and tools ready. Wash the jars in hot, soapy water, then transfer them to your water bath canner and fill it with water to cover the jars by at least an inch. Set it over medium heat and let it come to a simmer while you prep everything else.

The jars don’t need to be sterilized, but they do need to be clean and hot. Heating them in the canner is convenient but running through the dishwasher or putting them in a 200 degree oven works too.

Wash the lids and rings and set them aside on a clean towel. No need to heat them—modern lids don’t require it.

Prep the Plums

Wash the plums well, remove the pits, and roughly chop them. You don’t need to peel them.

Place them in a large pot and start mashing with a potato masher. Don’t stress about perfectly smooth fruit, you just want to break them up enough so they cook down evenly.

You’ll need 6 cups of crushed fruit. It’s best to measure this after mashing, not before.

Add the Pectin and Bring to a Boil

Once the fruit is crushed, stir in one full package of powdered pectin and set the pot over medium-high heat. Stir frequently to prevent sticking.

Bring the mixture to a full rolling boil—the kind of boil that doesn’t stop when you stir. This is important, because you want the pectin to fully activate before the sugar goes in.

Be patient here. If it looks like it’s boiling but calms down when stirred, keep going. You want that aggressive, bubbling boil.

Add the Sugar and Boil Again

Once you’ve reached a full boil, pour in all 8 cups of sugar at once and stir to dissolve. Bring the mixture back to a rolling boil. It should come back up fairly quickly.

When it reaches a full boil again, set a timer for exactly one minute.

Keep stirring constantly so the bottom doesn’t scorch. The jam will foam up a bit and that’s normal.

Skim Foam and (Optional) Blend

After that one-minute boil, remove the pot from the heat. Skim off any foam from the surface with a spoon. This is optional and is just to make the finished product look clean and clear.

Fill the Jars

Using a canning funnel, ladle the hot jam into your hot jars. Leave ¼ inch of headspace at the top.

Debubble each jar by sliding a chopstick or debubbler tool around the inside edge. Add a little more jam if needed to bring it back up to the correct headspace.

Wipe the rims with a clean, damp cloth. Place the lids on and screw the rings on until they’re fingertip tight.

Process in a Water Bath

Place the jars back into your canner, making sure they are fully submerged with at least 1 inch of water over the tops. Bring the water to a full boil.

Once boiling, set a timer and process for 10 minutes (adjust if you’re at a higher elevation).

Don’t start the timer until the water is really boiling again after adding the jars.

Let Jars Sit and Cool

When the time is up, turn off the heat and remove the lid from the canner. Let the jars sit in the hot water for 5 minutes—this helps prevent siphoning (when jam leaks out as the jars cool too quickly).

Then, use a jar lifter to transfer the jars to a towel-lined counter. Don’t touch or move them for 12–24 hours. You should hear the lids pop as they seal!

Check Seals and Store

After 12–24 hours, check the seals by pressing the center of each lid. It should be firm and slightly concave, with no movement.

Remove the rings, wipe down the jars if needed, and label them with the date. Store in a cool, dark place for up to 18 months.

If a jar didn’t seal, just refrigerate and use it within 2 weeks.

More Ways to Preserve Late Summer

• If you have pears, you’ll love classic pear preserves.
• If you have extra plums, my plum cobbler is a popular and delicious choice.

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