plums for making plum jam“splat”

Every night, for the past week, we’ve been awakened by the sound of fat, juicy plums plummeting from the trees in our backyard to the ground. We pick them as fast as we can, but some are simply out of reach, and others just sneak up on us, ripening suddenly and then hurling themselves out of the tree.

We somehow managed to pick about six pounds of plums before I decided that something must be done.

So, as I did last year, I decided to make plum jam.

A few things have changed, though, since I last made jam. First of all, I moved. Last year’s plums were harvested in the heart of the Mission: small yellow plums that were subtle and pleasantly sweet-tart. We managed to spin those into many jars of jam and chutney before we moved.

Secondly, I realized that over the past year I’ve learned a bit about pectin. The jam we made last year, while delicious, was a bit thin and watery. I wasn’t about to make that mistake again. Pectin causes jams and jellies to gel, and some fruits have more and some have less. Apples, it turns out, have a lot of pectin. So when you are trying to make jam with fruits that are low in pectin, like berries or plums, it’s a good idea to use an apple, peel and all (trust me, you will never know it’s even in the jam). Also, you need the right balance of pectin, acid, and sugar with the fruit to make it all balance and gel correctly.

Anyway, here in our new house we have not only one, or two, but four different plum trees. Lucky for the trees that I love plum jam too, since they’ve been somewhat neglected over the years (we unfortunately moved just after the plum harvest last year and missed the whole thing). And lucky for me that my husband is tall and can reach all those rogue plums, even though we still wake up every morning to a smattering of plums.

Plumalicious Jam

plum jam

Makes: 13 half-pint jars

About 12 cups (about 6 lbs) pitted and roughly chopped plums
1 or 2 green apples
Juice of 1 lemon or lime
2 lbs granulated sugar
2 small plates in the freezer

1. Cut up all the plums and put them into a heavy, 5-quart stockpot.

put plums in 5-quart stockpot

2. Grate the apple, skin and all (but not the core), on a box shredder-grater. Add the apples, lemon or lime juice, and sugar to the plums.

grate the apple on a box shredder-grater

3. Stir the plum mixture thoroughly, place over medium-high heat, and bring to a boil.

plum jam cooking

4. Lower the heat to medium and let boil, skimming the foam occasionally and smashing the fruit as it cooks. Boil for about 20 minutes.

plum jam cooking

5. When the jam starts to look thickened, start testing it by spooning a small amount onto one of the chilled plates. This will chill it quickly and let you see how thick it is. Keep testing it until the jam is thick enough, but don’t cook it longer than about 30-35 minutes. If it’s not thick enough for your liking, next time add an extra apple. Don’t worry, the jam will still be great.

6. Once the jam has thickened, get your clean jars set up. You can re-use the glass jars, but you should get new lids and rings each time. If you have a canning funnel, it makes your life a lot easier for filling jars.

plum jam jars

7. Fill each jar to about 1/2 inch from the top, leaving a little breathing room. Screw on the lid, but not too tight.

plum jam in jar

8. Turn the jars over at once so they stand upside down on their lids and let them cool to room temperature. This should seal the lids. If the lids are sealed, the top will be indented. You can store the jam in a cool dark place for up to a year. If not, store in the refrigerator and use within about 1 month.

plum jam jars turned over

Plumalicious Summer Plum Jam 10 July,2008Kim Laidlaw

  • I know jams can be made without processing for short-keeping, despite what the government says, but I’m faintly alarmed to see you propose the upside-down method for sealing — that’s been a no-no for a while.

    it’s better to use very very very hot jars and work fast. or, you know, process the jars in a boiling-water bath. inverting is a pretty good way to get leaks.

    Regardless, I would definitely not advise keeping unprocessed preserves any longer than a month or two.

  • Love the grating idea! Thanks so much for writing about making jam. So easy, actually, and very much a part of celebrating the seasons.

    If you’d like, mixing in just a few plums that are still green will provide enough pectin for setting. Or generally use plums that aren’t all the way ripe, which helps balance the sweetness of the sugar, too.

    I’ve been putting up jam for about 20 years and long ago stopped processing in water bath and yes, keep the jars on my shelf for much longer than USDA would officially allow. (But then, I cook and eat my meat far below what they recommend, too.) Have never had any trouble.

    Inverting is an old short-cut for hot-processing, though I don’t use it because I think it’s important to keep jam off the lid and think the potential for air cavities at the bottom of the jar is much higher with this method. Along with Anita’s reminder to work with hot jars, I’d say that if you’re boiling your fruit to the right temperature, it’s a very low number of jars that won’t give off that satisfying, air-tight “pop.”

    And the one or two that don’t, well, those are the first you eat. Anyway, most folks who receive a jar of your homemade jam are more than happy to open it right away for a taste and then keep it in the fridge.

  • kim laidlaw

    I actually learned that technique from a well-respected chef. I use spotlessly clean jars and very hot jam, and only save the jars that “pop” in my pantry (all others are stored in the fridge and eaten first). They all sealed (unlike when I’ve processed them and about half seal). And Thy is right, I give em all away and they are typically eaten within a month anyway. But certainly, if you are concerned you should definitely follow the USDA official method of sterilizing and processing jars. In fact, in my previous jam post from last summer (which I’ve linked to in this post) you will find links to some good websites which walk you through that process.


Kim Laidlaw

Kim Laidlaw is a cookbook author, editor, food writer, producer, project manager, and baker who has been in the kitchen covered in flour since she was big enough to stir the biscuit dough. She has over 16 years of experience in book and online publishing, and a lifetime of experience in the kitchen.

Her first cookbook, Home Baked Comfort, was published in 2011; her second cookbook, Baby & Toddler On the Go, was published in April 2013; and her third cookbook, Williams-Sonoma Dessert of the Day, was published in October 2013.

She was the first blogger on KQED’s Bay Area Bites blog, which launched in 2005, and previously worked as a professional baker at La Farine French Bakery in Oakland, CA. She lives in Petaluma with her husband and their child, whom she cooks for everyday. Find out more at

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