Liquid Castile Soap Making – 100% Olive Oil Liquid Soap Recipe
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My enjoyment of liquid soap making deepens all the time. It’s been a long, slow learning process, but worth every minute. This recipe is a simple yet elegant one. It has only four ingredients, but makes the most perfect, gentle liquid soap.
If you’ve seen my older bar soap recipes on YouTube, you’ll know I’m a lover of olive oil based soaps. It is the queen of soap making oils! It makes a very gentle soap that keeps well and is perfect for handwashing.
There’s a lot to learn in the realm of soap making and liquid soap making is no exception. The book Liquid Soapmaking (ad link) by Jackie Thompson, has been an invaluable resource for me, and while I use a different method than Jackie’s to calculate my recipes (explained and demonstrated in this video) I’ve learned a lot from her work and am very grateful for her experience and scholarship.
As always, if you are new to soap making - make sure you check out my introductory material for beginners, and watch this important video about lye safety which helps to build knowledge and confidence as a beginner soap maker. Soap making is serious business and it’s important that you fully understand what is involved.
I hope you enjoy this recipe. It would be a great one to try for a first attempt at liquid soap making!
Liquid Castile Soap – 100% Olive Oil Liquid Soap Recipe
Please ensure you are familiar with the basics of soap making including safety requirements before you attempt this or any handmade soap recipe. Please view my soap making safety video here and read my disclaimer here.
This recipe uses the paste method for liquid soap making whereby an initial soap paste is made and completely saponified (turned to soap) before dilution for use in pump bottles or other containers.
Soap Paste Ingredients
500g olive oil
I have noticed that my liquid soap is thicker if I use extra virgin olive oil. I have to do some more rigorous testing to see if this is truly the case, but it seems to be! Any type of olive oil will work for this recipe, I used semi-refined olive oil for the video.156g water
Distilled or demineralised water is best (makes the clearest soap), but filtered, sanitised drinking water is also fine if it is a soft water type.104g potassium hydroxide (KOH)
Mine is 90% purity. If you have a different strength, you’ll need to recalculate this recipe. This video shows you how I do it.104g vegetable glycerine
This is an optional ingredient. If you don’t have glycerine you can replace it with another 104g water.
*Be aware that glycerine acts as a solvent in this recipe and does wonders to accelerate saponification and prevent separation of oils and lye water as the soap paste is mixed and cooked. This recipe requires a lot more patience and stick blending without the glycerine, but it can be done! Glycerine also adds emollience and extra moisture to the recipe due to its humectant properties, so it’s great to use if you have it.
Dilution water
You will need between 1700g (1.7 litres) and 2100g (2.1 litres) of distilled, demineralised or filtered tap water to dilute this full soap paste recipe. Start with 1700g and add more if needed (see video for discussion/demonstration). Note that if you use filtered tap water, your soap may not be perfectly translucent due to minerals in the water.
You can also dilute just a portion of this soap paste and store the remaining paste in the fridge for later dilution as I do in this video. Start with a dilution ratio of 1 part paste to 1.5 parts water (by weight) and add more water if needed.
Other recipe specifications
The crock pot I used in the video is a small one, it holds 3 litres. If you don’t have a crock pot you can make this soap using a saucepan on the stove on very low heat, or use a double boiler.
This recipe is made with a 1% superfat, and does not require any additional ingredients to adjust the pH of the soap. See this video about my method for calculating liquid soap recipes for more details and rationale.
This recipe is calculated with a 1.5 : 1 water to lye ratio for the paste, however with the additional glycerine added (or water if you have no glycerine), the final water to lye ratio becomes 2.5 : 1.
My potassium hydroxide is 90% purity and the recipe is calculated to factor that in.
The recipe makes approximately 840g of soap paste and 2.7 litres of finished liquid soap. Your yield may be slightly more or less than mine, depending on evaporation during the cook.
Salt solution for thickening
This is completely optional (I did not use any salt to thicken my soap in the video demonstration) but olive oil based liquid castile soap lends itself quite well to thickening with a 20% salt solution.
If you are using essential oils (see below) make sure you add those before you thicken the soap with a salt solution. Many essential oils thicken liquid soap by themselves, in which case further thickening with salt is not required.
To make the salt solution, mix 20g of non-iodised table salt with 80g of distilled (or otherwise purified) water and stir until fully dissolved.
Add the salt solution to completely cooled and diluted liquid soap, in small amounts (a teaspoon or less to start with), stir thoroughly and leave the soap to thicken for 30-60 minutes before checking. Be careful not to add too much, only slight thickening is recommended. Too much salt can inhibit the lather and will not thicken the soap beyond a certain point. Jackie Thompson in her book Liquid Soap Making (ad link) recommends adding no more than 1% salt solution of the total diluted soap amount (for example, if you have 500g of diluted liquid soap, you would add no more than 5g of 20% salt solution).
Essential oils
I did not add any essential oils to my Liquid Castile Soap in the video demonstration, however I usually add essential oils as I decant this soap into individual bottles to use around my household.
I like to use 1-2% essential oils in my finished liquid soap. To calculate this I multiply the weight of the diluted soap (in grams) by 0.01 (1%), 0.015 (1.5%) or 0.02 (2%) to get the amount of essential oil needed, in grams.
If you would like to fragrance your liquid soap using synthetic fragrance oils, check the manufacturer’s suggested usage rates. If you aren’t sure I would start at 0.5-1% for fragrance oils. A little goes a long way in liquid soap!
Be aware that some essential oils and fragrance oils can dramatically change the texture of liquid soap - some will thicken the soap, some will make it runny. Experiment with small amounts first to see how your oils react with your soap.
METHOD
*Please view the video for the full tutorial before you start.
Weigh the olive oil into your crock pot or slow cooker. Turn the cooker up to high to heat the oil. The soap will come together quite easily if the temperature is warm enough. Between 75°C/167°F and 80°C/176°F is ideal. If you do use the high temperature setting to heat your oil up faster (as I do), make sure you watch it closely and turn the cooker down to the low or ‘keep warm’ setting before it gets too hot. 85°C/185°F is the absolute maximum temperature for liquid soap making. Too much hotter and the soap will expand/volcano and will over-oxidise.
Wearing gloves and goggles for safety, weigh the potassium hydroxide into a small container, cover with a lid and set aside.
In a medium sized jug, weigh water for the lye solution and when you are ready (with your gloves and goggles on, and a mask if you are in an unventilated area) slowly pour the potassium hydroxide into the water, stirring to dissolve. Set aside somewhere safe.
Weigh the glycerine into a small bowl and set aside.
Get your stick blender ready and pour the dissolved lye solution into the warming oil. Start stirring and blending. Be very careful to keep the blades of your blender under the soap surface to avoid splashing. KEEP YOUR SAFETY GOGGLES ON THROUGH THIS ENTIRE PROCESS.
Add the glycerine soon after mixing the lye solution into the oils.
Keep an eye on the temperature (see point 1) and stick blend your soap batter off and on between manual stirring, to give your blender a rest, for about 10 minutes or until it thickens to a uniform, thick pudding consistency (see video).
Cover the soap, turn your cooker down to low or ‘keep warm’ and leave it to cook for 30 minutes or until it becomes glossy and translucent.
Test the soap paste with pH paper (ad link) and check it with a clarity test, as demonstrated in the video. If the soap is cooked and fully saponified, no lye remains and the soap paste is ready to dilute.
Weigh the dilution water. Start with approximately two times the weight of the paste and add more later if needed.
Add dilution water to the soap pot, cover and let it sit for a few hours on low heat. You can stick blend the soap as I did in the video once it is at least half diluted. This helps it along in the final phase of the dilution.
Once your soap is diluted and cooled down, if you see a skin forming on the top of the soap, more dilution water is needed. Add more water in small amounts until the soap no longer skins.
Cool the soap, add essential oils if desired, and pour into bottles for storage or immediate use around the house. A lot of liquid soap makers suggest sequestering the soap for a couple of weeks before use, however I never do this. As long as the soap is fully saponified (and the pH is tested properly) then I am happy using my liquid soap straight away.
What about preservatives?
I make my liquid soap for personal use around our household and do not use a preservative for my relatively small batches. This is a great article on the topic of whether or not to use a preservative in your liquid soap. Because I have never used a preservative, I cannot offer you any educated guidance on the topic. Make sure you do your own thorough research in this area, especially if you are giving or selling your liquid soap to others.
Well, that’s it for now!
I hope you enjoy this recipe as much as I do.
Please leave a comment below if you have any feedback or questions.
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