Stone fruit · Fruit Plum
Plum Jam with Cardamom and a Firm Set
Published 11 Oct 2026 · Reading time 4 min
Why this one works
Plums have plenty of pectin but it hides in the skin, and plum skin is also where the tartness lives. The result is that plum jam made from peeled fruit is both sweet and loose, while the same fruit cooked skin-on sets firmly and tastes of something. Keep the skins, keep the acid, and let cardamom bridge the two.
In the pan
- 1.6 kg plums, a third underripe and hard
- 750 g granulated sugar
- 2 tbsp lemon juice
- 8 green cardamom pods, crushed and tied in muslin
- 1 tsp high-methoxyl pectin, whisked into 1 tbsp of the sugar
The numbers
- Family
- Stone fruit
- Fruit
- Plum
- Pectin source
- Natural — skin and underripe fruit, plus 1 tsp insurance
- Sugar ratio
- 1 kg fruit : 750 g sugar
- Target Brix
- 65 Brix
- pH
- 3.2
- Gel point
- 105 °C
- Sealing
- Boiling water bath
- Shelf life
- 24 months
- Crystal risk
- Low
- Yield
- 5 x 250 ml jars
- Time at the pan
- 30 min
Three stages
Prep — quarter, keep the skin, crack the cardamom
Quarter the plums and cut the stones out, but leave every bit of skin attached. Plum skin carries both the acid and most of the pectin, and it softens completely within 20 minutes of boiling, so there is no texture penalty for keeping it.
Crush the cardamom pods with the flat of a knife until the husks split and the black seeds show, then tie them into muslin. Crushing rather than grinding is deliberate: ground cardamom turns the jam grey-green within a month, whole pods do not.
Cook — 20 minutes with the bag, then to 105 °C
Warm the fruit, lemon juice and cardamom bag together for 20 minutes before the sugar goes in. That wait is what pulls the colour out of the skins: a plum jam that gets its sugar immediately ends up a dull purple, while one cooked first turns a clear deep ruby.
Add the sugar, dissolve it, then boil hard to 104 °C. Sprinkle the pectin blend, hold at 105 °C for 60 seconds, and squeeze the cardamom bag against the pan as you lift it out. Test on the chilled plate; plum sets with a clean, slightly chewy break rather than a soft one, which is normal for this fruit.
Seal — 12 minutes, because the gel is dense
Fill warm 250 ml jars at 90 °C to a 6 mm headspace and process for 12 minutes. Dense, skin-on jams conduct heat more slowly than a berry jam, and the extra two minutes is the cheapest insurance in this book.
Plum jam is at its best between three and eight months: the cardamom has had time to spread through the gel but the fruit has not yet lost its edge. Keep a jar back and open it at Christmas.
Failure diagnosis
Four things go wrong with this preserve more often than anything else. Open the one you are looking at.
Will not set
Almost always peeled fruit. Plum pectin is concentrated within 2 mm of the skin, so peeling takes 70 percent of it out. Add 2 tsp pectin, boil 60 seconds at 105 °C, and keep the skins next time.
Graining and crystals
Low risk with the skins left on. If you do see crystals, they are usually calcium tartrate from the fruit rather than sucrose, and they form in the first month then stop — the jam is still perfectly good.
Mould or spoilage
Whole plum quarters float, and the ones that break the surface are the first to spoil. Fill, wait two minutes, and top up with hot jam so every piece is submerged.
Colour loss
The ruby colour turns to a brownish purple after about 18 months, and unlike most fading this one is not purely cosmetic: the same anthocyanins that provide the colour are part of the tartness, so an old plum jam tastes flatter as well as looks darker.
On the same shelf
Other stone fruit recipes, all already published.
Recipes here are for home preserving and are informational only. Canning safety depends on your altitude, your jars and your thermometer — verify with your local extension service before relying on any single number.