Wash the currants, drain them well, and strip them off the panicles with a fork.
Wash the sour cherries, drain them well, remove the stones and sort the raspberries.
Mix all fruits (together they should weigh 1500g) and extra preserving sugar in a large saucepan. Let the juice steep for 1 hour.
Bring to the boil, stirring constantly, and let simmer for 3 minutes. Immediately fill the jam to the brim in jars rinsed with hot water and seal. Turn the glasses upside down for 20 minutes.