How to Make Cold Process Soap

As the long-term effects of antibacterial soaps become more widely known, people are turning to more natural alternatives. This movement has resurrected the art of soap making. If you are new to making soap you are in for a real treat! It can seem like a daunting undertaking at first but it is such a rewarding process.

No farmer’s market would be complete without the beautiful array of homemade soaps. It is wonderful to support these local vendors but if the price-tag is out of reach for you, don’t despair. You can still ditch the antibacterial soaps by making your own homemade cold process soap!

Cold Process Soap vs. Hot Process Soap

The method you choose is a matter of personal preference. This post is to teach you about cold process soap but you can take the same recipe and use the hot process method instead.

Both of these methods begin in the same way. You make a lye/water solution and mix it with the oils to begin saponification. To make a cold process soap you would incorporate any additives and pour it into the mold as soon as it reached trace (more about trace later).

For hot process soap you would let the soap batter “cook” in a slow cooker on the lowest heat to accelerate and complete saponification. Then you would stir in your additives and mold it.

Cold process soap takes 4-6 weeks to completely saponify and be ready to use. In theory, hot process is ready to use immediately. However, it is wise to let it sit a week or so to harden a bit. This will make it last considerably longer.

I have made soap both ways and I like each method for different reasons. Cold process soap is easier to pour into the molds so if you are trying to use a mold with a design or pattern I would recommend cold process.

How Is Soap Made?

Soap is a chemical reaction that occurs as a result of mixing an animal or vegetable fat with a base (sodium hydroxide). This chemical reaction is called saponification.

Merriam-Webster defines saponification as “the hydrolysis of a fat by an alkali with the formation of a soap and glycerol.” OK, so what does that mean?

Each fat has a unique combination of triglycerides. Triglycerides are compounds made up of a single molecule of glycerol and 3 fatty acids. Each combination requires a different amount of alkali to complete the saponification process. The alkali in soap-making is sodium hydroxide, also called lye.

The lye is mixed with water to create a basic solution. This solution is then mixed into your fats. As they are combined and begin to react, the glycerol molecule is separated from the fatty acids. The fatty acids then react with the hydroxide ions in the lye solution. This is saponification.

Worried About Lye?

As I covered in-depth in this post, it isn’t truly possible to make soap without lye in some part of the process. Lye is the necessary agent for saponification and any true soap, even one you buy, is made with it. You can purchase a pre-made soap base but it is much less budget friendly.

Cold Process Soap Instructions

1. Prepare your mold. Wood molds will need to be lined with freezer paper or wax paper. Silicone molds are ready to use as is. You can also use any box if you line it with freezer paper, wax paper, or a thick garbage bag.
2. Put on your protective gear, place the glass jar on the scale and tare your scale. Pour distilled water into the jar until it reads 12.54 oz. Set aside.
3. Put the second jar on the scale and tare the scale. Carefully pour lye into the jar until your scale reads 5.09 oz.
4. In a well-ventilated area or outside, slowly pour the lye into the water. Stir the mixture until the lye is dissolved. It will become quite hot so be careful if you need to move it. Let this mixture sit and cool to between 100-120 degrees.
5. While the lye is cooling, measure all other ingredients EXCEPT the essential oils and warm them together in your pot or slow-cooker. Once they are melted, remove the oils from the heat and let cool to between 100-120 degrees. I use the infrared thermometer about every 5-10 minutes to test the temperature. This works really well but a candy thermometer placed in each container also works. If one is cooling faster than the other you can put your oils back on the heat source or the lye/water mixture in a warm water bath to slow the cooling process a bit. Ideally, you want the lye/water and the oils to both be between 100-120 degrees and within 10 degrees of each other.
6. When the temps match, slowly pour the lye/water into the oils. BEFORE you turn your stick blender on, make sure the blade is completely under the mixture or you will splash it everywhere. Use the stick blender to bring the batter to a light trace. It should be slightly thick and resemble cake batter.
7. Now would be the time to add essential oils, but it is completely optional.
8. Blend essential oils in by pulsing the immersion blender a few times. This should bring the mixture to a medium trace. You can tell when you have reached a medium trace by lifting your blender up out of the mixture (in the OFF position) and observing how the drips behave. They should leave a trail or “trace” on the surface. If you don’t use essential oils, just pulse your blender a few more times to bring it to medium trace.
9. Pour the soap batter into your prepared mold. Use the spatula to get it all out. Remember that the soap is not fully “cooked” yet at this point and could still irritate your skin so you should still be wearing your gear.
10. Put the mold somewhere it can sit for 24 hours.
11. Place an upside down cardboard box over the soap and cover with a towel. If your house is warm the towel may not be necessary.
12. Let sit for 24 hours. You can now remove your soap and cut it. This recipe in the silicone loaf mold makes about 12 bars weighing approximately 4.5 oz each, but you can cut them whatever size you like.
13. Stand bars up in a dry area with an inch or so of space in between to allow for air circulation and let them sit for 4-6 weeks. This will allow the soap to complete the saponification process. The soap will also lose some of its water during this time making the bar harder. The harder the bar, the longer it will last.
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