Put the currants with their stems in a large saucepan, mash them with a pounder, add 1 liter of water, bring to the boil and simmer over a medium heat for 10 minutes.
Stretch a juice cloth between 4 chair legs. Pour in the fruit and collect the liquid. Stir sugar into the juice, bring to the boil again. Skim and stir with the preserving aid. Fill into boiled bottles while hot and close tightly. Store in a dark and cool place.