How to make liquid castile soap (uses potassium hydroxide lye)

Earlier this year I posted my recipe for making liquid soap from a bar of castile soap.  While I have been using that soap daily as a hand and dish soap and still like it, I have found it just does not compare to real liquid soap.  It works well for hand soap, but leave that soap residue and does not have the same cleaning power as my potassium hydroxide soap.  


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I use Dr. Bronner’s unscented castile soap in several of my home made recipes, and it has been my safety net since I had an allergic reaction to a body soap a couple years ago (after a full body allergic reaction to a scented soap I was afraid of pretty much any chemical in my body products, so I exclusively used Dr. Bronner’s as a hand soap and body wash for a couple months).  Now that I have successfully made bar soap, convincing myself that I am capable of working with caustic chemicals without burning myself, I decided it was time to give liquid hand soap a try.  My goal was to make a liquid castile soap that I could use interchangeably with Dr. Bronner’s unscented liquid castile soap.   So far I have used my liquid castile soap as a hand soap, face soap, dish soap, in my dishwasher, and in my laundry detergent.  As far as I can tell this soap cleans everything as well as Dr. Bronner’s, when diluted in the same way that I dilute Dr. Bronner’s (for reference, my face and hand soap is a 1:3 ratio of soap to water, dish soap is a 1:1 ratio of soap to water, and I use just 1-2 teaspoons in my dish washing machine (combined with a pre-wash and vinegar rinse – I’ll post that recipe later)).

All soap is made with lye.  Soap is made by the chemical reaction called saponification, during which lye dissolved in water (or another water-based liquid) reacts with oils.  Bar soap uses lye called sodium hydroxide (which is used as a drain cleaner and can be found in hardware stores).  Liquid soap uses potassium hydroxide as the lye (it’s harder to find; I bought mine on Amazon).  

When I decided I wanted to make my own Dr. Bronner’s equivalent soap, I decided to peruse the internet to see if anyone else had success, before taking the time to experiment with multiple batches of my own.  I was in luck, finding an awesome recipe from Erica on Northwest Edible Life.  Since I had the same desire for an end product as Erica, and after reading her post a couple times, I decided my first attempt at this liquid soap would be using Erica’s recipe.  I double-checked the ratios of ingredients using soapcalc.net’s soap calculator and got the same ingredient amounts (for reference, this recipe is 3% superfat, oil ratio is 60% olive, 40% coconut, and water as a % of oils is 80%) 

Liquid Castile Soap
Yields 1
Liquid castile soap comparable to Dr. Bronner's unscented liquid castile soap
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9925 calories
0 g
0 g
1134 g
0 g
486 g
2041 g
14 g
0 g
0 g
603 g
Nutrition Facts
Serving Size
2041g
Yields
1
Amount Per Serving
Calories 9925
Calories from Fat 9925
% Daily Value *
Total Fat 1134g
1745%
Saturated Fat 486g
2432%
Trans Fat 0g
Polyunsaturated Fat 80g
Monounsaturated Fat 523g
Cholesterol 0mg
0%
Sodium 14mg
1%
Total Carbohydrates 0g
0%
Dietary Fiber 0g
0%
Sugars 0g
Protein 0g
Vitamin A
0%
Vitamin C
0%
Calcium
3%
Iron
22%
* Percent Daily Values are based on a 2,000 calorie diet. Your Daily Values may be higher or lower depending on your calorie needs.
Ingredients
  1. 907.2 grams distilled water
  2. 265.0 grams potassium hydroxide 90%
  3. 680.4 grams olive oil
  4. 453.6 grams coconut oil
Tools
  1. Immersion blender
  2. heavy silicone spatula or wooden spoon
  3. large crock pot - at least 6 Qt, larger is better
Instructions
  1. 1. Measure the oils and pour into the crock pot. Turn the crock pot on high.
  2. 2. Measure the water (use room temperature or cooler) into your large mixing bowl and place in a deep sink.
  3. 3. Put on safety glasses, rubber gloves, and long sleeves/long pants and closed toed shoes to protect yourself from the lye. Carefully measure the potassium hydroxide, and slowly pour into the water. Stir gently so all of the potassium hydroxide dissolves. Note that this reaction is exothermic - it will produce heat - and the fumes are toxic. Do not breathe over the bowl and stand away as you stir.
  4. 4. Carefully pour the water-lye solution into the crock pot. Using an immersion blender, blend for 3-5 minutes, until the mixture is uniformly opaque.
  5. 5. Every 30 minutes or so, for the next 3 hours, blend the mixture to help thicken. If your mixture is too thick to use the immersion blender after your 30 or 60 minute check, turn the temperature to low (or warm if you're already on low). My crock pot is extremely hot, and it frothed a lot, the volume increased to fill the crock pot, and when I stirred I noticed that it began to gel in less than 1 hour.
  6. 6. Once the mixture is too thick to immersion blend, use your spatula to fold the mixture over itself. Keep folding every 30-60 minutes for 2-4 hours (or longer if needed), until the entire mixture is a uniform, translucent gelatinous mass.
  7. 7. Dilution. Once you have a saponified, gelatinous glob of soap, you need to dilute it to use it. Lower the crock pot temperature to warm. Add 6-10 cups of distilled water to your crock pot (ultimately you need 10 cups, but my crock pot only had space for 8), and gently stir/mash the soap into the water. If you're able, stir/mash every hour or so until the glob is fully dissolved. This should take 4-8 hours if you're stirring frequently. You may turn off the crock pot and let sit at room temperature overnight. Stir well in the morning and heat on warm if needed to finish dissolving.
  8. 8. Turn off the crock pot and allow the soap to cool to room temperature. Strain if desired, and pour into a clean 1 gallon vessel (I used my now empty distilled water bottle). If you have less than 1 gallon, add more water to fill the gallon bottle and gently swirl to uniformly mix the water and soap.
  9. 9. Use your castile soap as you would Dr. Bronners!
Notes
  1. 1. All measurements are by weight, not volume. This is required to ensure complete saponification. If your measurements are not precise you may end up with unsaponified lye, which can burn!
  2. 2. Use only sturdy glass, ceramic, or stainless steel containers, and heavy duty silicone or wood spoons (I prefer silicone). NEVER allow anything with lye to contact aluminum.
beta
calories
9925
fat
1134g
protein
0g
carbs
0g
more
My Greener Living https://www.mygreenerliving.com/
This recipe makes 1 gallon (128 fluid ounces or 3.785 liters) of liquid soap.

Ingredients

907.2 grams distilled water

265.0 grams potassium hydroxide 90%

680.4 grams olive oil

453.6 grams coconut oil

Tools

Immersion blender

heavy silicone spatula or wooden spoon

large crock pot – at least 6 Qt, larger is better

liquid castile soap
ingredients
Notes

1. All measurements are by weight, not volume.  This is required to ensure complete saponification.  If your measurements are not precise you may end up with unsaponified lye, which can burn!  If you don’t have a digital kitchen scale, I personally love and recommend this American Weigh Scales digital kitchen scale. 

2. Use only sturdy glass, ceramic, or stainless steel containers, and heavy duty silicone or wood spoons (I prefer silicone).  NEVER allow anything with lye to contact aluminum! (If you don’t believe me, watch this video of a potassium hydroxide-water solution or this video of a sodium-hydroxide-water solution dissolving aluminum foil)

Instructions
  1. Measure the oils and pour into the crock pot.  Turn the crock pot on high*. (*my crock pot runs very hot, so I went through this process using the low or warm settings.  If things are moving quickly you can reduce the heat.)
  2. Measure the water (use room temperature or cooler) into your large mixing bowl and place in a deep sink.
  3. Put on safety glasses, rubber gloves, and long sleeves/long pants and closed toed shoes to protect yourself from the lye.  Carefully measure the potassium hydroxide, and slowly pour into the water.  Stir gently so all of the potassium hydroxide dissolves.  Note that this reaction is exothermic – it will produce heat – and the fumes are toxic.  Do not breathe over the bowl and stand away as you stir. 

    liquid castile soap
    water with lye dissolving
  4. Carefully pour the water-lye solution into the crock pot.  Using an immersion blender, blend for 3-5 minutes, until the mixture is uniformly opaque.  

    liquid castile soap
    oils water and lye after blending
  5. Every 30 minutes or so, for the next 3 hours, blend the mixture to help thicken.  If your mixture is too thick to use the immersion blender after your 30 or 60 minute check, turn the temperature to low (or warm if you’re already on low).  My crock pot is extremely hot, and it frothed a lot, the volume increased to fill the crock pot, and when I stirred I noticed that it began to gel in less than 1 hour.
    liquid castile soap
    45 minutes after adding lye to oils. Thick and almost expanding out of the crock pot: a sign my crock pot was too hot.

    liquid castile soap
    Significant volume decrease after stirring. Only minutes after the last picture was taken,
  6. Once the mixture is too thick to immersion blend, use your spatula to fold the mixture over itself.  Keep folding every 30-60 minutes for 2-4 hours (or longer if needed), until the entire mixture is a uniform, translucent gelatinous mass.  

    liquid castile soap
    1, 2.5, 4.25, and 5 hours after mixing the lye and oils. My soap was sully saponified after 5.5 hours.
  7. Dilution.  Once you have a saponified, gelatinous glob of soap, you need to dilute it to use it.  Lower the crock pot temperature to warm.  Add 6-10 cups of distilled water to your crock pot (ultimately you need 10 cups, but my crock pot only had space for 8), and gently stir/mash the soap into the water.  If you’re able, stir/mash every hour or so until the glob is fully dissolved.  This should take 4-8 hours if you’re stirring frequently.  I let my soap sit overnight and stirred/mashed the remaining gelatinous blob in the morning.  Due to 8+ hours ignoring my soap, this process took about 14 hours. 

    liquid castile soap
    diluting the soap
  8. Turn off the crock pot and allow the soap to cool to room temperature.  Strain if desired, and pour into a clean 1 gallon vessel (I used my now empty distilled water bottle).  If you have less than 1 gallon, add more water to fill the gallon bottle and gently swirl to uniformly mix the water and soap.

    liquid castile soap
    finished soap ready to store
  9. Use your castile soap as you would Dr. Bronners!

    liquid castile soap
    finished product
Cost

Potassium hydroxide: $12.99 for 2 lb (907.2 grams).  (265g/907.2g)*$12.99=$3.70

Olive oil: $16 for 3L (2784 grams). (680.4g/2784g)*$16=$3.91

Coconut oil:  $14 for 54 fluid ounces (1530.87 grams). (453.6g/1530.87g)*$14=$4.15

Distilled water: $1 for 1 gallon (3,785.41 grams). (907.2g/3785.41g)x$1=$0.24

Total: $3.70+$3.91+$4.15+$0.24=$12/gallon

Dr. Bronner’s unscented liquid castile soap is $18 for a 32 oz bottle.  That’s $4 more for 1/4 the volume!