Wash and drain the currants. Place the currants on their stems in a pot and heat slowly until juice is formed. Let it boil up carefully. Stretch a cloth over a pot and add the berries with the juice. Squeeze the fruit in the cloth. Measure 500 ml of the juice produced. If there is less juice, measure the amount and mix with the same amount of jam sugar plus 10%.
Mix juice and jam sugar and bring to the boil while stirring. As soon as the mixture boils, add citric acid and let it boil for 2 minutes while stirring. Stir from time to time. Remove the pot from the heat and stir in the crème de cassis. Immediately fill jelly into prepared glasses, close them tightly and put them on the lid for about 5 minutes. Turn over again and let cool completely