1. Sterilize your jars. Place the empty, clean jars on a baking sheet or roasting tin. Carefully place in a hot oven (130°C OR 275°F) for twenty minutes. After twenty minutes, turn the oven off and leave them to cool slightly.
2. Halve and stone the plums before adding to a wide-bottomed saucepan.
3. Add the lemon juice and a splash of water to help start the juices flowing. Bring to the boil gently, stirring frequently. Once it’s boiling, reduce the heat and simmer for 20-30 minutes until the fruit is soft and pulpy.
4. Add the sugar, stirring constantly to make sure it doesn’t ‘catch’ and burn.
5. When the sugar has dissolved boil rapidly, skimming any scum away that forms on the top of the jam.
6. Test after ten minutes by dropping a teaspoonful onto a chilled saucer. Leave for 30 seconds and if it wrinkles when you push it with your finger, it’s ready.
7. If it isn’t quite ready, keep boiling and testing every couple of minutes but err on the aside of caution; it’s better to have it a little bit too soft than too firm. If you have a jam thermometer you are aiming for a temperature of 105°C (220°F).
8. Pour into the still warm jars and put the lid on, tightening firmly. As it cools, the metal lid should pop down; any that don’t should be kept in the fridge and used first as they haven’t sealed properly. The rest of the jars will keep for at least a year in a cool, dark place. Once opened, the jar should be stored in the fridge.
9. The colour of the jam will vary depending on the colour of the plums used. Golden plums will produce a straw-yellow jam, while deep red plums will produce a rich, ruby-coloured jam.
Plums are high in pectin, so you don’t need to add any to the recipe. This means you can use normal white or golden granulated sugar instead of jam sugar, which has pectin added to it to help set fruits that are naturally low in pectin.
You can also make it with less sugar if you prefer a slightly sharper, healthier flavour. I’ve made it with 750g of sugar per 1kg of fruit and enjoyed the resulting jam very much, although it all depends, of course, on how sweet the plums are to start with.
For more great recipes for jams, chutneys and relishes see our Jams, Condiments & Sauces recipe collection.