Blackberry jam is the classic use for a hedgerow glut, and it needs nothing more than fruit, sugar and a little lemon. There is no need for added pectin: the lemon juice helps it set, and a proper boil does the rest. If you have picked more blackberries than you can eat, this is where to start.
What You'll Need
- 1kg blackberries, picked over and rinsed
- 800g granulated sugar
- Juice of 1 lemon (about 3 tablespoons)
Method
- Prepare. Put a saucer in the freezer for testing the set, and wash your jars and lids and warm them in a low oven to sterilise.
- Soften the fruit. Put the blackberries and lemon juice in a large, heavy-based pan and cook gently for about 10 minutes, crushing lightly, until the fruit is soft and juicy.
- Add the sugar. Add the sugar and stir over a low heat until every crystal has dissolved.
- Boil to setting point. Bring to a rolling boil and cook hard for 10 to 15 minutes until the jam reaches 105C, or wrinkles when a spoonful is pushed on the chilled saucer.
- Pot and seal. Skim off any scum, leave the jam to settle for 10 minutes, then ladle into warm sterilised jars and seal at once.
Getting a good set
Blackberries are only moderately high in pectin, which is why the lemon juice matters. Slightly under-ripe berries carry more pectin than very ripe ones, so a few red ones in the pan will not hurt. If the jam has not set after the first boil, return it to the heat for a few more minutes and test again. It is the same method I use in my loganberry jam and blackcurrant jam recipes.
Using your blackberries
If you would like a smooth, seedless preserve instead, try my bramble jelly, or bake a blackberry and apple crumble. For where to pick, see my blackberry foraging guide.
Troubleshooting
Runny jam. It probably needs a little more boiling. Return it to the heat for a few minutes and test again on a chilled saucer.
Too stiff. If you boiled it too long, loosen it by stirring in a splash of hot water while it is still warm.
Too many seeds? Blackberry pips are noticeable in jam. For a smoother result, press half the cooked fruit through a sieve before adding the sugar, or make bramble jelly instead.
Storing your jam
Sealed in sterilised jars, the jam keeps for around a year in a cool, dark cupboard. Once opened, keep it in the fridge and use it within a few weeks. Using less sugar gives a fresher taste but a shorter shelf life, so store lower-sugar batches in the fridge.
Frequently Asked Questions
Do I need pectin to make blackberry jam?
No. Lemon juice and a proper boil are enough to get a set with blackberries.
How do I know when blackberry jam is set?
It should reach 105C, or wrinkle when a spoonful is pushed on a chilled saucer.
Can I use frozen blackberries?
Yes. Add them straight to the pan without thawing.
