Goat milk contains vitamins, minerals and fats that make it a nutritious and skin-softening additive to soap and a great choice for people with dry skin or eczema. While milk itself has a neutral pH, the final soap is still, like all true soap, mildly alkaline. It is not only wonderfully mild but is also naturally resistant to bacterial growth and so requires no chemical preservation.
Working with milk can be tricky so I recommend being comfortable with the soap-making process before trying it. To incorporate it into a recipe, replace a portion of the water in the lye solution (typically replacing 50-100% of the water). Keep a close eye on the temperature (you may opt to monitor with a stainless steel baking thermometer or simply monitor it for steaming & discoloration) and mix it slowly. If the lye gets too hot it can make very dark soap or worse-yet, the lye may “volcano.” If it gets too cold the soap can fail to saponify completely, leaving free lye in your soap. Keep the temperature above 90F but below 150F. If you want perfectly white goat’s milk, keep the temperature around 90-100F by adding the sodium hydroxide very slowly. I don’t recommend letting the lye’s temperature drop below this range; I feel that the risk of incomplete saponification is too great, especially for beginners.
Here are a few of my tricks for trouble-free goat milk soap, this process replaces 50% off the water in the lye with milk (the higher the fat, the better and it can be pasteurized or not – the lye will kill bacteria).
- Freeze milk in an ice cube tray (or use fresh, cold milk and chill water too).
- Weigh out ½ of the distilled water for the lye solution, per the recipe.
- Add frozen milk cubes until the total liquid weight is reached.
- Add sodium hydroxide SLOWLY and mix continuously (under a hood or outside). The lye solution may be yellowish – the slower you mix, the less the color will be altered. Once dissolved, keep stirring occasionally until you combine it with the oils.
- Keep the solution between 90F and 150F.
- Proceed with combining the oils and lye.