If you'd like to go beyond the basics of cold process soap making, whip up a batch of liquid soap. It requires a bit more patience to make liquid soap than it does to make bar soap. The major difference between liquid and bar soap is the alkali used to saponify the oils. All soap, whether liquid or hard, starts with a simple chemical reaction between oils and an alkali. With bar soaps, the chemical reaction takes place with sodium hydroxide. With liquid soaps, the chemical reaction takes place with potassium hydroxide, which is a specific type of lye for liquid soap. Liquid soap is usually formulated with extra lye to ensure that the oils are properly saponified, so make certain you don't skip a step in order to neutralize the excess lye.
Equipment / Tools
- Basic tools for mixing the lye
- Large slow cooker
- Measuring cups
- Stick blender
- Potato masher and/or flat whisk
- 16 1/2 ounce sunflower oil
- 7 ounce coconut oil
- 5 1/2 ounce potassium hydroxide KOH
- 16 1/2 ounce distilled water for the lye mixture
- 40 ounce distilled water to dilute the soap paste
- 2 ounce boric acid (or 3 oz. of borax mixed into 10 or 6 oz. of water)
- 3 ounce fragrance or essential oil, as desired
- Soap dye or colorant, if desired
Prepare the Lye-Water Solution
A major difference between making liquid soap and bar soap is that that it is a "hot process" soap. Instead of relying on the heat generated by the saponification process, heat is added using a double boiler, oven, or slow cooker. This recipe can be made in a double boiler or the oven, but a slow cooker is preferred. It keeps everything in one pot and lets it cook evenly without the need to monitor the water in a double boiler. To mix the lye water, take the following steps:
- Measure out your oils and put them in the slow cooker on low. You want this mixture to stay at about 160 degrees Fahrenheit (give or take 10 degrees).
- While the oils are heating up, mix your lye-water, using the standard lye-making procedure. If you've never used potassium hydroxide before, don't be alarmed. It's a bit more volatile in the water than sodium hydroxide and makes an odd boiling/groaning sound as it's dissolving. This is normal.
- When the lye-water is completely mixed and clear, slowly add it into your oils. (You don't need to wait until it is cool.) Don't turn the stick blender on just yet. Just stir the oils and lye together. Then, like in cold process soap-making, start using the stick blender. At first, the mixture will seem like it wants to separate, but keep on blending.
Bring the Soap Paste to Trace
Depending on your mixture of oils, it will take a long time to get to trace, possibly up to 30 minutes. "Trace" for liquid soap looks much like it does during the cold process of soap making. It's somewhat pudding-like, or more like a blend of pudding and applesauce, with the characteristic "traces" or ridges that occur when you dribble the soap back into the pot or stir. You can't over stir the mixture, so make sure you've have a good solid trace before moving to the next step.
Cook the Paste
Once the soap has reached trace, you'll need to give the mixture one more good stir, shake off your stick blender, put the lid on the pot, and wait. Check on the soap in about 15 to 20 minutes. If there's any separation, just stir it and put the lid back on. Keep checking on the soap every 20 to 30 minutes.
In the three to four hours it takes this soap to cook, it will transform and go through several stages. Don't worry if you don't see one of the phases. Sometimes a stage will be brief and you'll miss it. The six stages usually look like the following:
- Thick applesauce
- Cooked custard with small bubbles
- Watery mashed potatoes
- Solid taffy
- Chunky/creamy petroleum jelly
- Translucent petroleum jelly
Keep stirring every 30 minutes or so through each of the stages. It will be difficult to stir through the taffy stage. Do the best you can. The potato masher will help break the taffy up. Just when you think the soap will never finish cooking, it will become creamy and move into the translucent petroleum jelly stage.
Test the Paste
Once you've reached the 3- to 4-hour mark, the soap will have softened and turned translucent. At this point, you'll need to time the soap to see if it's cooked long enough. Take these steps to test:
- Take 2 ounces of boiling water in a separate bowl and add in one ounce of your soap paste.
- Stir the soap, breaking it up and helping it dissolve in the water. Once it's completely dissolved (several minutes) check to see how clear it is.
- If the mixture is lightly cloudy, that is a good sign that the soap is ready. The soap will "settle" after it's finished and become much clearer.
- If the dissolved soap mixture is milky or very cloudy, it may need more cooking.
Dilute the Paste
If the test mixture stays clear as it cools, you can continue. The last measure of patience is needed when taking these steps to dilute the paste:
- Take the remaining 40 ounces of distilled water and bring it to a boil.
- Add the water to the soap paste. Stir it in a bit with a spoon or the potato masher.
- Turn the heat off on the slow cooker. Put the lid on and wait for about an hour.
- After an hour or so, stir the mixture some more. It should have softened a bit by now. It will likely be very chunky and gooey.
- Put the lid back on leave overnight to further dissolve, or continue to stir every hour or so.
Neutralize the Liquid Soap
After the soap paste has completely dissolved in the water, it's time to neutralize the soap and add your fragrance. Take the following steps:
- Turn the slow cooker back on and bring the mixture back up to 180 degrees Fahrenheit or so.
- In a separate container, mix the neutralizing solution. You can make either a 20 percent solution of boric acid or a 33 percent solution of 20 Mule Team Borax. For the boric acid, take 8 ounces of boiling water and add 2 ounces of boric acid. For the Borax, use 3 ounces Borax in 6 ounces of boiling water. It's important to stir well and make sure that the mixture stays hot. As this mixture cools, the Borax or boric acid will start to precipitate out of the mixture and it won't mix into your soap.
- Add about 3/4 of an ounce of neutralizer for every pound of soap paste (just the paste, not the added water.) For this recipe, which has about 2.8 pounds of paste, add 2 ounces of neutralizer solution. Using too much neutralizer (especially the boric acid solution) can cause cloudiness, so it's best to round down how much neutralizer you add by erring on the conservative side.
- Slowly pour the neutralizer into the re-heated soap mixture and stir well. Add one ounce first and let it sit for a bit. Then add another half ounce. If it remains clear and does not become cloudy, add the final half ounce.
Add Fragrance or Color
After neutralizing the soap, and while it's still hot, add fragrance and color. A good rule of thumb is to fragrance liquid soaps at about two percent to three percent. For example, this recipe will call for about three ounces of fragrance. Add the fragrance to the soap and stir it in well.
If adding color, put in a few drops at a time and stir well. Remember to take into consideration the amber color of the soap base while you're adding color.
Let the Liquid Soap Rest
It's time to let the soap cool. Pour the soap into large bottles or jars. Put the bottles or jars aside in a cool place to let the soap rest. During this resting phase, the insoluble particles should settle to the bottom and any minor cloudiness caused by insoluble particles in the oils or added fragrance oils should clear up. The soap will need to settle for one week. When you are pouring your soap into their final bottles or tubes, be extra careful not to disturb the settled solids.
Enjoy Your Homemade Liquid Soap
Congratulations, you've entered the advanced world of liquid soap making. There are nearly as many recipes and variations with liquid soaps as there are with bar soaps. Though there are no preservatives, homemade liquid soap potentially has a longer shelf life than bar soap because of the difference in oil content. However, different oils and techniques will result in varying products, from liquid soap to shampoo to shower gel.