On medium heat, heat the milk to 185°F, stirring frequently. Use a candy or meat thermometer to be accurate.
Remove the milk from the heat and cool to 115°F.
Stir in 1/4 cup of yogurt from a previous batch. You may use plain, good quality store bought yogurt if this is your first batch.
Pour yogurt into individual jars, if desired, and keep warm for 6–8 hours, or until set. 110°F–115°F is ideal. (See post for ideas on how to keep warm without using a yogurt maker).