Heat the milk over medium heat, stirring often, until it reaches 180°F.

Remove the pot from the heat. For thicker yogurt, hold the milk around 180°F for 5 to 10 minutes, stirring often.

Let the milk cool to 110°F to 115°F.

Place the plain yogurt starter in a clean jar or bowl.

Add a small amount of the warm milk to the starter and stir until smooth.

Pour the starter mixture back into the remaining warm milk and stir gently.

Pour the milk mixture into clean glass jars.

Cover the jars with lids, plastic wrap, or a clean towel.

Place the jars in a warm incubation spot around 105°F to 115°F.

Incubate for 8 to 12 hours for mild yogurt, or 12 to 24 hours for tangier yogurt.

Once set, move the yogurt to the refrigerator.

Chill for at least 4 hours before serving.

For Greek-style yogurt, strain the chilled yogurt through cheesecloth or a fine mesh strainer until thick.