Classic Bells > Soapy stuff > Liquid soap: Tips for making it

Liquid soap: Tips for making it

Potassium hydroxide is required

First things first. Potassium hydroxide (KOH) is the alkali needed to make liquid soap. Sometimes a bit of sodium hydroxide (NaOH) is included in liquid soap recipes, but KOH must be the main alkali if you want to make soap that can be diluted into a a stable, pourable liquid soap.

The corollary is sodium hydroxide (NaOH) is the alkali needed to make solid soap. Sometimes a bit of potassium hydroxide (KOH) is included in bar soap recipes, but NaOH must be the main alkali if you want to make acceptable bar soap.

Some people make "liquid soap" by adding water to shredded bar (NaOH) soap to create a pourable mixture. Other experienced liquid soap makers and I have tested this idea multiple times. We have found a mix of sodium soap and water might be a decent liquid soap for a few days to a week or two, but the viscosity (thickness) does not remain stable and the texture can become unpleasant. There is nothing wrong with trying this idea out, but do not be surprised if your results are not impressive in the long run.


Getting started

If you are completely new to soap making, I do not recommend starting with liquid soap. Start with solid bar soap made with sodium hydroxide and then come back to liquid soap making after your general soap making skills are honed.

If you already make bar soap and want to expand into making liquid soap, I recommend reading this article first --

Liquid Soapmaking -- Where to start by Jennifer of Miles Away Farm


Making your first batch of KOH soap paste

Build your skills by making a basic liquid soap paste following a tutorial from a reputable source. I recommend using a cold process method and making sure the recipe has a low (1-3%) superfat. Avoid recipes that require neutralization with citric acid, borax, or boric acid.

You can make soap for bathing and handwashing or you can make soap for household cleaning. Here are several tutorials that I recommend --

Cold Process Liquid Soap by Susie. She gives her general method and several recipes for bath and household soap. Pick a recipe and follow her general method.

Clear Glycerin Liquid Soap by Irish Lass -- see posts 8 and 9. You can follow Susie's general method and use Irish Lass's recipe.

Safety caution! For safety's sake, KOH should be dissolved in room-temperature water, not in hot glycerin. Please follow her directions for dissolving KOH in water. Ignore her directions for dissolving KOH in glycerin.

Cold Process Liquid Soap Making by Christine of Alpha Omega Soaps.


Tips for success

Keep your first batches simple! Limit ingredients to the basics -- water, KOH, fat, and possibly glycerin.

Keep each batch size small A total of 100 to 300 grams of fat will make a LOT of liquid soap after it is diluted.

Do not get hung up on all changes in texture and appearance that you are "supposed" to see. Some authors provide detailed descriptions and photos of the various texture and visual changes their soap goes through as it saponifies. These changes may or may not happen to your soap. If you do not see every stage shown in the tutorial, do not fret. Just keep moving forward with the process, and your soap will very likely turn out just fine.

There is no need to cook liquid soap for hours and hours, even though I realize many recipes are written that way. Most liquid soap is fully saponified within about two hours, and often the soap is done within one hour.

Be gentle with yourself. Liquid soap making can be frustrating, especially at first. Once you get used to it, you will learn that liquid soap making is a forgiving process. If you need to take a break, simply remove the soap pot from heat (if using heat), cover the pot with a tight fitting cover, store it in a safe place away from pets and people, and let the soap sit for a few hours or even a day or two. You may return to find the soap has finished saponifying all by itself without your help.

Neutralizing liquid soap with borax, boric acid, stearic acid, or citric acid is not necessary if you use a recipe designed with a small amount of extra fat (positive superfat). (See the tutorials listed above for no-neutralization recipes.) Some liquid soap recipes, especially older ones, are designed with a small lye excess (negative superfat), and these do require neutralization. I strongly recommend you avoid these neutralization-required recipes until you are comfortable with the liquid soap making process and want to explore this alternative method.

Work your way up to more challenging projects. After making a batch or two of basic liquid soap, create your own liquid soap recipe or try more complicated recipes such as the Creamy Cocoa-Shea Glycerin Liquid Soap by Irish Lass


What to do with KOH soap paste

Use as-is. Soap paste (the thick saponified soap before it is diluted) can be used directly for general household cleaning. A 100% coconut oil soap paste is a good choice for this purpose. Put a dab of paste on a sponge or cloth for washing dishes or scrubbing the shower.

Some people pack soap paste into lip-balm-type tubes for washing hands in public restrooms. The tube of soap stores easily in a purse or pocket until a dab of soap is needed. A good recipe for this purpose would be a mild bathing-soap recipe.

Dilute to a pourable thickness. Another use for soap paste is to dilute it to a pourable consistency. Many soapers use one of three approaches for diluting their soap --

Dilute to a honey-thick consistency (high pure-soap content) for use in a squirt or pump bottle
Dilute to a watery consistency (low pure-soap content) for use in a foamer dispenser
Dilute to a moderate to high pure-soap content and thicken if desired with a separate thickener

There are two general types of separate thickeners that can be used with liquid soap --

Table salt or other salts
Cellulose- or gum-based thickeners

Dilute only what you need. Keep in mind you can dilute only a portion of the paste to meet your current needs and store the rest for later dilution. Store unused paste in a tightly closed jar or plastic bag in a dark, reasonably cool storage place. Some people even store it in the refrigerator.


Basic rules for diluting

Use the right soap recipe. If you want your soap to be honey-thick just from dilution alone or if you want to use salt for thickening, the soap should contain about 50% oleic acid.

If the oleic acid content is a lot lower than 50%, the soap will never be thick by dilution only or by using salt. A separate non-salt thickener must be added.

A 100% coconut oil liquid soap is an example. There is not enough oleic acid in this type of soap to create a thicker consistency by dilution only. To thicken a low-oleic soap, dilute to the desired soap concentration and add a separate cellulose-or gum-based thickener (see below).

A thin soap is not always a problem, however. If you want to use your soap in a foamer dispenser, for example, the soap has to be diluted to a watery consistency. In this case, a recipe with a low oleic acid content will work fine.

If the oleic acid content is a lot higher than 50%, the soap might be pourable for a short while after dilution, but it may revert back to a non-pourable jelly, even after adding a lot of water.

A 100% olive oil (castile type) liquid soap can behave like this. Avoid this problem by reformulating the recipe to lower the oleic acid to about 50%.

Use only water for dilution. Never dilute liquid soap with honey, aloe, milk, beer, or other liquids that contain sugars, starches, or proteins.

These sources of food greatly increase the risk of microbial growth in the soap. Remember -- microbes do not have to be visible to the human eye to cause infections or disease, as anyone who has had food poisoning will know. Play it safe with your soap!

Use only water to dilute liquid soap, preferably distilled water or reverse osmosis water. I recommend distilled or reverse osmosis water for best results. Filtered rainwater can be used in a pinch. If you only have drinking water for dilution, it can be used, but be aware that minerals dissolved in drinking water may make the soap cloudy and reduce the lather.

Heat is helpful but not required. I dilute my soap paste using warm water but I otherwise do not heat the soap. This is a hands-off method that is energy efficient. The tradeoff is the soap will need several hours to a day to fully dilute.

Other people want faster results so they use a hot water bath (bain marie), oven, or a crock pot. The added warmth speeds dilution, but you do need to pay more attention to the process.

Check the thickness of the soap at room temperature. Always evaluate the diluted soap at normal room temperature before deciding whether to dilute further. It is normal for liquid soap to be thinner and often more transparent when warm. It will become thicker and sometimes less clear when it cools.


"Dilute to honey thick" method

Do not add all the dilution water at once. Many liquid soap making tutorials use the "dilute to honey thick" method. They often give the impression you can measure X amount of water in proportion to the paste, mix the whole amount of water with the paste, and end up with a perfect honey-thick soap every time. If your recipe varies from the tutorial, your soap may not dilute the same way as the author's soap.

You will get better results if you remember "slower is faster" when diluting, especially when making a recipe new to you. Keep good notes about how much water you use, so the dilution process will go faster the next time you use the recipe.

Add about 1 part warm water by weight to 2 parts soap paste. Mix the water and paste together as best you can. A potato masher works well to break up large lumps in the beginning. Later on, a whisk, spatula, or even a stick blender will be helpful.

When this first portion of water is fully mixed into the paste, check the thickness and consistency. If more water is needed, add 1/2 part warm water to the mixture. Mix and check. If more water is needed, add 1/4 part water. Check. Continue diluting with decreasing amounts of water until the soap is close to the desired thickness. Near the end of dilution, you may be adding 1 teaspoon of water at a time.

Sometimes lumps of firm paste or a floating layer of firm soap refuse to dilute nicely. If that happens, you can remove those stubborn bits and dilute them in a separate container. This reduces the chance you will over-dilute the main portion of soap.

Susie explains how she uses this method of dilution in her tutorial. Look in Post #1 for the line "To dilute" in this tutorial.

For a tried-and-true recipe, you can speed the dilution process a bit --

Add about 3/4ths of the total dilution water you used the last time.

Check the thickness, add a bit more water if needed, check again, and so on.


Pros and cons of the "dilute to honey thick" method

When I dilute liquid soap as described above until the soap has a honey-thick consistency, the amount of pure soap in the finished product ranges from 30% to 40%. For general-purpose handwashing and bathing, this percentage of pure soap is higher than necessary.

A concentrated liquid soap is more wasteful. When people wash with bar soap, they usually rub the bar enough to get the right amount of soap for the job. When people use a liquid soap product, they tend to squirt the same number of dollops onto their hand or washcloth. Even if half a dollop is enough, many people will still use a full squirt or more.

In addition, the concentrated soap can over-clean the skin and strip away desirable skin fats. The result is the skin can feel dry and tight, even irritated. This will be especially true if the liquid soap recipe includes a high percentage of coconut oil (in other words, more lauric and myristic acid).

There are also limits to how thick a soap can be if using a dilution-only method. It is near impossible to produce a stable, thick gel, for example. Separate thickeners may be required to achieve this texture.


"Dilute to a specific pure soap content" method

The "dilute to honey thick" method is simple, but it is not always the most ideal method. As an alternative, consider diluting the product until the pure soap content is 8% to 20%. (1) The advantages of this include --

Reducing product waste while still cleansing well
Reducing the chance of drying or irritating the skin
Building lather more easily
Controlling costs if you sell

This extra dilution will reduce the viscosity. If using foamer dispensers, the soap will probably need to be diluted more -- perhaps to about 10% pure soap content -- to dispense properly.

If you want a thicker product, I suggest diluting to a 15-20% pure soap content and then use a separate thickener to increase the viscosity to the desired thickness.


Calculate the pure soap content

I created a simple calculator to help you figure out how much water is needed to dilute soap paste to get a liquid soap with a specific concentration of pure soap.

Click here to use the calculator....

The calculator will open in a new browser window. The formulas are explained in "Extra credit" section at the bottom of this article.


Thicken with table salt or other salts.

Soap that is moderate to high in oleic acid can be thickened with a careful dose of table salt (sodium chloride). A soap that is low in oleic acid, such as a 100% coconut oil soap, cannot be thickened with salt.

Other salts, such as potassium carbonate or sodium carbonate, can also be used to thicken liquid soap. There are two downsides. One is that salts tend to reduce lather.

Another is that salt will provide maxiumum thickening only in a narrow range of concentration. If you add too much salt, the soap will thin out again, and this problem is impractical to fix.

If you have not thickened soap with salt before or if you are working with a recipe new to you, I recommend you experiment with a small sample of soap first, find the amount of salt that works best, and use that information to thicken the main portion of the soap. To thicken with salt --

Dissolve 1 part table salt in about 3 parts warm water to make a brine. The total amount of brine will depend on the amount of liquid soap you want to thicken. For a small amount of liquid soap, you might dissolve 1 teaspoon of salt in 3 teaspoons of water. Set this brine aside.

Dilute the soap to the desired viscosity or to the desired percentage of pure soap. Stir a small amount of brine into the diluted soap. Salt takes awhile to do its magic, so let the mixture sit for about 30 minutes. Check the thickness and stir in another small portion of brine if needed. Stop adding brine when the mixture is sufficiently thick.


Control thickness with cellulose- or gum-based thickeners.

You can use a separate cellulose-based thickener such as HEC (hydroxyethyl cellulose) or HPMC (hydroxypropyl methylcellulose) to thicken liquid soap to your desired viscosity. Some makers have tried thickening liquid soap with guar gum or xanthan gum with varying amounts of success. These thickeners can be especially useful if --

You want a thicker gel than you get from dilution alone or by using salt
The soap has a very low or very high oleic acid content

I do not have experience with these thickeners, but Faith Oriold has several good tutorials to guide you. (2)


Adding fragrance

Add fragrance after the soap is fully diluted. Most people report they scent liquid soap more lightly than bar soap, so start with 0.5% to 1% by weight of diluted soap and see what you think.

Test the fragrance in a sample of diluted soap to learn if the fragrance alters the texture or appearance of the soap. Some fragrances thicken liquid soap, others thin it out, a few cause the texture to become clumpy or grainy, and some scents do absolutely nothing. There is no way to know what will happen except to test a sample.


In conclusion

I explain more about liquid soap making and recipe design in the companion article "Tips for desiging good recipes." Even if you are not ready to design your own recipes, you might want to skim this second article for more tips about liquid soap making.



1. Jane Barber. Active surfactant calculator. Making Skincare.

2. Faith Oriold. Tutorials -- Liquid Soap. Alaiyna B. Bath and Body.



Extra credit. The formulas used in the Pure Soap Content calculator are described here. These formulas can be used with grams or weight ounces. Use only one unit of weight for everything -- do not mix ounces and grams.

1. Determine the pure soap weight, paste weight, and percentage of pure soap for the entire batch.

Total pure soap weight = Fat weight in the batch + KOH weight in the batch
(Get these weights from your recipe)

Total paste weight = Weight of the entire batch of soap paste
(Weigh the whole batch of finished paste after it is made)

Pure soap % in the paste = Total pure soap weight / Total paste weight X 100

2. Choose the percentage of pure soap you want in the diluted soap. I am calling this the "Dilution%" in the formulas below. This percentage must be equal to or less than the "Pure soap % in the paste" that you just calculated.

3. Measure out the weight of soap paste you want to dilute. I am calling this the "Paste weight" in the formulas below. You can dilute the whole batch of paste or only part of the batch -- that is up to you.

4. Calculate the weight of pure soap in this amount of soap paste --

Pure soap weight = Paste weight X Total pure soap weight / Total paste weight

5. Calculate the water needed to dilute the paste to the Dulution% you chose --

Dilution water weight = Pure soap weight X 100 / Dilution% - Paste weight

6. Calculate the total weight of the diluted soap --

Total diluted weight = Paste weight + Dilution water weight