Pick the red currants, you can leave the stems. Put the berries in a big pot and leave at least ¼ of the pot empty so it won´t boil over.
Pour water in the pot so that the berries are covered. You can also preheat the water in a teakettle to make the process faster.
Add the sweetener, use erythritol for a sugarfree version. Also honey or regular sugar works well.
Boil the mix for around 5-10 minutes so that the berries become soft.
Taste the juice and add more sweetener if you want to.
Let the mix cool. After a couple of hours it is ready to put in bottles, but you can let it rest through the night also, just cover with something so no flies get in it.
Strain the juice with a strainer to a bowl. Press the berries so you get all juice out.
Pour the ready juice into freezer bottles using the funnel as help. A soup scoop is good for this job. You can also use glass bottles if you store the juice in fridge.