Select, wash and drain the currants and blackberries. Juice the berries with a berry press (yields approx. 0.75 l). Do not throw away the skins and seeds (it is best to save them for liqueur).
Mix jam sugar, berry juice and 100 ml black currant liqueur. Bring to the boil and simmer while stirring for about 5 minutes. Immediately pour into hot rinsed twist-off glasses. Close tightly and place on the lid for about 5 minutes.
Turn the glasses back over. Let them cool down.