How do you make goat milk soap: replacing water with milk
Work out the recipe as if you were using water, then use the same weight of goat milk in place of some or all of that water. The lye amount stays the same; only the liquid changes. Because lye heats liquids a lot and milk scorches, makers freeze the milk and add the lye slowly.
What changes and what doesn't
- The lye doesn't change. It depends on the oils, the superfat and the purity, not on the liquid.
- The total liquid doesn't change. Milk takes the place of water gram for gram.
- The milk's own fat, sugar and solids aren't counted. Soap Ledger, like most calculators, treats a liquid that replaces water as if it were all water, and says so next to the line. Goat milk is mostly water, but not entirely.
Worked example
1000 g of oils (Olive oil 50%, Coconut oil 25%, Shea butter 20%, Castor oil 5%), 5% superfat, 100% NaOH, 33% lye concentration:
| Liquid | NaOH | Goat milk | Water | Total liquid |
|---|---|---|---|---|
| All water | 138.5 g | 0.0 g | 281.3 g | 281.3 g |
| Half milk | 138.5 g | 140.6 g | 140.6 g | 281.3 g |
| All milk | 138.5 g | 281.3 g | 0.0 g | 281.3 g |
The free calculator on this site works out the total liquid; weigh that amount as milk, or split it between milk and water. In the Soap Ledger app you can add goat milk as its own line that counts toward the recipe's liquid.
Keeping the milk from scorching
When lye dissolves it heats the liquid, and Soap Queen notes milk can reach about 200 °F and scorch. Their method: freeze the milk in cubes, add the lye a little at a time while stirring, optionally set the container in an ice bath, and check that every flake has dissolved before you go on (Soap Queen (Bramble Berry): Creamy goat milk soap). Cold liquid dissolves lye more slowly, so take your time.
Milk sugars can make the soap overheat in the mold, so the same recipe chills the soap after pouring and lets it sit a few days before unmolding (Soap Queen (Bramble Berry): Creamy goat milk soap).
Adding milk another way
Some makers dissolve the lye in a smaller amount of water and add the milk to the oils or at trace instead. If you do, the milk still counts toward the total liquid: take the same weight off the water, and make sure enough water is left to dissolve the lye fully.
Lye safety. Verify every weight before you make this, and follow lye safety. Not a safety or compliance certification. Eye protection, gloves and covered skin; ventilation and a clear, uninterrupted workspace.
Try it in the lye calculator. Work out the lye and total liquid, then weigh that liquid as milk.
Sources
Written for Soap Ledger in our own words. Numbers in the examples are calculated by Soap Ledger's engine when the page is built. Last updated .