Heat the Milk: Pour the milk into your kettle and heat over medium heat until it reaches 180°F. Stir occasionally to prevent scorching.
Cool the Milk: Remove the kettle from the heat and allow the milk to cool to 130°F. To speed up this process, you can place the pot in a sink partially filled with cold water, stirring the milk gently to help it cool evenly.
Prepare the Gelatin: While the milk is cooling, soak the gelatin in the cold water for about 5 minutes or until softened. This will allow the gelatin to bloom, which helps it dissolve smoothly into the warm milk.
Combine Ingredients: Once the milk reaches 130°F, stir in the sugar or stevia (if using). Then, add the bloomed gelatin and stir thoroughly, breaking up any clumps. Make sure the gelatin is fully dissolved.
Add the Culture: Sprinkle the freeze-dried culture evenly over the surface of the milk or add the plain yogurt. Let it sit for about 5 minutes. (This allows freeze-dried cultures to rehydrate.)
Incubate the Yogurt: Pour the yogurt mixture into your glass jars or other storage containers, leaving about 2 inches of headspace. Place the containers in your oven with the oven light on. This is the easiest way for me to provide a gentle, consistent temperature for incubation. Let the yogurt sit overnight or for 8-10 hours. For a thicker yogurt, incubate longer. If your oven light doesn't provide enough warmth (around 100-110°F), you can also incubate the yogurt in a warm place, such as on a heating pad or in a cooler with hot water about ¾ the way up the mason jars.
Chill and Enjoy: In the morning, transfer the yogurt containers to the refrigerator and chill for at least 4 hours to allow the yogurt to thicken further and develop its full flavor.