Heat one liter of milk to 82°C / 180°F or bring to a boil. Let it cool down to 42-44°C / 108-112°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 4 to 5 hours or until the yogurt has reached the desired firmness.
Refrigerate for about 8 hours to stop the incubation process.