Add charcoal to milk in a large saucepan over medium-high heat; cook until it reaches 180 degrees, stirring occasionally to prevent scorching, once at temperature shut down and let cool to 115 degrees. Whisk together 1 cup milk and the yogurt. Stir into remaining milk. Let stand undisturbed in a warm place until yogurt has the consistency of custard, usually around 6 hours. Whisk and transfer into desired containers. Refrigerate and let set. Usually around 1 hour. If you desire a thinker yogurt you can place in cheese cloth over night. Serve with favourite granola and berries.