Use plain yogurt with live active cultures
Heat milk to about 180°F to 200°F
Cool the milk to about 110°F to 115°F
Stir in 2 to 3 tablespoons of yogurt per quart of milk
Mix gently until fully combined
Pour the mixture into a clean container
Cover the container
Keep it warm at about 110°F to 115°F for 4 to 12 hours
Check for thickness and tanginess
Refrigerate the yogurt for several hours
Save a few tablespoons of the finished yogurt for the next batch