If you are familiar with making soap from scratch, you probably know that solid soap is made with sodium hydroxide and that liquid soap is made with potassium hydroxide (KOH). Potassium hydroxide is similar to sodium hydroxide, but makes soft soap, which combined with water, makes liquid soap. This guide will teach you how to make liquid soap from scratch, using potassium hydroxide.
Liquid Soap Ingredients
Combining a potassium hydroxide solution with various carrier oils and cosmetic butters makes liquid soap. Some carrier oils do better in liquid soap and some are best if left out or used in smaller quantities. Potassium hydroxide (KOH)
- KOH is the caustic substance used to turn skin-loving oils and butters into soap. Water
- Water is used to dissolve the caustic to make soap. Clear Liquid Oils
- Olive oil, rice bran oil, apricot kernel oil, sunflower oil, safflower oil, avocado oil, sweet almond oil, etc. are all wonderfully nourishing oils to use in liquid soap. A combination of these oils should makeup the bulk of a liquid soap formulation. All of these oils contribute to a clear liquid soap.Castor Oil
- Castor oil is great in liquid soap because it is also a solvent. This means that it can help with the clarity of your liquid soap.Coconut Oil
- Coconut oil adds bubbling and cleansing action to liquid soap. Coconut oil makes a clear liquid soap. Palm Oil & Cosmetic Butters
- Palm oil and cosmetic butters such as shea butter, cocoa butter, mango butter, etc. are great in liquid soap in smaller percentages. They tend to have higher amounts of stearic acid or other non-saponifiable material that can cloud liquid soap or contribute to sediment. Keep them to 3-7% of your formulation.
Additives in Liquid Soap
Both fragrance oils and essential oils can be used to scent liquid soap. Let’s discuss each:Fragrance Oils
- Fragrance oils are synthetic man-made aromatic ingredients that are used to scent soap and other products. Sometimes they can even contain natural essential oils. The typical usage rate is about 2% of diluted liquid soap.Essential Oils
- Essential oils are considered a natural way to fragrance your soap and are concentrated hydrophobic liquids containing volatile aroma compounds from plants. Essential oils are extracted from plant materials (flowers, bark, seeds, peel, roots, leaves, etc.) by expression, steam distillation or solvent extraction. The typical usage rate is about 2% of diluted liquid soap. Liquid Dyes
- are the best way to color liquid soaps. Colorants that color by particle suspension, such as mica, pigments, natural herbs and spice, etc. do not work well in liquid soap because the particles will just fall to the bottom of the liquid soap bottle. Dye Powders
- Dye powders are super concentrated colorants and are approved by the FD&C for use in soap.
Dye powders are best if premixed with distilled water. Add drop-by-drop using a dropper until you get your desired color. Using too much colorant in your soap can result in staining.
Liquid Soap Packaging
Liquid soap is best packaged into bottles with pumps or foamers. Foamer Bottles
- Foamer bottles are a popular way to package liquid soap. Foamers produce just that, a foam of soap. It is important to note that liquid soap used in foamers needs to be very watery. You can mix 1 part liquid soap paste with 2 parts water for dilution. (The standard is 1 part paste with 1 part water.)Bottles with Pumps
- There are numerous sizes and styles of bottles with pumps.
Using a Lye Calculator
Just as when making solid soap with sodium hydroxide, you will need to use a lye calculator to know how much potassium hydroxide is needed to make liquid soap based on your oils selected.
Wholesale Supplies Plus has a lye calculator, Click here
It is important to note that potassium hydroxide is only 90-95% pure. This means that when the lye calculator is set to 0% superfat, we still have 5-10% of unsaponified fats left in our liquid soap. This is important to note, because unsaponified fats can cloud liquid soap. To reduce cloudiness, we actually use a negative superfat with the lye calculator to reduce the amount of fat left unsaponified. -3% to -7% is the typical range to experiment with.
Using liquid glycerin in the dilution phase helps to add emoliency and a clear ‘superfat’ back into the soap.
You can play with using different superfats on the lye calculator and examine the results. In the sample recipe below, we use a -7% superfat in the lye calculator.
For liquid soap, ignore the water amount suggested by the calculator and simply use three times the potassium hydroxide to make a solution. You can see below in the sample recipe that we used 9 oz. of potassium hydroxide and 27 oz. of water. 9 x 3 = 27. This just keeps it simple.
Diluting Liquid Soap
Once your paste is made, you will need to dilute it to make a liquid soap. Liquid soap paste is comprised of the base oils and caustic solution (potassium hydroxide + water).
The amount of liquid you use to dilute is calculated based on your paste weight. You can use anywhere from 50-200%. In the recipe below, our paste total (add base oils, potassium hydroxide and solution water) is 78 oz. (100% dilution).
50% dilution rate = 39 oz.
100% dilution rate = 78 oz.
It is always a good rule of thumb to start low and raise the amount during dilution. You can always add more water, but it’s hard to take it out. In the recipe below, we go ahead and use 100%, but feel free to start at 75% and go up from there.
What can you dilute with?
Distilled water is most commonly used to dilute liquid soap. Liquid glycerin is another common liquid used. You can use varying percentages of your total dilution rate of each. You can use 50% water and 50% liquid glycerin. You can use 80% water and 20% liquid glycerin. This is what we use below.
Never use a liquid that is perishable, such as beer, wine, milk, vegetable juice, etc.
Keep careful notes and modify as needed for your next batch. If your soap is too runny, you can use less liquid at the dilution phase. If your soap is too thick, you can use more liquid during the dilution phase. Different base oils will require different amounts of dilution, so it really is trial and error based on your formulation.
How to Formulate a Basic Liquid Soap Recipe
Here is a great recipe for liquid soap if you don’t know where to start.
Coconut Oil - 10 oz.
Olive Oil - 10 oz.
Rice Bran Oil - 8 oz.
Avocado Oil - 8 oz.
Castor Oil - 6 oz.
Potassium Hydroxide - 9 oz.
Distilled Water - 27 oz.
Distilled Water - 62.4 oz.
Liquid Glycerin - 15.6 oz.
Essential or Fragrance Oil - 3.12 oz.
- Crockpot - A Crockpot or slow cooker is a great way to cook liquid soap.
- Immersion Blender - An immersion blender is what is used to mix the liquid soap to emulsion.
- Digital Scale - Liquid soap ingredients are measured by weight.
- Stirring Utensil - You will need a stainless steel spoon or silicone spatula.
- Stainless Steel Pot - To dilute your soap.
- Hair net and gloves
Potassium Hydroxide Safety
Potassium hydroxide is a caustic substance and can burn you. It can permanently damage eyesight if it splashes into your eyes. When using potassium hydroxide, wear safety gear including goggles, gloves and long sleeves. Have a copy of Potassium Hydroxide MSDS
on hand in case of emergency.
- If you get potassium hydroxide splashed on your skin, flush with water.
- If you get potassium hydroxide in your eye, flush with water and get to the emergency room.
- If you spill potassium hydroxide on a surface, spray with vinegar solution to neutralize, wipe up with towels, and launder as usual. Never use vinegar solution on potassium hydroxide on your skin or in your eye.
- Potassium hydroxide reacts with certain metals. Only use stainless steel when making soap.
Potassium hydroxide is used to turn the oils into soap. There is no potassium hydroxide left in the finished product.
Step 1: Weigh out the water needed for the caustic solution. Weight out the potassium hydroxide.
Step 2: Pour the potassium hydroxide into the water while stirring gently. Sometimes it will ‘hiss’ at you while it dissolves. Set aside to cool down.
Step 3: Weigh all of the oils into the Crockpot. You can melt any solid oils before putting them in the crockpot.
Step 4: Turn the Crockpot onto high and let the oils heat up.
Step 5: Pour the potassium hydroxide solution into the oils. Heat helps to emulsify the caustic solution with the oils, so you don’t need to let your solution cool down. As soon as the oils are all melted and the solution turns clear, you can mix.
Step 6: Stickblend to trace. Sometimes getting to trace with liquid soap can take awhile. Stickblend for about 10 minutes. Keep your Crockpot on high because heat helps. Walk away for about 10 minutes. Come back and stickblend some more and you should get to trace. If you still aren’t there. Walk away again for 10 minutes and come back to try again. You’ll get there eventually. Don’t stress, because it will all come together. Some liquid soap formulas are quick and some take a long time to trace.
Step 7: Put the lid on the Crockpot and let cook for about 30 minutes. Don’t stir. The soap will get puffy and rise a bit. Some of it will turn translucent.
Step 8: After 30 minutes, stir really well.
Step 9: Let cook for another hour or so until most of the soap has turned translucent. It helps to not stir, because then you can see which soap has turned translucent and which hasn’t.
Step 10: Boil 62.4 oz. of water and 15.6 oz. of liquid glycerin in a stainless steel stockpot.
Step 11: Spoon liquid soap paste into the pot. Turn off heat, cover tightly and let sit. Dilution takes hours. As you walk by the pot, stir every now and then. When it cools off, turn the burner onto med and heat it up again. Stir. Turn off. Allow the mixture to sit. It takes time for the liquid soap paste to absorb all of the water. Start dilution at night so it can sit overnight to do most of the work. Time and heat are your friends during the dilution phase.
Step 12: Once diluted, you can add scent. You can scent the whole batch or you can divide out into different scents. Scent is added at 2% of liquid soap base. Weigh out the soap that you want to scent, multiply by 0.02 and that is the amount of scent you will use.
Important note: Fragrances and essential oils effect liquid soap in different ways. Sometimes they can thicken liquid soap, they can loosen liquid soap, they can cloud liquid soap…etc. ALWAYS test a fragrance oil or essential oil prior to scenting a large amount of soap. To test, weight out 200 grams of liquid soap. Add 4 grams of scent and see what happens. Allow it to sit overnight and examine the next day.
Step 13: Bottle and enjoy!