Working with MILK in Cold Processed Soap

Every soapers know to work with milk in soap means to be very careful with the temperature. When making soap with high sugar liquid such as milk and honey, the temperature needs to be kept low at all time to prevent scorching the milk or burning the honey (there are other methods when working with honey, we'll share to you soon).

Working with Milk in Cold Processed Soap
Cold Processed Soap made with Fresh Goat's Milk

When lye (NaOH, we’re talking bar soap here) is added to water, the exothermic reaction causes temperature to rise tremendously, likewise when adding lye to milk. The process has to be done slowly and carefully. Many soapers shared their methods and tips and each of them has their own saying as to the BEST METHOD when working with milk in soap.

Before we look at the best ways to work with milk in cold processed soap, let’s look at the soapmaking process briefly:-

Cold Process Soap Making
Add lye to water > Add the lye water into oils > Mix well and blend to “trace” > Mold > Gel Phase/ Or Prevent Gel > Unmold and Cut > Allow to Cure for 4-6 weeks to ensure full saponification

Now, let’s look at the methods shared and tested by MoodTree when using milk in cold process soap:-

Milk as Water Substitute – Frozen Milk Method
Use milk to substitute the whole water called for in the recipe. Freeze the milk into ice cubes (completely frozen, not just slushy). Add lye to the frozen milk slowly. By that I mean about 1 tablespoon of lye at a time, stir until the lye is completely dissolved before adding the second tablespoon. The milk may turn slightly yellowish (which is totally acceptable) or sometimes thicken up due to the lye starting to react with the fats in the milk (work quicker!). If there is undissolved lye at the bottom, make sure the undissolved lye is filtered out before adding to the oils. Undissolved lye will cause lye pockets (lye beads in the soap) making the soap unusable.

If everything goes right, the soap should appear creamy colour with a light tan if it is not gelled (you can pop into the fridge or freezer to prevent gel phase). If the soap is allowed to gel, it will turn a dark tan.

If the milk turned brown when lye is added (probably too much at a time), it is obviously burnt. It will still make good soap but you’ll get a brown soap and probably get white specks inside the soap (caused by overheated then crystallized sugar). This may also happen if the soap went through gel phase. Temperature rise during gel phase and the soap batter will be very hot.

Coffee and Milk Soap full of white specks - find out why here

Half Water, Half Milk – Milk in Oil
Lye is added to half the water called for in the recipe. The other half of the water substituted with milk, is added to the oil mixture. When the lye solution cool down to room temperature, add them into the oil mixture, SLOWLY. I tried this method and noticed that the temperature will rise once the lye solution is added to the oil mixture so add lye solution SLOWLY into the oil mixture while hand-stirring continuously to ensure they are well mixed. Then continue with the soap making process (stick-blend to trace, pour into mold).

Half Water, Half Milk – Frozen Milk & Frozen Water
Half water and half milk are frozen into ice cubes. Add lye to the frozen water and milk, SLOWLY. Again, I mean about 1 tablespoon at a time and stir until the lye is completely dissolved before adding the next tablespoon of lye. There may still be sediments in the lye solution, just filter them out before adding to the oil mixture.

Half Water, Half Milk – Add Lye Water to Frozen Milk – MOODTREE’s Choice
Prepare lye solution beforehand i.e. add lye to half water called for in the recipe. Keep the lye solution covered and chilled. A thin layer will form on top of the lye solution if left exposed to air; if that happens, stir it. Add the chilled lye solution to frozen milk cubes slowly and keep stirring until well mixed. Then stir them into the oils and continue with the soap making process (stick-blend to trace, pour into mold).

Powdered Milk method – No Brainer
If you’ve made milk from milk powder before, you will know that it dissolves easier in hot water so the heat does not bother the milk. Prepare the milk with distilled water and let cool to room temperature then add lye and stir until lye is dissolved. Again, cool to room temperature then stir into the oil mixture. Continue with the soap making process (stick-blend to trace, pour into mold).

Milk powder can also be added to the half water half milk method by add the milk powder to the half water – kind of make up to full milk instead of half milk.

We tried all the above methods except milk powder method as we used only fresh milk. And I almost forget to mention about ice bath. In order to keep the temperature of the soap batter low, it is recommended to submerge the mixing bowl in ice bath throughout the process before molding (i.e. starting from the very first step where lye is added to water/ milk).

We don't use ice bath, instead using cool pack (ice bag). Sometimes we skip this totally since we're usually doing Lye Water to Frozen Milk method; just have to be extra patient while waiting for the lye water to cool to room temperature; and add the lye water to oil mixture a bit at a time while keep on hand-stirring.

Have you worked with milk in cold processed soap before?

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