Step 1

Place milk in a large, heavy saucepan over medium heat. Heat, stirring often, until a thermometer inserted into the milk reads 180 degrees F (82 degrees C). Turn off heat and let milk cool, stirring often, to 115 degrees F (46 degrees C).

Step 2

Pour about 1 cup of warm milk from the saucepan into a bowl and whisk in yogurt. Pour this mixture back into the saucepan and stir to combine. Ladle the liquid yogurt into clean glass jars and cover loosely with lids.

Step 3

Place the jars in a warm spot in your kitchen, wrapped in a towel if your kitchen is breezy. Let incubate until yogurt thickens, 12 to 24 hours.

Step 4

Move the jars to a refrigerator to cool.