How to make plum jam

Why the stones stay in

Plum stones and the membranes around them carry pectin, and simmering them with the fruit extracts it. Some cooks go further and crack a few stones to add the kernels, which contribute a faint almond note — though apricot and plum kernels are a food-safety matter and the Food Standards Agency is the authority on whether and how they should be used.

Practically, stoning raw plums is slow, messy and unnecessary. Cooked, the flesh separates from the stone completely, and the stones rise to the surface where they can be skimmed off with a slotted spoon.

Keep skimming after you think you have them all. There are always a few more, and it is worth counting them roughly against the number of plums that went in.

The method

Ratios are for set and texture. FoodHQ does not publish keeping times, jar-processing schedules or the acidity figures that decide whether a sealed preserve is safe on a shelf. Those are safety numbers set by a food safety authority rather than by a cookery writer. In the UK the Food Standards Agency is the authority — follow its guidance on sterilising, sealing and storing, and treat this page as the explanation of what is happening in the pan.

1. Wash the plums and pull off any stalks. Do not stone them. Weigh them.
2. Put them in a preserving pan with a small amount of water — a splash for ripe fruit, a little more for firm.
3. Simmer gently until the skins have burst and the flesh has collapsed, twenty minutes or so, crushing them against the pan side.
4. Skim off the stones as they float free. Keep going until no more appear.
5. Put two plates in the freezer. Add sugar — commonly an equal weight to the original fruit — and stir over a low heat until dissolved.
6. Boil hard. Plums usually reach setting point within eight to twelve minutes.
7. Test on a cold plate, skim, stand briefly and pot.

Which plums, and what to expect

Damson

The best. Very high pectin and acid, sets effortlessly, and the deepest flavour. Clingstone, so the skim-the-stones method is essential.

Victoria

Good pectin, moderate acid. The standard British jamming plum and reliably successful.

Very ripe plums

Lower pectin and lower acid. Add a lemon per kilo, or include a proportion of firmer fruit.

Japanese-type plums

Watery and low in pectin. Best combined with something firmer, and they will need lemon.

Skins

They stay visible in the finished jam as dark flecks, which is normal and part of the character.

Variations

• Plum and cinnamon, with a stick simmered in and removed.
• Plum and star anise, which suits darker plums particularly well.
• Plum and ginger, with chopped stem ginger stirred in near the end.
• Spiced plum jam with a bag of cloves, allspice and a strip of orange peel.
• Damson jam, made the same way and needing nothing added.
• Plum and apple, if the plums are very ripe and the set is uncertain.
• Plum butter — sieved and cooked much longer with less sugar, to a thick spreadable paste.

Common questions