How to make blueberry jam

Two problems, one fix

Pectin needs an acidic environment to gel, and blueberries have very little acid. They also have only moderate pectin, mostly in the skins.

Separately, the flavour of a blueberry is gentle and slightly one-dimensional, and concentrating it with sugar makes that worse rather than better. A blueberry jam without acid tastes like sweetened purple.

Lemon juice — generously, the juice of two lemons per kilo of fruit — addresses the set and the flavour at the same time. Some cooks add the zest as well, which is worth doing.

The method

A short cook, so the fruit does not go to purée. FoodHQ does not publish keeping times, jar-processing schedules or the acidity figures that decide whether a sealed preserve is safe on a shelf. In the UK the Food Standards Agency is the authority — follow its guidance on sterilising, sealing and storing.

1. Weigh the blueberries. Set aside a third of them to add later if you want whole fruit in the jam.
2. Put two thirds in a preserving pan with a splash of water and the juice and zest of two lemons per kilo.
3. Simmer for five minutes, crushing the fruit against the pan side so the skins burst and release their pectin.
4. Put two plates in the freezer. Add sugar — equal weight, or jam sugar if you want certainty — and stir over a low heat until dissolved.
5. Bring to a rolling boil, then add the reserved whole berries.
6. Boil for five to eight minutes and test on a cold plate.
7. Stand for ten minutes before potting so the whole berries do not all float.

Variations

• Blueberry and lemon, using zest as well as juice, which is the default and the best.
• Blueberry and lime, sharper still.
• Blueberry and bay, with a leaf simmered in and removed. Unexpected and very good.
• Blueberry and thyme, in the same spirit.
• Blueberry and cinnamon or cardamom, for a warmer, more autumnal preserve.
• With a proportion of blackcurrant or redcurrant, which supplies pectin and acid and deepens the flavour.
• Frozen blueberries work perfectly and go straight into the pan.

What to expect

Set

Softer than a currant jam even with lemon. Jam sugar gives a firmer result if you want one.

Colour

Deep purple. The skins carry the colour and it deepens with cooking.

Wild bilberries

Much more intense and more acidic. A far better jam, if you can pick enough.

Sugar

Equal weight is standard. Less gives a fresher preserve that will not keep as long.

Lemon quantity

Two lemons per kilo. This is more than most recipes suggest and it is the right amount.

Common questions