The day before, rinse a measuring cup and the glasses of the yoghurt maker with boiling water. Heat the milk in a pot to 42°C. Take the pot off the stove. Stir the ferment carefully into the milk. Pour the milk mixture into the glasses using the measuring cup.
Close with the lids.
Let the glasses mature for 6-8 hours in the yoghurt maker. Do not move the yoghurt maker during this time, as the bacteria will be disturbed and the yoghurt will not become so firm.
The next day, take the glasses out of the yoghurt maker and let them ripen in the refrigerator for another 10-12 hours.