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.
I’ve had this in the slow cooker for 6 hours and it is still not thickening or becoming translucent, even after increasing the heat from low to medium. I know exactly what to look for because I’ve made your coconut oil soap paste and it turned out perfectly, but it’s just not happening with this one. Is the “paste” still going to usable if it never quite gets to a thick paste consistency? It’s like thick, opaque pudding now.
Hi Rebecca, you’re on the right track. Texture during cook can vary a lot with olive oil and with KOH purity. Opaque “thick pudding” after hours usually means either the heat is a little low or your KOH is less pure than labeled. Two tips:
Do the tiny clarity test in distilled water. If that little bit dissolves crystal clear, you’re done, even if the pot still looks like pudding.
If the test stays cloudy, keep gentle heat and stir every 30 minutes. If your KOH is, say, 85–90% pure, you may be slightly short on lye. You can correct by making a small, carefully measured KOH solution and stirring in a little at a time, but most of the time more cook time plus patience solves it. The paste will still be usable once it passes the clarity test.
Hi Tracy,
I did the clarity test in a glass jar, it was creating lovely bubbles and water was clear too. But when i saw the jar the next day the bubbles at the top of water disappeared and water went cloudy. Also, when I did a PH test it comes to 10 (bright blue). Could you please explain if the soap is safe to use or not? Or anywhere i can read and learn more on this?
Many thanks,
Lorina
Hi Lorina, that behavior is common. Bubbles clearing overnight can reveal slight cloudiness from minerals in the water, temperature changes, or a tiny bit of excess oil. pH 10 is normal for liquid soap and safe for typical use. If your quick test dissolves clear in distilled water, the batch is good. For maximum clarity and shelf life, always test and dilute with distilled water, and store away from cold drafts that can haze soap.
Is there any material types like Teflon, etc, that shouldn’t be used for the pot, spatula, or storage?
Hi Sue, use stainless steel for pots and utensils, silicone or heat-safe spatulas, and glazed ceramic slow cookers. Avoid aluminum and unlined copper because lye reacts with them. For storage, glass, HDPE, PET, or PP all work well. I’m not a big fan of Teflon, but Teflon-coated tools are fine if the coating is intact.
what temp should it be cooked at/ what setting in the crock pot?
Hi Marla, “Low” on most slow cookers works well. You want steady gentle heat, not a vigorous simmer. If your unit runs hot, use “Warm.” The paste should thicken and turn more translucent over 3–4 hours with a stir every 30 minutes. If it starts to puff or dry around the edges, reduce the heat.
I just made this, and I don’t know if my crock pots low setting is to hit, but I mixed it from liquid to really thick back to creamy. I than let it set in the crock pot for 30 minutes and went back to check on it and it was one solid piece lol. What do you think I did wrong???
Hi Joshua, that can happen for two reasons, so don’t worry — your batch isn’t wasted.
One possibility is that the wrong type of lye was used. Liquid soaps need potassium hydroxide (KOH), not sodium hydroxide (NaOH). If NaOH was used by accident, it’ll thicken fast and turn solid, basically forming a bar soap in your slow cooker.
If you did use KOH, then your slow cooker probably just ran a bit hot or vented too much moisture. When that happens, the paste can dry out and harden into one solid mass. You can fix it by chopping it up and dissolving it with hot distilled water — it should soften right back into usable soap.
Next time, try using the “Low” or even “Warm” setting with the lid on to hold in moisture. That usually prevents the paste from drying out.
I am getting ready to try this recipe, but I am new to soap making. Is there any cure time required for making hot process liquid soaps like there is with bar soaps?
Hi Megan,
That’s a great question—especially if you’re new to soap making!
With hot process liquid soaps, you don’t really need to cure them at all. Once the soap has finished cooking and is fully saponified, it’s ready to dilute and use. There’s no need to wait for evaporation or hardening like with bar soaps, since those aren’t part of the liquid soap process.
That said, if you’re unsure whether saponification is fully complete, it’s fine to let it sit for a day or two just to be on the safe side. The saponification will finish on its own if it hasn’t already. Personally, I just test it, and if everything looks good, I use it right away.
If you’re interested in the deeper reasoning behind why bar soaps need curing (and why liquid soaps don’t), I go into more detail here: How, Why, and When to Cure Soap
Hope that helps—and enjoy your first batch!
Mine won’t thicken what did I do wrong
Hi Amber, a couple of quick checks help:
• Confirm you used KOH (potassium hydroxide), not NaOH.
• Make sure you weighed everything, not measured by volume.
• Give it more gentle heat and time. Olive-oil liquid soap often looks like creamy pudding rather than stiff “mashed potatoes,” and that’s OK. The real test is a spoonful dissolved in distilled water. If that bit is clear, your batch is ready even if the pot still seems soft.
Hi. Thank you for this. It sounds great. Can you store the paste to dissolve as needed – perhaps in a mason jar. How long can it be kept like this.
Hi Carol, yes, I store the paste in a mason jar with a tight lid. Keep it cool and dry and avoid filling the paste to the very top so the paste isn’t in contact with the metal lid. It lasts a year or more; I’ve kept some for several years without issues. (With time, it will start to smell a bit rancid, but can still be used for general cleaning around the house.) I dilute small amounts as needed so the main jar stays fresh.
Silly question, I’ve read over this article several times and do not see what you do when the soap is finished cooking. Are we to allow the soap to cool naturally inside the crock pot ? Should we remove the finished soap into our glass containers while hot ? Should we let the soap cool to touch and then remove it to another container? I really appreciate your help.
Hi Barb,
Not a silly question at all—it’s a great one! 😊
Once the soap paste finishes cooking, you can let it cool right in the crockpot if you’re not in a rush. I usually leave mine to cool naturally until it’s warm but not too hot to handle. Then, I transfer it into a glass or plastic container with a lid for storage until I’m ready to dilute it.
If you prefer, you can also scoop it out while it’s still warm—it’s softer and a bit easier to handle then—but just be careful since it’ll still be quite hot. Either way works fine! 💕
Please help, I recently purchased the ingredient, potassium hydroxide (KOH), and then discovered I only had (2) 16 oz. bottles of Olive Oil Pomace in my inventory. I use this oil to make CP soaps due to the cheaper price. I found a used, very clean crock pot at my local thrift store and was excited to make the liquid soap this weekend.
Will the Pomace Olive oil work in the recipe for the DIY Liquid Castile soap or should I purchase the regular Olive Oil from my supplier?
Hi Barb,
That’s so exciting—you’re all ready to make your first batch! 😊
I’m not completely sure how olive pomace oil would turn out in this particular recipe. It does have a different saponification value from regular olive oil, and I’ve always seen them listed separately in soap calculators. It’s probably fine, but since this is your first time making liquid soap, I’d personally stick with regular olive oil for now—just to keep things predictable. Once you’re comfortable with the process, you can experiment with pomace in a later batch. 💕