Wash and chop the strawberries. Peel the grapefruit (I took pink). Ideally, very generously straight away so that the white skin is also removed. For 400 g you need about 3 medium-sized ones. Also cut into small pieces.
Mix the strawberries, grapefruit, Gelfix and sugar in a large saucepan and let the juice steep for about 30 minutes.
Bring to the boil over medium heat and bring to the boil for four minutes. If you like, you can go through with the hand blender, I left it a little bit more chunky.