Heat one liter of milk to 82°C / 180°F or bring to a boil. Let it cool down to 23-25°C / 73-77°F.
Dissolve one sachet in a small amount of the cooled milk in a cup. Pour back into the liter of milk and mix well.
Incubate for 9 to 10 hours or until the yogurt has reached the desired firmness.
Refrigerate for about 8 hours to stop the incubation process.