Sterilise your jars and twist-on lids. Put the raspberries in a large heavy-based pan or preserving pan. Lightly sprinkle in the sugar, a third at a time, gently shaking the pan so the sugar is well distributed. Cover and leave for an hour or so for the juices to draw out.
Lightly stir the mixture with a wooden spoon to break up any clumps of sugar. Place over a medium heat and bring to a steady boil, then boil for 5–6 minutes for a soft set jam, or 7–8 minutes for a firmer set. If you want to be sure, you can test for setting point by using the gel test (see page 15).
Remove from the heat and stir lightly (in one direction only) to remove any foam, adding a drop or two of oil if it doesn’t dispel easily. Tip into a wide-necked jug with a good pouring lip, then fill the warm sterilised jars to the brim. Seal at once.
Invert each jar for a minute or so, to ensure the lid is sterilised, then turn the right way up and leave to cool. Store in a cool, dark, dry place. Best eaten within 9 months. Keep in the fridge once opened and eat within 4–6 weeks.
1kg raspberries
650g jam sugar (i.e. with added pectin)
A drop or two of olive oil (if needed)
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