Wash and remove the stems from red currants, stone the sour cherries, carefully clean the raspberries, put everything in a large saucepan, mix with Gelfix and sugar, possibly chop the fruit with a hand blender.
Bring to the boil while stirring, simmer for at least 3 minutes, skimming if necessary.
Pour the jam into scrupulously clean, hot-rinsed screw-top jars and close tightly while still hot.