A cautionary tale – I was afraid to make soap for a long time. I knew how caustic lye is and worried about having it in my house. Eventually, I gathered my courage and made a batch of soap. Several months later, while making another batch, I had a small accident: I had removed my gloves to blend the lye water and oils, and a tiny drop of unfinished soap landed on my finger without my noticing. After pouring the batch, I realized my finger was hurting. When I touched it, some skin sloughed off. That is how dangerous lye can be, so it’s very important to use the safety equipment listed below. Make sure every item you use is made of a non-reactive material such as stainless steel, glass, or plastic. Never use an aluminum pot; you will ruin both the pot and the batch of soap.
Equipment
Loaf mold
Scale
Stick blender
Stainless steel pot
Measuring cup
Bowl
2 thermometers or 1 no-contact thermometer
Gloves
Safety glasses
Optional – Spray bottle with 99% isopropyl alcohol and a pH meter
Materials
Various oils
Lye, also called NaOH – sodium hydroxide (not KOH – potassium hydroxide, also called potash, which is used to make liquid soap)
Distilled water
Optional – essential oil or fragrance oil
Recipe (the size of your mold creates a variable so I’ve listed ingredients by percentage; a soap calculator will calculate amounts after you enter the weight of oils)
Weight of oils that will fit in your mold
Lye concentration 33%
Super Fat 5%
Essential oil 0.7 oz per pound (if using a fragrance oil the oz per lb will vary but is usually printed on the label)
Shea Butter 5%
Olive Oil 44% (the soap may turn green or you can use a light or refined olive oil to keep the bar white)
Coconut Oil (76) 24%
Castor Oil 5%
Palm Oil 22% (sustainably produced)
Optional – I’ve made a list of additives below in Notes
Instructions
Use a soap calculator to determine the amount of lye and oils for your mold. I use this one: SoapCalc.
Put on gloves and safety glasses.
Weigh cold distilled water in a pitcher (cold water keeps the temperature lower when lye is added).
Weigh lye in a bowl.
In a well ventilated area or outside, slowly add lye to cold water (never add water to lye) and stir to dissolve. Turn your head away and don’t breathe in the fumes. Wait about an hour for the mixture to cool down, keeping track of the temperature with a thermometer.
Palm oil must be completely melted and stirred because it separates. Once melted, measure out the palm oil and add to a stainless steel pot.
Weigh out and add other oils to the pot.
Set the pot over medium-low heat and melt the oils together. When fully mixed, take off heat and track the temperature with a thermometer.
If you removed your safety glasses and gloves while weighing the oils, put them on. When both oils and lye water are under 110°F and within 10°F of each other, slowly combine them.
The hotter the lye water and oils are mixed the more likely the soap will go through gel phase. Gel phase is part of the saponification (the reaction between oil and lye to produce soap) process where the soap heats and turns translucent in the center. Sometimes the soap remains translucent, usually because the lye and oils were mixed at a higher temperature so the soap warmed to a higher temperature during gel phase. Gelled soap will only affect the look, not the quality, of the bars.
Use a stick blender to bring the mix to light trace (fully mixed but barely thickened) by mixing for a few minutes and letting it sit a few minutes.
Add essential oil (and fixative if using – see Notes) and continue to blend to medium trace (a thin pudding consistency). The essential oil may accelerate trace so be ready to pour.
Pour into soap mold and spritz top with isopropyl alcohol or cover the surface with parchment paper (this prevents soda ash, a reaction between the unsaponified lye and trace amounts of carbon dioxide in the air).
Wait 48 hours, then unmold and cut into bars if using a loaf mold.
Wait 4-6 weeks for soap to cure and harden. Optional – You can test the pH using a test pH meter; shave a gram of soap off a bar and dissolve it in 99 grams hot distilled water. It should test between 8 and 10 pH. If it tests too high, let it cure longer, a few weeks. If it still tests too high then you’ve made a mistake and there is unsaponified lye in your soap. If it is a good batch store in an airtight container.
Just for fun: The abbreviation pH is a unit of measure denoting the potential of hydrogen in an aqueous solution. A greater number of H⁺ indicates an acidic solution. A lesser number of H⁺ indicates a basic, or alkaline, solution.
Notes
Below I list common additives and the properties they lend to soap.
Cornstarch, arrowroot powder, or kaolin clay – a fragrance fixative; use 1/4 to 1/2 teaspoon per pound of oils
Sodium lactate or salt – hardens the soap faster; use 1% per weight of oils
Citric acid – extends the shelf-life; use 1% per weight of oils
Sugar – increases lather; use 1/2 to 1 teaspoon per pound of oils
I add the fixative at the same time I add the fragrance or essential oil – at thin trace. I add salt, citric acid, and sugar to the water just before I add the lye for safety, in case I splash some liquid. The lye will react with the water and heat it. Stirring it gently every so often will help the additives dissolve.
Soap calculators use the water content as a percentage of oils OR the lye concentration to determine the amount of water used. The water content as a percentage of oils is the amount of water added based on the amount of oils used. Many soap calculators will default to 38% percentage of oils. Lye concentration is the percentage of lye to water and I believe is the better way to determine the amount of water needed because it is based on the amount of lye used and not the amount of oils (different oils require different amounts of lye to saponify). A common lye concentration is 33%.
Superfat percentage is the amount of leftover oil in the soap and usually ranges from 1% to 10%. The reason you want leftover oils is so there is no chance of having leftover lye in your soap. The higher the percent of superfat the more moisturizing the bar will be. Too much leftover oil, however, will make the bar too soft and can cause the soap to go rancid faster.
