Can I use milk in soap?
Short answer
Yes. Milk makes a very mild, creamy bar, but its sugars and proteins scorch easily, so it must be kept cold and soaped without gel.
Explanation
The book's method: freeze the milk in ice-cube trays first. Make the lye solution with chilled water only and let it cool to about room temperature. Add the frozen milk to the cooled lye and stir until melted, keeping it ideally below 30 °C. Combine with oils at 25–28 °C, blend in very short bursts to a light trace, pour into individual molds, don't insulate, and freeze for 3–5 hours or overnight. Cure 8–10 weeks.
If milk soap turns orange-brown and smells burnt, the milk scorched or the soap gelled.
What to do
- Keep everything cold, from milk and lye to oils and molds.
- Over-blending creates heat; use short bursts.
Source: The Big Book of Homemade Soap — Goat Milk & Honey Soap: The No-Gel, Low-Temperature Technique