Easy, Beginner DIY Liquid Castile Soap Recipe
Made with only olive oil, this pure liquid Castile soap is easy to make and mild. It’s perfect for face and body, and for cleaning around the house.
A couple of years ago, I showed you how easy it was to make a basic beginner soap, even if you’ve never done it before.
Making solid soaps can be a lot of fun, but not everybody likes using bar soap. Many people prefer using something in a dispenser like a shower gel or a liquid soap.
I made many different types of bar soaps before attempting to make a true liquid soap. There aren’t as many resources about making liquid soaps, so I had to do a lot of trial and error before posting this first liquid Castile soap recipe.
Once you find a good recipe, it’s pretty simple to make. While it does take a little more time and effort than whipping up some bars of cold process soap, I think you’ll find that it’s well worth it, especially when you take a look at the price of a store-bought liquid castile soap.
How does liquid soap differ from bar soap?
The main difference between bar soaps and liquid soaps is the type of lye used to make them. Liquid soaps are made with KOH, or potassium hydroxide, rather than NaOH, or sodium hydroxide.
You can read more about the different types of lye in my post about lye and why it is needed in soap.
While some people like to make a “liquid soap” of sorts by diluting bar soaps in water, you can’t really get a true, transparent liquid soap that way. Some people are happy with the result, but every time I’ve tried it, I’ve ended up with a gloopy mess. It doesn’t have the same cleaning power as either a bar soap or a true liquid soap, and the texture and appearance aren’t the same either.
What is pure Castile soap?
Technically, by definition, Castile soap is a type of soap made with only olive oil. The name “Castile” soap originates here in Spain. (You can read more about the origin of Castile soap and other soaps in my post with a recipe for pure Castile bar soap.)
Over the years, the definition of Castile soap has broadened to include other types of vegetable oils such as coconut oil. Dr. Bronner’s liquid Soap, which may be the most famous commercial liquid Castile soap, actually has a greater percentage of coconut oil than olive oil. (I made a Dr. Bronners liquid Castile soap copycat recipe for those who are interested!)
When it came to making a homemade liquid Castile soap, though, I was a bit of a purist and made the real deal: a soap made with only olive oil.
Olive oil in soap
Soaps made with different oils have different properties.
Soaps made with olive oil are more conditioning for your skin than soaps made with coconut oil. On the other hand, they don’t lather up as much as a coconut oil soap, nor do they leave you feeling squeaky clean in the same way (partly because they are more conditioning).
Some people find pure Castile bar soap to be “slimy” and not cleansing enough. On the other hand, pure coconut oil bar soap can be drying.
- Pure coconut oil soaps are great for general cleaning and for laundry. That’s why I made my homemade laundry soap only with coconut oil.
- Pure olive oil soaps tend to be gentle on the skin and great for gentle body cleansing.
Read my post about the properties of different oils in soaps.
Ideally, you’d combine different oils to get the qualities you want for your soap. That’s exactly what they did when they formulated Dr. Bronner’s soap, and what I did when I showed you how to make a basic beginner soap which uses a combination of olive oil and coconut oil.
Combining liquid soaps
When you make a bar of soap, you have to decide what combination of oils you want to use from the very beginning and your entire batch will have that very same combination.
With liquid soaps, though, you have the advantage of being able to combine your various soaps after the fact, making it easier to experiment with smaller combinations until you find the perfect soap for your need.
That’s why I made a pure liquid castile soap, using only olive oil, and then later made a pure liquid coconut oil soap. Once you’ve made both of them, you can combine them, as needed to get the type of soap you want.
Coconut oil liquid soap vs. liquid Castile soap
When I first started making liquid soap, I assumed that liquid soaps would be just like bar soaps. The difference between a pure Castile bar soap and a coconut oil-based bar soap is HUGE!
I was very surprised to find, though, that liquid soap made with coconut oil was actually quite similar to that made with olive oil. Sure, the olive oil-based liquid soap was darker in color than the coconut oil-based liquid soap. For me, that was probably the most notable difference.
Yes, the coconut oil soap does make a bubblier lather than this one and may be slightly more drying. It does give more of a “squeaky clean” feeling.
In the end, though, the difference isn’t as pronounced as I expected. In fact, I normally just make the coconut oil liquid soap recipe these days. I can buy refined coconut oil cheaper than olive oil, but also love the look of a lighter-colored soap. I also love the fresh, subtle scent of the coconut oil soap when left unscented.
Both soaps give a decent lather. They are also both relatively mild for skin. If you have sensitive skin, though, this soap is probably the better choice.
Those who have very sensitive skin may find that they have issues with the higher pH of any soap. In those cases, it may be best to use something like my DIY Baby Wash and Shampoo. (I made it pH balanced for a baby’s delicate skin.)
Ingredients
This soap uses 4 main ingredients: olive oil, potassium hydroxide, water, and glycerin.
You can use extra virgin olive oil or a lighter olive oil. What is important, though, is that you are using pure olive oil. (If it’s not pure olive oil, it may need a different amount of lye.)
For the water, it’s best to use distilled water. Tap water has minerals and may have other impurities that can affect the clarity of your soap.
Why use glycerin when making liquid soap?
One of the methods of making liquid soaps is called the glycerin method. It replaces part of the water with glycerin.
Adding glycerin moves the soap-making process along more quickly. Because I wanted to share a beginner liquid soap recipe, I chose the glycerin method to have this soap be as quick and fool-proof as possible.
Using glycerin may have some other benefits:
- The resulting soap paste dissolves very easily in water. I don’t need to heat the water nor do I need to leave it for days at a time. I can cover my soap paste with distilled water and usually, in a couple of hours, I have a beautiful, clear liquid soap effortlessly.
- Glycerin is a humectant, meaning it draws moisture into the skin. I find that even my liquid coconut oil soap doesn’t feel drying, despite the fact that it hasn’t been superfatted at all. I think the extra glycerin helps to make a really great, hydrating soap that is clear and doesn’t need extra oils. (I think my homemade glycerin bar soap has the same benefits.)
Materials
To make liquid Castile soap, you only need a few basic tools. An immersion blender helps mix the oils and lye solution quickly so the soap reaches trace faster. A slow cooker works beautifully for keeping the soap at a steady, gentle heat while it cooks. A kitchen scale is also important here, since soap making relies on accuracy. Measuring by weight instead of volume helps ensure that your recipe turns out perfectly every time.
Procedure
Making a liquid Castile soap isn’t difficult and it can save you a lot of money.
To get the clearest soap we can, we’ll use a hot-process method. That means that we will be cooking the soap. During the cooking process, the saponification process will complete and our soap will be ready to use immediately afterwards. (Liquid soap doesn’t need a curing time in the same way as bar soap does.)
The easiest way to make this and have it come out perfectly is to use a slow cooker. If you don’t have access to a slow cooker, though, you can also try baking it in the oven. (I showed how I used this method in the post and video for the coconut oil liquid soap.)
Making the lye solution
Weigh out the glycerine, water, and potassium hydroxide (KOH).
Add the glycerin to the water and then carefully add the KOH to the water and glycerin mixture. (Not the other way around!) Make the lye solution in a well-ventilated area.
Stir the KOH into the water until it dissolves. It will be cloudy at first, but then it will clear up.
Making the soap paste
Measure out the olive oil and heat it over low heat directly in the slow cooker.
Slowly add in the the KOH mixture to the warm olive oil, and gently stir them together over low heat.
Once combined, use an immersion blender to blend the ingredients together in the slow cooker. In a few minutes the mixture will begin to thicken and look like mayonnaise. Soon after, it will look like a creamy pudding. (If you aren’t doing this over heat, it will take a bit longer.)
A few minutes later, the mixture will begin to look grainy and look like mashed potatoes or applesauce. Continue to blend.
If, at any point, the mixture becomes too thick to blend with the immersion blender, switch to mixing with a spatula or wooden spoon. It’s also a good idea to take breaks during the blending process so as not to burn out the blender.
As you continue to blend, it will start to get creamy again. It is now time to cover it and cook it for a while.
Cooking the soap paste
Cooking the soap paste will allow the soap to finish the saponification process and will also help achieve a perfectly clear liquid soap immediately. The process will take 3-4 hours, and you will want to check on it and stir it up every half an hour or so.
As you cook the mixture, it will begin to thicken up and become more translucent.
To check for “doneness,” we will look to see if our paste is dissolving into a completely clear liquid soap. To do this, take a small amount of the soap paste and dissolve it in water, and look to see if the water is clear once the soap paste is dissolved.
If the liquid is cloudy, you should continue to cook the soap in the slow cooker. Let it cook another half an hour before checking on it again. If it dissolves clear like the soap in my picture, you are finished making the soap paste.
Note: If you aren’t using distilled water, the soap paste may stay cloudy no matter how long you cook it! (For more reasons your soap paste may be cloudy, read my post about troubleshooting liquid soap problems.
How to dilute the soap paste
Once you have made your soap paste, you’ll need to dilute it to obtain a liquid Castile soap.
To dilute a soap paste you can:
- Let it dissolve by itself into water over the course of several hours (or overnight).
- Speed up the process by warming the water and soap paste over the stove or other heat source (like the slow cooker).
For clear soap, use distilled water. That will also help ensure the water is free of contaminants and the soap will keep as long as possible. By choosing distilled water, not only are you keeping the possibility of microbial contamination to a minimum, but you are also ensuring that minerals and other substances in your tap water won’t cloud your soap.
If you are making small batches that are going to be used relatively quickly (and aren’t concerned about clearness), you can probably get away with tap water without any issues. I still recommend using distilled water when possible.
Read more about how to dilute a soap paste here.
Customizing your liquid soap
How else can you personalize your soap?
Adding fragrances
Unlike with bar soap, you can add in additives like essential oils after the fact. So, you don’t have to divide your batch at trace and work quickly to make soaps with a variety of fragrances. Instead, you can make a large batch of concentrated liquid soap paste base. The soap paste can be stored away and keeps well for a very long time. (I’ve successfully stored soap pastes for several years without issues.)
You can then add in the essential oils or fragrance oils as you dilute the soap paste. This gives you the freedom, even months after making the soap, to play with fun combinations.
At the time of dilution, I mix the soap paste with distilled water and then I add essential oils to give my soap a personalized fragrance.
Does it need a preservative?
Whether or not liquid soap needs a preservative is a controversial subject. Personally, I don’t use one as the pH of soap is high enough that it’s not a favorable environment for the growth of most of the microbes that we’re trying to avoid.
If I were going to sell a liquid soap, though, I’d do proper microbial testing of the liquid soap to see if a preservative was needed or not. Most natural preservatives on the market aren’t effective at the high pH of soap anyway. (Euxyl® K 900 is an exception and would be a great preservative to consider for using in soap.)
For more liquid soap FAQ’s, read my post How to Make a Liquid Soap: Start Here.
Video
Easy liquid castile soap (made from scratch with olive oil)
Materials
Instructions
- Measure out the olive oil and add it to the slow cooker on low heat.
Make the lye solution
- Weigh out the glycerine, water, and potassium hydroxide (KOH).
- Mix the water and glycerin.
- Carefully add the KOH to the water and glycerin mixture. (Not the other way around!) Do this step in a well ventilated area.
- Stir the KOH into the water until it dissolves. It will be cloudy at first, but then it will clear up.
Make the soap paste
- Slowly add in the the KOH mixture to the warm olive oil, and gently stir them together in the slow cooker.
- Once they are mixed together well, use an immersion blender to blend the ingredients together. In a few minutes the mixture will begin to thicken and look like mayonnaise. It will later look like a creamy pudding.
- The mixture will go through stages, from creamy to grainy and back to smooth.
- As you continue to blend, it will start to get creamy again. Once you reach this point, you can stop blending with the hand held blender and can leave the soap paste cooking covered in the slow cooker.
Cook the soap paste
- As you cook the soap, it will continue to thicken and will become more translucent. To achieve a clear liquid soap we'll need to cook the soap paste for 3-4 hours. During that time, check on it and stir it up every half an hour or so.
Check for doneness
- To check for "doneness," we will look to see if the soap paste dissolves clear. To do this, take a small amount of the soap paste and dissolve it in distilled water. If the resulting soap is clear, the soap is finished cooking. If it's cloudy, continue to cook the soap paste for another half an hour before checking on it again.
Dilute the soap
- To make a liquid Castile soap, dissolve some of the paste in distilled water. I ususally use a ratio of one part soap paste to 2-3 parts distilled water. Let it sit until dissolved, or gently heat to speed it up.
Notes
- A slow cooker is perfect for this because it gently heats without burning and keeps everything at a steady temperature. If you don’t have a slow cooker, you can bake the paste in the oven or cook it in a double boiler.
- Take breaks while blending so you don’t burn out the motor of your immersion blender. If your blender gets too hot, you can pause and let it cook before continuing.
- If the mixture becomes too thick to blend at any point, switch to mixing with a wooden spoon.
- If you’ve cooked it for more than 3–4 hours and it still isn’t clear, there may be other issues. Tap water can cause cloudiness. For other possibilities, see my post on troubleshooting liquid soaps.
- This recipe makes about 4.5–5 pounds of soap paste, which can be diluted to 10–20 pounds of liquid soap or more, depending on how concentrated you want it. That’s roughly 1–2 gallons or more.
- Keep in mind that liquid soap is not as thick as commercial gels or surfactants. It has a thinner consistency and doesn’t need to be thick to be concentrated and work well.
- Undiluted soap paste can be stored in glass or plastic containers in a cool, dry place for more than a year. I’ve had some last for several years without any problems. It may eventually develop a slightly rancid smell, but can still be used for general cleaning.
DIY liquid body soap recipe:
If you would like to combine this soap with a liquid coconut oil soap to obtain a bit more lather and a squeaky clean feeling, try using this ratio:
60-70% liquid Castile soap (made with only olive oil)
30-40% liquid coconut oil soap (for bubbly lather, link goes to the recipe post)
Essential oils of choice.
Mix all of the ingredients together, and keep a bottle in the shower to use instead of shower gel.
Add essential oils for fragrance. Lavender essential oil gives a lovely herbal scent. I also like citrus blends using lemon and bergamot.
What are your favorites?
This post was originally published on June 29, 2016. It was rewritten and republished in June of 2021, adding new information, more photos, and video.
This is a lovely article. However I would love people reading to know that the origin of (cake) olive oil soap (& the invention of soap in sum) is Syria (Syria / Lebanon / Palestine) – not Spain as you have written.
After it began to be produced in Spain much later it became known in England etc. as Castile soap; as it was produced there for much of Europe.
One can research Nablus (Palestine) soap & Tripoli (Lebanon) soap & Aleppo (Syria) soap. All of them still made. (Although war & occupation have affected their production).
This may seem a small matter – but since we are maligned at every turn inc. frequently called ‘greasy’ / ‘dirty’ / ‘backward’ etc. – people should know that we invented soap & it is still made the same way there.
The Bedouin supplied the sodium ash from a plant grown along the river. My family comes from ancient olivers (olive vineyard owners) & priests in South Lebanon. (Priests were landowners). Many things were brought to Spain & Europe from Syrians & Arabs. (glass / parfum / soap / underclothes – underwear / stone building techniques etc.). Arabs & Syrians were in Spain for 800 years. And also Portugal & the South of Italy.
Thank you for allowing me to write slightly off topic from soap production technique here ??????
Hi Hayet,
I’ll have to take a look at what I wrote in this post and edit it as needed.
I actually wrote about the origin of Castile soap in my pure Castile soap recipe. You’ll probably like my description of the origin better there. I think that I probably was meaning that in Spain they tended to stick to soaps made with only olive oil, whereas in other regions the soap took on different names and used different oils. In your area laurel berry oil is commonly used with the olive oil and it’s marketed as Aleppo soap and not Castile soap (which goes back to the definition you use for Castile soap), in France they tend to use a different combination of oils (including olive oil), and it’s marketed as Marseille soap. They are all very similar in nature, though, and some (probably most) people will call all of them Castile soaps nowadays.
I also have a laurel berry soap recipe on the blog just to pay tribute to the way the Aleppo soaps are made. I occasionally buy Aleppo soaps, despite making a lot of soap myself, because I happen to love it. I definitely don’t want to take credit away from where credit is due. I’ve watched the videos of how Aleppo soap is made, and truly am inspired by their workmanship. 🙂
Is this tear free? If not how could I make it tear free to use for a baby.
Hi Rachel,
From what I understand, tear-free formulas really only have a pH that is closer to the pH of your eyes. That’s closer to the neutral range of 7, but may be around 7-8. The pH of soap is normally higher than that.
Most tear-free shampoos are surfactant based. For a baby you could use a gentle surfactant like the one I used in my micellar water, and then test the pH to get it into whatever range is most important to you. (Skin pH tends to be more acidic and lower.)
You can try to bring down the pH of soaps slightly with citric acid or something, but too much and the soap will fall apart. Soap always has a more alkaline pH.
Many people use Castile soaps on babies- you just have to be careful around their eyes, but in reality probably any product will irritate eyes to a certain extent.
Hi. I have been making solid soap with no apparent problem until I tried making liquid soap yesterday and it separated into 2 layers. Clear on the bottom and paste like on the top. Can I do something to save it ? Cook it? More blending? Or I really should throw it out? Thankss .
Hi Dewi,
I definitely wouldn’t toss it.
Yes, you can try cooking it more, but in my experience with a bit of time, pastes that haven’t fully cooked actually go through and finish the process on their own with time. It may be that by now it’s already fixed itself? When you say clear on the bottom, what do you mean? Is it liquid?
If you are able to mix it all, that’s what I would do. I would then either try cooking it for longer or just set it aside in a large glass jar to see what happens over the next few days. Test out a small amount of the mixture by dissolving it in water and seeing if it behaves like soap.
Thank you for providing me with exactly what I was looking for! I cannot find a soap (liquid or otherwise) that does not have an excess of drying ingredients it. I will need to make it. I have no trouble with the soap being thin except for one problem: thin soap does not stay in the hand very well. During my research, I came across guar gum. Apparently, this is a common thickener for commercial soaps. It is also natural. I may try it for thickening and see how it comes out. when I do, I will report back.
Hi Denise,
I haven’t tried with guar gum with soap yet. I have tried guar and/or xanthum gum with gels and lotions and things to different levels of success (or not). 😉
I’ve often had big blobs of gum in the bottom, and other not-so-great results, but I don’t usually mix very well because I’m afraid to make a lot of foam.
In the end, my favorite way to dispense liquid soap that is thin is to use the foaming dispensers. Those are great and make for a fun product that is easy to use.
I’d really love to hear how your experiments go, though!
Hello! I am just trying this, and it won’t make it to, much less past, the step 5 creamy pudding consistency. I used an immersion blender until it was so hot I couldn’t hold it (10 min?), a hand mixer for about 5 min, then stirred by hand for about 30 min. I read a bunch of the over comments while stirring ?, and it looks like it will be as safe and effective now as it would be if I progressed through the steps, it’s just unlikely to be transparent. It’s that accurate? I’m about to leave it cooking on low for a few hours, just in case there’s any value… Thank you!
Hi Hope,
I think that, yes, it will be fine. If you didn’t cook it for several hours, you may not have gotten through all of the stages, but they are mostly there for you to make a mostly transparent soap. Whether or not it’s immediately transparent is hard to know. My best guess is that over time it will become transparent on it’s own.
In either case, that’s a cosmetic issue, so it shouldn’t be an issue for safely using your soap. 🙂
Thank you! As it turns out, though the blending and stirring didn’t help it progress through the stages, as you noted in your reply, it did progress just from cooking on low for several hours. And, it does seem to be transparent! That was not even a big deal for me, but glad it worked. Thanks so much for sharing this recipe. I’ll be trying the coconut oil one next! ?
Hi! First off, I’m new to soap making, so I don’t really know much about the effects of different oils and such! However, I always try to source locally whenever I can and avoid plastic and the like- which is why I was wondering if rapeseed oil would work in castile soap? It is one of the only oils available locally grown and pressed near me. Thanks in advance!
Hi Jess,
Yes, you can use rapeseed oil. It’s a more conditioning oil in soap, but shouldn’t be used in large percentages because it can go rancid or cause the soap to get ugly brown spots. To make a more cleansing, stable bar, you’d want to add a solid oil like coconut or lard or tallow, or butters and such. I can’t readily find rapeseed oil here in Spain because nobody ever uses it. I specially bought some to try to do a copycat recipe of the Beautycounter charcoal face bar. You can see my recipe for an activated charcoal soap here as an example soap with rapeseed. I also used it in my dog shampoo bar.
If you want to modify the oils in a recipe, you have to run it through a lye calculator first to check how much lye will be needed for the new recipe as not oils need the same amount of lye.
Hi Tracy,
I hope you are doing fine. I really need your help more, more than you imagine. I was applying your amazing recipe for a project, however, I couldn’t come to step 6. The soap hardened like tiny pieces of mashed potatoes and did not look creamy eventually. I stopped cooking it because it kept hardening. I wish you could give me an advice so that I can make it creamy to proceed with my project. Thank you in advance.
Hi George,
Did you use KOH (potassium hydroxide) as your lye? (That’s my first question because using NaOH lye will result in a solid bar and not a paste for a liquid soap.)
After that, it’s hard to know what’s going on without seeing a picture. You could send me one at [email protected], and I can try to help.
You may be just fine- the past doesn’t always necessarily turn out exactly the same.
You could dilute some of it to see how it behaves. (Ideally it would be interesting to know the final pH of your diluted soap to get a better idea of what’s up.)
Oops – also, does the olive oil need to be extra virgin or is it better if its not?
Hi Liz,
I usually use extra virgin olive oil, but that’s because I usually buy a good extra virgin olive oil here in bulk, so I almost always have a lot of it at home. I can buy it for a very good price here in Spain. That said, it doesn’t really need to be extra virgin olive oil. What is more important is that it be pure olive oil and not olive oil mixed with some other oil. That could really throw off a soap recipe.
As for the storage of the finished soap paste- I usually use glass jars. I prefer to avoid plastic whenever I can, so that’s why I choose glass, but you can use plastic. What I would avoid, though, is any sort of metal container. I ruined one of my soap pastes because I didn’t realize that the tin I was storing it in wasn’t stainless steel. Stainless steel should theoretically be OK, but I’ve had the paste react with metals so I try to avoid any sort of metal just in case. (I do use stainless steel liquid soap dispensers at times, though. I think it must be the concentration, the fact that the soap paste is freshly made, and that it is stored for so long that can cause the problems.
I usually keep mine on top of the medicine cabinet in a bathroom that we don’t use very often, so it doesn’t get a lot of light, but to be honest with you, I’m not sure how much the light would affect it. I guess I always try to store anything I’ll be keeping for a long time away from the light, just in case.
Hi, before I start this, could you tell me what you store your undissolved liquid soap in? Does it need to be glass or dark glass or does it matter? Thanks.
would love to try if I only knew thar KOH is???? and NaOH????
KOH (potassium hydroxide) and NAOH (sodium hydroxide) are the types of lye used most in making soaps. NaOH is the lye that can be commonly found in the drain cleaning section of supermarkets and is used for making bar soaps. KOH is a bit harder to find, and is mostly used for making liquid soaps. You normally have to buy it online from Amazon or from a soap and lotion supply type store.