Liquid Castile Tutorial

The making of liquid soap has become unduly complicated by books and articles written about it. It also often includes all kinds of additives that I don’t want in my soap. I want the most simple soap with the fewest ingredients.  I gave up on liquid soap a couple of times (at least) before I decided to forget all the articles and make it in a simple natural way that made sense.  I’m a big fan of castile soap.  You probably already know that it’s mild and has a very conditioning feeling on your skin. What you may not realize is that it is also good for cleaning.  It will make glasses sparkle, shine your stainless steel appliances and do most of the household cleaning.

This soap is very simple to make.  First you’ll create a soap paste (much like making HP soap). Then you’ll dilute the paste to the viscosity you want. Castile does not need a thickener. You can make it as thick as you want by not overdiluting it.

There are three ingredients in this soap: olive oil, potassium hydroxide and distilled water. I don’t think it matters much if you’ve made soap before or not or what process you’ve used. Just follow the directions very closely. It’s a lot easier than the number of pictures would make you think.

I have created a one page printable summary of this tutorial. I suggest you print that out now and add notes to it as you read the details in this tutorial. There are a lot of good details here that are not in the summary.

If you are not a seasoned soap maker at least know how to deal with lye carefully.  Your eyes MUST be covered and you should probably wear gloves.  Your safety is your responsibility so go find out about it if you don’t know. Do not have kids or pets running around.  Most of the time you will have no problem but the time when you do, when you spill some lye, you don’t want it on your kids or dogs.

Potassium hydroxide (KOH) is the lye we use for liquid soap. It seems much more potent than sodium hydroxide (NOAH) the lye we use for bar soaps. Be sure to face away from it when you pour it. I do it on my stove under the hood fan.  Sometimes it sizzles and makes scary noises. I’m using a plastic “bucket” that I didn’t entirely trust in this tutorial so I set it in a stainless bowl, just in case.

I suggest you read through the whole tutorial before going back to the beginning and getting to work. I’ll also add a printable summary at the end. Here is the finished soap we are making:

001finished sequestered soap

A drink dispenser is the perfect dispenser for soap. If there are any un-saponifiables they will sink below the spigot. If there is any oil it will float.  In this soap you probably won’t have a noticeable amount of either so don’t worry if you don’t have one.

This recipe is going to make over a gallon. I suggest that you do not reduce the amount.  You are only using 32 ounces of olive oil and you want to have enough liquid to keep your stick blender from splashing it all over.

To begin, as always, we use a soap calculator.  This calculator is the one at I started using this one because it had the option of choosing potassium hydroxide for liquid soap. They have a simple and an advanced calculator. It allows for many variations of liquid soap that we are not using.  All we need is the oil to lye ratio and the suggested amount of water to start with.  Choose 0 for superfat. You do not need the superfat in castile and extra fat will keep you from getting clear soap or give you an oil slick on the top of your soap.


After entering the basic info: Superfat (0), type of lye ( Potassium Hydroxide) and oil type (olive) your resulting page will look like this:


Pretty simple so far, huh?

Add your lye to your cold water under the range hood or in some other well ventilated place. Be careful not to breathe in the fumes as you pour it.  Stir gently to dissolve.


This is the oil I’m using. Costco pure oil. Pure is the grade of olive oil. You do not need virgin or extra virgin oil. You can use pomace oil if you prefer. 

Weigh out your 32 ounces of oil. Since we are only using olive there is no melting necessary.


Set your crock pot to low. After pouring the oil into the crock pot, gently pour in your lye water and blend.

Important Note: This soap took about 45 minutes to get from mixed in the crock pot to a thick enough trace that the stick blender had trouble managing it.  It could take more or less time. This soap actually progressed beautifully from beginning to end.  Don’t worry about how long it takes. I use the stick blender for 1 or 2 minutes and then set my timer for 5 minutes. After those 5 minutes I come back and stick blend for another minute or two and set the timer again for 5 minutes. I do this for as long as it takes. Wearing out the stick blender won’t make it any faster nor will hovering over the pot. Relax. This soap is going to be great. Do some laundry or clean your kitchen.  Or have a cup of coffee.

046-144a 045-145

Liquid soap continues to attempt to separate longer than bar soap does. With bar soap usually once it is emulsified it stays emulsified. Not so with liquid soap. You want to make sure that you blend it back together often before it gets to thick too do so.  See in this picture how it is slightly separating?

But it comes back together quite easily, as you can see here: 043-145c 042-214 041-214b 040-226

Again it tries to separate a little…


And it comes back together again:038-226d 037-317

and again…



and again…035-317b 034-355

Now you can see it starting to get nice and thick, even though there is still a little separation.033-355b 032-355c


When it gets to be a drag on the stick blender, switch to the wire whisk.
031-355d 030-355e 029-438 I am not mixing it every five minutes now, probably every 15 or so. I don’t want to let it get too thick if it is separating, I want to keep putting it back together. Also, once it begins to thicken keep it covered.  028-438b 027-438c 026-446

Look at the color and density change. It goes very yellow and shiny.

Different oils may look different colors but the shiny “vaseline” quality is what shows you clearly that it is done. Look at the picture below. This is beautiful soap. It is a very nice consistency. Often it is thicker and stiffer than this which is harder to mix and harder to dilute. This is perfect. We might be able to cook it faster on a higher heat but this soap has been perfect at each step so I’d rather take my time with it.


Lye Excess (Zap) and Clarity Testing

We want to test our soap paste for two things: excess lye and clarity.  The lye gets a standard zap test.  The soap making part of this process is done when the paste is done. After the paste is done you are going to work with it and manipulate it, but it is not dangerous and the chemical process is finished for all intents and purposes.  It is not finished until it passes the zap test.  If you’ve never done this, it’s a matter of touching the tip of your tongue lightly to the soap and gauging the feel of it. Don’t do it with hot soap, obviously. Let some cool a little on a spoon (you could do your clarity test in the mean time). If your tongue feels like you touched it to an alka seltzer tablet or a fizzie or a 9 volt battery, it’s still got active lye and is not done.  That’s the zap test.

Testing for clarity:   Mixing a little soap paste in with water will show us if the soap is going to be clear.


Glob dropped into water…022-446e

Now look at the picture below: you can see that even though the soap hasn’t entirely dissolved it has enough to turn the water a yellowish color and that yellowish color is quite clear so our soap passes the clarity test. Note that there is nothing wrong with soap not being clear. It can be cloudy – it’s just a matter of preference. Castile will always be clear but some additives could change that.  It shouldn’t be milky looking. That would mean it wasn’t done. 



With the soap paste finished we are ready to dilute it.  Your crock pot will not be big enough to do this. Let’s consider a couple of things. Even if you are someone who never uses your food cookware for soapmaking, you are safe in using it for this because you are not making soap, the soap is already made. There won’t be any lye reactions. You could even use aluminum. (although I try to keep aluminum out of my house entirely).  If you have to buy a pot, Walmart has some cheap stainless pots that are great for soapmaking You can get an 8 quart pot for about 11 dollars but I’d go with a 12 qt. for slightly more.   If you are absolutely stuck using a smaller pot you can get it mostly diluted and then transfer it to a bucket or other container to finish it but it must be diluted to a pretty syrupy consistency, much like this soap looks at the end.

There are no fancy tricks to soap dilution. (Well, I do have one sort-of-trick, I’ll get to that in a little while.) There is only patience and not overdoing it.  Soap pastes made from different oils will dilute with very different ratios of paste to water. Coconut will use the least water with about a 1:2 ratio of paste to water. Castile will be one of the highest with a ratio of about 1:4 or 1:5. For this batch I used 32 ounces of olive oil and ended up with about 160 ounces of nice thick finished liquid soap.  Keep in mind that soaps will vary greatly depending even on the brand of oil used.

In the picture below I’ve added about 100 ounces of boiling water to my soap paste.  We are going to add only hot water and you need to keep track of how many ounces you have added. (My pot is probably much bigger than you will be using which I mention just so you understand the scale in these pictures) Once you’ve made this a couple of times you will add most of your water at the beginning because you’ll know how much you can safely add.


Simmer the soap. If you have infinite patience – or your soap paste is finished in the evening –  you can just leave it overnight and let it begin to dissolve on it’s own. If you are like most of us you will have to poke at it and break it up, which will actually make it dissolve somewhat faster as more surface area will be exposed to the hot water.

Do NOT let your soap boil. Soap will boil out of a pot and cause a huge bubbly mess in a very short time. Keep the flame low and if necessary put a heat diffuser under the pot.  (Boiling won’t hurt the soap, fortunately, but it will make an ungodly mess. On the upside, everything it boils onto will be sparkly clean.)

The soap does not have to simmer the entire dilution time.  As I said before, you could just leave the hot water overnight and let it work. Sometimes I’ll heat it up a couple of times because heating it speeds up the process some.  And of course, if I’m going to be away from the house I’ll turn it off and back on when I return. While heating and cooling you are evaporating some of the water which is another reason it’s hard to figure an exact amount you’ll need for your soap.

These dilution photos span about 3 or 4 hours.



What it is mostly diluted mashing it with a potato masher will help dissolve some of the pieces left.


After soap cools it always looks like this picture: It will have a foamy crust on the top. The crust may consist of just the foam or it may have soap 1/4 inch or more under the foam that is not dissolved.  This shows you that the soap solution is as saturated as it will get. More water must be added in order to dilute the balance of the soap. Do add more water if the soap is very thick and so is the crust but first let me show you a trick of sorts. Or a safeguard against over dilution.


Look at the picture below. I have folded back the crust over itself like an omlette.

Here is an enlargement of part of the picture above:


As you can see there is still a good bit of undissolved soap in those translucent chunks but you can also see that the soap below the crust is beautiful and perfect (and should be quite thick).  You want your soap “finished” at this phase when it is a little thicker than your final thickness. Most instructions that I’ve seen have you adding bits of water and heating and adding a little more until your soap is perfectly dissolved but …

aint nobody got time

So here’s what you do instead, Gently lift that “crust omelette” out of your pot and put it into a bowl or another pot. Pour off your soap into a beverage decanter or whatever vessel you will be using and then put the “crust omlette” back into the dilution pot add a bit of water (use about an equal amount of water as you have crust) and do the dilution thing again, on a smaller scale.  You still don’t want to over dilute it but now that most of your soap is safely out of the way of ruination, you don’t have to be quite as careful (and at times, when very little soap was left undiluted, I just tossed it in the trash. You have to balance the cost of your time with the money that soap will earn)

In any event it seems that there is always some slight crust on top unless you have overdiluted the soap and that is way more time consuming to fix.  Also note that even if the soap is almost perfectly diluted, those bubbles (that alcohol never seems to remove) will turn into a slight crust hiding over-diluted soap under them, so watch for that and skim all the bubbles  you can off the top while the soap is simmering.

004-530 003-531

You can see how thick this soap is by the picture of the tipped pot. It is very thick but it is liquid enough that I can mix hot water into it and stir, to the perfect consistency.   

Some liquid soaps do need to “sequester” for a while. Castile is not notably one of them. I could bottle this the day it’s made and it would be fine. However, depending on your oils and any superfat (by design or accident) it’s a good idea to let it set for a few days and settle.  I usually fill the bottoms of my decanters with sterile rocks or marbles up to the point of the spigot hole. This wastes less soap at the bottom. Also, don’t turn the spigot on until you are ready to bottle your soaps or it will likely clog.

001finished sequestered soap

Bottling your soaps from this decanter is very easy as long as the spigot has not clogged. If it does, use a tiny dental brush to unclog it. (These little brushes come in handy for lots of other things too).


Click here for a summary of this tutorial that you can print.


A couple of answers to questions I know I’ll get. 

To add scent or color to finished soap, do so as it is cooling. Scent should be added while soap is still hot. Some scents might thicken or change your soap. I would try a small sample, not a whole batch.

I do not know how this soap will act if you use glycerin instead of part of the water. I do not consider liquid soap made with glycerin as “natural handmade soap” so I won’t be trying it.  I also don’t know how it will work with milk or any additives. Please do let me know about your variations and how they do.

Have fun!!!!  Blessings on all you soap makers and all those you touch!

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