How to Make Awesome Jam From Fresh Plums

Close-up of two slices of toast spread with homemade plum jam, on a wooden board, next to a bowl of jam and a wooden knife

Toast with butter and fresh plum jam. [Photographs: J. Kenji López-Alt]

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Before this summer, I never really understood the need for jamming. I mean, theoretically I understood it: You have more fruit than you can eat or give away, so, rather than let it go to waste, you find a way to preserve it for future use. But simply knowing those facts is different from being faced with a tree that drops five pounds of fruit per day into my backyard, in the same way that reading about hang gliding is different from being shoved off a cliff strapped to a flap of canvas.

When I lived in the city, I got my fruit from the farmers market or the supermarket in easy-to-manage batches. If I was going to make jam, I had to plan on making jam in advance. This summer I made jam because, aside from letting the fruit rot on the ground, I literally had no other choice.

I gave away as many plums as I possibly could to neighbors. I packed bags of them and brought them on road trips. I ate plums three meals a day. I even fed plums to the dogs (don't worry, not the pits). It wasn't enough. Over the course of the three weeks during which the tree was bearing ripe fruit, I picked over 80 pounds of plums. That's a lot of plums.

As you can imagine, I got quite a bit of practice at making jam. This is a summary of what I learned, along with some step-by-step instructions on how to make it yourself using your own plums (or plums from the farmers market or supermarket).

Close-up of a hand holding a whole fresh plum, next to plum slices

The Keys to Great Plum Jam

Here's the most important stuff I learned after making many batches of jam.

  • Start with super-ripe plums. The riper the better. I mean it. It's better to have plums that are on the verge of decaying than to have plums that are too firm. If you get your plums from your own tree, the best plums are the ones that hang like water balloons and fall off at the merest touch, or, better yet, the ones that have fallen to the ground already, if you can get to them before birds or bugs do. At the farmers market, see if your farmer has crates of overripe fruit under the tables or left over at the end of the day. You can usually get a discount on it.
  • Macerate overnight. Some recipes have you combine plums and sugar directly in the pot and start cooking right away. Eventually the plums break down and you can make jam—but the process is much easier if you macerate the plums the day before and let them rest in the fridge overnight, so that the sugar can draw out flavorful juices and dissolve. Your finished jam will cook faster and thus have a fresher, less-cooked flavor.
  • Keep the sugar level low. I use about a pound and a half of sugar per four pounds of plum flesh. For jams, this is pretty low on the sugar spectrum, but add much more and the jam gets cloying. (You'll need more sugar if your plums are anything less than perfectly ripe, but why would they be?) Because sugar contributes to proper jam texture, you need to add a secondary gelling agent that works even without sugar. I use Pomona's Universal Pectin, which uses calcium to activate gelling, precluding the need for tons of sugar.
  • Skip the lemon juice. Most plum jam recipes I've seen out there call for lemon juice for flavor balance and textural adjustment. But after trying jam with lemon juice and jam without, side by side, in various quantities, I've found that even a small amount distracts from the fresh plum flavor.
  • Use a wide pan to cook. The wider your pan, the more easily water will evaporate, and the more quickly your plum jam will reduce. Quick reduction leads to fresher flavor.
  • Keep it chunky. I cut my plums into quarters and let them break down naturally as they cook. This creates a nice chunky texture with juicy pieces of plum in the final mix. If you like a bit more jamminess to your preserves, you can run half of the plums through a food mill (we like the OXO Food Mill).

How to Make Plum Jam From Fresh Plums

Step 1: Pit and Quarter the Plums

A hand holding a whole fresh plum while a knife cuts into the fruit

If you're using a loose-stone variety of plum, you can simply cut them around the equator, twist the halves apart, and discard the pits. But for clingstone varieties, like these elephant heart plums, it's easiest to cut the pit out with a knife.

I start by slicing down one side of the plum parallel to the natural seam in the fruit, a little bit off center. This matches the orientation of the pit, so it maximizes the amount of fruit you can get off in one stroke.

Close-up of cutting wedges of plum off of the whole fruit, while a hand holds the fruit in place

Once you've taken off both sides, you can then trim around the pit with the tip of your knife to remove any excess material.

A hand holding a plum pit with some fruit surrounding it, with sliced fruit on a wooden board nearby

You should end up with a pit with just a bit of flesh stuck to it. (Feel free to suck on those pits to get at that flesh—it's tasty!)

Sliced plum fruit on a wooden board next to a chef's knife, with a large metal bowl of whole plums nearby

Five pounds of plums should leave you with about four pounds of plum flesh when you're done trimming. And keep those skins on, because much of a plum's aroma lies in those skins!

Step 2: Macerate

Two hands lifting a pile of sliced plums in a metal bowl to toss them with sugar

Transfer the plums and any juices from the cutting board into a large bowl (the largest you've got, most likely), and add a pound and a half of granulated sugar and one tablespoon of pectin for every four pounds of fruit. Toss the plums, cover with plastic wrap, and refrigerate overnight until they've released their juices.

Close-up of a large spoon lifting a spoonful of macerated sliced plums from a large bowl

The next day, things should look nice and soupy.

Step 3: Freeze Spoons

Three spoons placed on a rack in the freezer, with various plastic containers and freezer bags nearby

Put a few metal spoons in the freezer before you start cooking. These will help you determine when your jam is ready down the line.

Step 4: Start Cooking

Because you've already extracted so much liquid, the plums will break down very quickly when you start to heat them on the stovetop. The key to great flavor is to use a really wide-mouthed pan.

I used either my wide Dutch oven or my sauté pan, depending on how big a batch I was cooking.

Add the plum mixture to your pot, and stir in four teaspoons of calcium water. (Look for the instructions on your pectin package for proper dilution rates for calcium water.) Place the pot over medium heat and cook. Make sure to stir frequently as the jam cooks to prevent any scorching on the bottom.

Step 5: Mill the Plums

A food mill placed over a metal bowl, with drippings from milled plums visible underneath and drops of plum juice on the outside, next to another bowl of macerated sliced plums

As soon as the plums have broken down slightly, they should be tender enough to mill. Running them through a food mill will break them down to give you a smoother texture in the finished jam.

A hand using a flexible spatula to scrape milled plums from a metal bowl back into a pot on the stove

I mill about half of my plums, then scrape them back into the pot.

Step 6: Keep Cooking and Skim

Close-up of a large spoon resting at the top of a pot of cooked plums, with a layer of foam on the top

Keep cooking the plums—you want to cook them down enough that they reduce by about one-quarter.

As they cook, a layer of foamy scum will appear on the surface. Skim it off if you want your jam to stay nice and glossy. A small amount of butter added to the pot will also help reduce foaming.

Step 7: Test for Doneness

As the jam starts to get thick and glossy (this should take 15 to 30 minutes or so), it's time to check for doneness. Place a small amount on one of your frozen spoons and return it to the freezer.

A wooden scraper spoon dripping liquid from cooked plums into a frozen metal spoon

Let it rest for five minutes, then check on the jam. It should be firm, but not rubbery, and should just cling to the spoon if you tip it.

At this stage, you're pretty much done. You can chill your jam, store it in the fridge, and eat it within a few weeks, or you can process it in jars to store at room temperature for several months.

Step 8: Clean and Fill Your Jars

A hand lifting a glass canning jar out of a sink full of water holding many glass jars, metal lids, and metal rings

To start jarring, wash and sterilize all of your jars in hot soapy water, then rinse them out thoroughly. You want them to be quite hot when you're jarring to prevent thermal shock from adding the hot jam mixture to them.

Filling a jar with hot homemade plum jam by squeezing it from a flexible plastic container, with a large pot of jam visible in the background

If you have one of those fancy jamming funnels, go ahead and use it, but I find that a plastic deli container is the best device for scooping food from one location to another with minimal dripping.

Wiping the rim of a glass jar full of plum jam, using a paper towel

Wipe off the rims of the jars once they're filled.

A hand holding a jar of plum jam wrapped in a towel, while the other hand screws on a metal canning lid and ring

Cover the jars and screw on the lids until they're snug but not overly tight. Screwing a Mason jar lid too tight will actually create a weaker seal, as it will damage the threads in the lid.

Step 9: Process the Jars

Process the jars in a boiling-water bath according to manufacturer instructions.

Close-up of jars of plum jam, topped with metal lids but no rings

Take the plums out of the bath and let them cool at room temperature. Do not try to rush cooling by placing them in the fridge or under running water (unless you like jam and broken glass everywhere, that is).

If a proper seal has formed, the buttons on the tops of the lids should depress as they cool—and they'll make a really satisfying ping as they depress.

A fingertip pressing on the center of the metal lid on a sealed jar of plum jam

Once the buttons have depressed, unscrew the lid rings so that you can clean around the lids with a damp cloth one more time. If you have a good seal, there should be no risk of those lids popping off.

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Finally, screw the rings back on, let the jars cool naturally, and remove the lid rings once again for storage. Storing with the rings off ensures that you're aware if one of your jars loses its seal.

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.

Two slices of toasted bread spread with butter and plum jam, on a wooden board, next to a wooden spreading knife

Now I just need to find someone who'll take 12 quarts of fresh plum jam off my hands!