Instructions

1. 1

   Sort through the blueberries, picking out any leaves, stalks and soft or unripe berries.

2. 2

   Wash the berries thoroughly in plenty of cold water and drain them well. Berries from the woods grow close to the ground and therefore need washing particularly carefully.

3. 3

   Crush about a third of the berries with a fork or a potato masher so that they release their juice and the jam sets well later.

4. 4

   Squeeze the lemon. Slit the vanilla pod lengthways and scrape out the seeds with the back of the knife.

5. 5

   Mix the blueberries, lemon juice, vanilla seeds and the preserving sugar 2:1 in a tall pan and leave them covered in a cool place until the sugar has dissolved.

6. 6

   Sterilise four screw-top jars of 250 ml each and their matching lids in a large pan of vigorously boiling water, then lift them out with tongs and leave them to drain on a clean cloth. Only sterile jars will keep the jam for a long time.

7. 7

   Bring the mixture to the boil while stirring, then let it boil hard over full heat, stirring constantly and skimming off the foam. This activates the preserving sugar and makes sure the berries are properly cooked through.

8. 8

   For the set test, put a blob on a cold plate; if it firms up after a minute the jam is ready. If it stays runny, boil it for another minute and repeat the test.

9. 9

   Fill the boiling hot jam straight away into the prepared jars to about 1 cm below the rim, wipe the rims with a clean cloth and screw the lids on tightly at once.

10. 10

    The jars do not need to be turned upside down; simply leave them standing and let them cool completely. As they cool, the lids pull inwards audibly.