diy yogurt recipe You heat a gallon of milk to 120 degrees and add a cup of yogurt with live cultures (after your first batch just save some yogurt from the previous batch). Stir well and pour the milk mixture into mason jars and put on the lid. Then, place the jars in the oven with the light on for 12-24 hours. The light is the perfect amount of heat to culture the yogurt. Then, let it chill in the fridge and it’s ready.