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.
Before my first summer spent in a house with a backyard, I never really understood the need for jamming. I mean, I understood it theoretically: 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).
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.
- For refrigerator jam, skip the lemon juice. Since plums vary in acidity, most plum jam recipes call for lemon juice to ensure safety (as well as for flavor balance). 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. So, if you do not plan to can your plum jam for long-term storage, I recommend skipping the lemon.
- 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, Step by Step
Step 1: Pit and Quarter the Plums
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.
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.
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!)
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
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.
The next day, things should look nice and soupy.
Step 3: Freeze Spoons
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
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.
I mill about half of my plums, then scrape them back into the pot.
Step 6: Keep Cooking and Skim
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.
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
To start canning, wash all of your jars in hot soapy water, rinse them out thoroughly, and place them on a round rack in a deep stockpot. Fill the pot (and jars) with water to cover and bring to a boil. This will sterilize the jars and get them piping hot. You want the jars to be hot when you're filling them to prevent thermal shock, as well as to ensure the jam gets heated thoroughly during processing.
If you have a canning funnel, 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.
Wipe off the rims of the jars once they're filled.
Cover the jars and screw on the lids until they're snug but not overly tight. Screwing the ring of a canning jar too tightly will actually create a weaker seal: A tight ring keeps hot air inside the jars from escaping while processing, resulting in a weaker vacuum when they cool.
Step 9: Process the Jars
Process the jars in a boiling-water bath for 10 minutes.
Carefully take the jars 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.
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.
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.
Now I just need to find someone who'll take 12 quarts of fresh plum jam off my hands!
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 notes)
4 teaspoons (20ml) calcium water (optional; see Pomona's pectin package for instructions)
2 1/2 ounces bottled lemon juice (5 tablespoons; 75 ml; see notes)
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. Thoroughly wash 6 pint-sized canning jars and their lids. If you plan to process the jam for shelf-stable storage, prepare a water bath and sterilize the jars as described in our canning guide. 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 and bottled lemon juice (see notes). 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 prepared canning jars and wipe any jam from the rims. To store in refrigerator, simply place lids on jars, screw on rings, and let cool completely at room temperature before refrigerating. To process jam for shelf-stable storage, bring water bath to a rolling boil. Place lids on jars and screw on rings until they are snug but not overly tight. Carefully lower jars into the boiling water bath and process for 10 minutes. Remove jars and let cool completely at room temperature. Unprocessed jam can be refrigerated for a couple of months; Processed jam can be stored in a cool, dark place for up to 1 year.
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.
If you do not plan on processing this jam for shelf-stable storage, omit the lemon juice for the best flavor.
|Nutrition Facts (per serving)|
|Amount per serving|
|% Daily Value*|
|Total Fat 0g||0%|
|Saturated Fat 0g||0%|
|Total Carbohydrate 9g||3%|
|Dietary Fiber 0g||1%|
|Total Sugars 9g|
|Vitamin C 2mg||9%|
|*The % Daily Value (DV) tells you how much a nutrient in a food serving contributes to a daily diet. 2,000 calories a day is used for general nutrition advice.|