I love milk soaps. My favourite at the moment are butter soaps, but I have an affection for sheep’s milk and buttermilk soaps as well. Nothing beats a milk soap for mildness, and the dense, creamy lather they produce is lovely on the skin.
Milk soaps can be tricky to make, even for an experienced soap maker. Caustic soda can do odd things to dairy products like cause them to curdle, separate, and give off a smell that isn’t unlike the monkey cage at the zoo. While the heavy ammonia scent does fade, curdling and separation are problems that usually result in a failed batch of soap.
To get around these issues, I like to make milk soaps using the hot process method, and I only use powdered milks. I have found there is no appreciable difference between fresh or powdered in the finished soaps, and for my purposes, powdered works much better. The secret is in the slurry.
To make a slurry, I use a couple of tablespoons of oil, either reserved from my batch or added as a superfat. This oil is mixed with the milk powder and stirred to a thin paste. Once this paste is completely smooth with no lumps, the slurry is ready. I add the slurry to the soap after it’s been completely cooked and cooled just slightly. It does take a good bit of stirring, but the end result is well worth the effort.
Making milk soaps this way helps avoid most of the major pitfalls. Because the soap is completely saponified, the milk and caustic soda never meet, so the curdling, separating, and horrible smell don’t occur. But this doesn’t mean this method is foolproof. I have burned the milk by adding it while the soap was still too hot, so allowing the soap to cool slightly is imperative.
Slurries aren’t just limited to milk powders. They can be made with honey, oats, herbs, extracts, or anything you don’t want compromised by caustic, raw soap. I have made oat milk slurries with whisky, coconut milk slurries with carrot, and buttermilk slurries with heather honey. And each time, the soap turned out beautifully. When it comes to hot process soap, slurries are the way forward.