Making Milk Soaps
As discussed earlier, you can replace part or all of the water in a recipe with milk to make an extra-rich soap. You can use cow's milk, half-and-half, goat's milk, or buttermilk. Once you've mastered making soap with milk, you can try any kind of milk you can find!
Of all the ways there are to make milk soap, the most effective one requires working with frozen milk. If you add lye to room temperature milk, it will curdle and turn brown, becoming a hideous, stinky mess. You also need to work with oils that are as cool as they can be without resolidifying.
Some soapmakers prefer to add powdered milk partway through the process. If you decide to do that, make sure the powder is well-incorporated. You want to observe the heat restrictions as outlined below in the recipes. Low temperatures are key to successful milk soap.