Cold Process Soap Using the Heat Transfer Method

The Heat Transfer Method for making Cold Process soap uses the heat from the Sodium Hydroxide (lye) when mixed with water to melt hard oils and butters.

This can save time in the soap making process, but is considered a more advanced process of soap making.

Step 1: Mix the Lye With the Water.

**Before attempting this process, please make sure you are very well versed on lye safety. Read all safety information on the container, in the material safety data paperwork from the manufacturer and follow all safety guidelines.**

Instead of melting the hard oils (palm oil and coconut oil) and butters (cocoa butter, shea butter, avocado butter, mango butter, etc...) using a microwave, a hot plate or the stove, you can use the heat generated when the lye is mixed with the water. The temperatures when the lye is mixed with water can reach around 200 degrees Fahrenheit (around 93 degrees Celsius).

I combine the hard oils and butters in one container and the liquid oils with any additives that will be used in another container.

Step 2: Introduce the Lye to the Hard Oils

Mix the lye water in the container with the hard oils and butters and mix with a lye safe utensil (I use a silicone spatula).

The process can take about 10 minutes for the hard oils and butters to completely melt and it will lower the temperature of the mix in the process. Then add the liquid oils and the temperature will lower further.

Combine using a hand blender (also called an immersion blender). A whisk can be used, but it will take much longer to reach emulsion (when the lye and the oils and butters have combined).

Step 3: Working With Colors and Fragrance

You can remove some of the liquid oils ahead of time to mix with micas, pigments and/or oxides.

The benefit to this is if you have a design or technique in mind for the soap, mixing the soap batter in already mixed colors will keep the soap more fluid.

Depending on the fragrance or essential oils used, you can mix it at the same time the color is mixed in using the emulsion blender or mix separately using a whisk or the silicone spatula.

The type of fragrance or essential oil can determine how quickly the soap batter can thicken. The higher temperature from the Heat Transfer Method can speed things up even further.

Step 4: Pouring the Soap in the Mold

The soap is now ready to pour in the mold. In this instance, I'm using a technique called the In the Pot Swirl.

Most of the soap batter of each color all goes in one bowl which is then poured in the soap mold all at once.

I keep a little of the soap batter aside for applying to the top in order to make a decorative design.

Step 5: Cut the Soap

After 24 to 48 hours, the soap is hard enough to be cut.

Then it will need to cure for anywhere from 4 to 6 weeks. The longer it cures, the harder the soap bar will be and the longer it will last.

One additional benefit is during that curing time, the room smells wonderful.