Who doesn’t love liquid soap? Although a soap bar has its own charm and is very handy since it doesn’t need a container, liquid soap is easier and faster to foam. Then it’s a matter of preference, some people prefer soap bars, some people prefer and can’t live without bath gel and liquid hand soap.
By learning how to make liquid soap, you are actually opening the door to a lot of DIY: hand soap, bath gel, dish washing soap, laundry soap,… The method is the same, only the ingredients will change.
Previously in this Soap Making series: How Do You Make Natural Soap At Home?
How To Make Liquid Soap With Potassium Hydroxide?
The internet is filled with posts about How To Make Liquid Soap With A Soap Bar, where its stated is homemade liquid soap, but this is nothing but transforming a soap from solid to liquid form. Some recipes are even a bit irresponsible as they propose to use a commercial soap bar (usually not soap at all) and heat it, which might chemically change and alter some substances, even producing toxins in an extreme case.
This liquid soap, made with natural ingredients such as vegetable oils and potassium hydroxide, is not only pure and of high quality, is also very economical, as a small amount of soap paste (500g) gives you easily 1,5 to 2 liters of soap. This soap is made by using a crock pot and a hot process method, but it’s not as complaicated as it sounds. I will guide you through the steps along this tutorial.
As this soap can only withstand 3% of superfat (or it separates), glycerin can be added for additional moisture and glide. I personally think that the soap made with distilled water only, as a hand soap, is good enough, so the addition of glycerin is optional. You can also add scent, but, again, it’s optional.
I’ve learned how to make liquid soap with all-natural ingredients from the website Lovely Greens. The author explains everything in detail, but in simple terms, and when necessary providing a reason to do something this way and not that way. The part where you make the liquid soap does require some trial and error though, and it’s not straightforward.
This tutorial adds up my experience and simplifies the process even further. You will find a detailed step-by-step tutorial that will show you how to make liquid soap with potassium hydroxide (also known as potash). Every recipe in this blog will also have its own recipe video, but this is a complete and detailed tutorial, where you can learn all details, special tips and hopefully clear all your doubts.
Let’s not waste another second and jump to the tutorial.
Watch These Tutorial Videos
Transforming the ingredients into natural liquid soap
What is the main difference between soap bars and liquid soap? Its the alkali substance you use. In other words, you make soap bars with sodium hydroxide (lye) and you make liquid soap, more correctly, a soap paste, with potassium hydroxide (potash).
And what is the main difference between cold process and making this liquid soap? Heating. Making liquid soap from the scratch is very close to hot process soapmaking. So, you will need a slow cooker or crock pot.
I have read a lot about hot process soap and got confused with all the details and steps. It really sounded complicated. But after making liquid soap and Rebatching Cold Process Soap (another method involving heat), I feel ready to try hot process. Some soap makers swear that after making hot process soap you won’t want to use any other process!
Anyway, a slow cooker is mandatory for this process, you won’t be able to check out temperature while making this liquid soap. An electrical stove and a double boiler system will also work out. But you need a system that auto-controls temperature, otherwise it will be really complicated.
Apart from that, the process requires patience but it’s relatively easy once you are able to recognize the various steps.
Similar to cold process, or any soapmaking process, it involves many ingredients and steps, and some accuracy, so it is very important to keep everything organized.
These step-by-step instructions for making handmade soap presented in this session are generic and, apart from some details, serve to follow any type of liquid soap recipe.
Step 1: Gather the ingredients and equipment
It is important to have everything prepared and organized before you start preparing the soap batter. This includes measuring ingredients, preparing your workstations and organizing equipment. Because the time factor is critical, it is not advisable in the middle of the recipe to pick up any missing ingredients or necessary equipment.
It is also not good practice to measure ingredients in a hurry, it leads to measurement errors and can compromise the quality of the final soap, for example, adding too much lye can make the soap irritating to the skin – pure lye burns your skin!
Take the time to read and understand all the steps in this tutorial, as well as each recipe. Then, prepare everything you will need for the recipe. Never failing this important preparation step is halfway to a smooth and sucessful soap making experience.
Step 2: Measure all ingredients and prepare your workstation
The quantity of oils and lye is critical to a good soap. It’s very important to follow the right quantities with an error close to 1 gram.
IMPORTANT NOTE: If you happen to make small mistakes, better have a little more oils and a little less lye. For example, if you are measuring 64g of lye, better to have 63g than 65g; if you are pouring some oil and you need 400g, better to have 402g than to have 398g. The calculated superfat should be able to “cover” these errors anyway. But never make or formulate soap in cups, spoons or worse, eyeballing ingredients. Always use weight.
Still, liquid soap is made in two main steps: making the soap paste, and making the liquid soap. Let’s cover preparations for the two stages.
Weigh the quantities of oils and butters with a scale. Being an important step, it requires some attention:
– Place a bowl or, if possible, the slow cooker container where the oils will be heated on the scale and set the scale to zero (usually the “tare” button). Then the oils are weighed one by one, taking care to “reset” the balance for each oil.
– Weigh the water and potash using a scale. Place each ingredient in a separate container: a heat-resistant jug for water, a cup or bowl for the potash.
After measuring ingredients, organize everything in workstations or work areas that must include the following utensils:
- an area to prepare the soap batter, where you should have at the ready the slow cooker, 2 spoons, 2 spatulas (you can then define what works best for you – I only use spatulas), a strainer, a plate where to put dirty items, some squares of kitchen paper and the immersion blender already plugged and prepared.
- an area to mix the water with lye. It is important that this area is well ventilated, ideally outdoors, or under a window. This area should have: a stainless steel spoon or silicone spatula, a large container with cold water to cool the lye water (potash water?) or potassium hydroxide solution.
In this stage, you will need to weigh liquids for the final liquid soap, like essential/fragrance oils, water and vegetable glycerin. Essential oils or fragrance oils should NOT exceed 3% of the liquid soap amount. Apart from that, measuring ingredients at this stage is not so critical, and you can even add a “little bit” of water or glycerin.
IMPORTANT NOTE: you can use pretty much any liquid, just like in cold process, however, sugary substances like milk, herbal infusions or honey will contribute for a bacterial-friendly environment, something you want to avoid. Why? Because liquid soap uses water in its final product, unlike soap bars, that cure to lose all water content.
The amount of liquids at this stage depends a lot on how you wish to produce your final liquid soap (if all at once, or in batches along time).
– Weigh the water and glycerin using a scale. You can place each ingredient in one container (one jug).
– Weigh your dye, although is something you might not find in my recipes. I love the natural color of liquid soap: yellow to golden yellow.
– Weigh the essential oils or fragrance oils and your preservative (if you decide to use it) into a small bottle
Organize your working areas for this stage that must include the following:
- an area to make your liquid soap. You will need the slow cooker again, a couple of spoons/spatulas and a dish for dirty items. A jug with extra water might be necessary. At the end, you will also need the small bottle with essential oils and preservative, depending on how you wish to make your liquid soap
- an area to pour your liquid soap into containers. You will need to have available your jars or dispenser bottles (wherever you decide to store your liquid soap), a bowl, a strainer, a spatula and the slow cooker container with the liquid soap.
I advise to continue reading and come back to this section later on, after reading the tutorial up to the end, as this greatly depends on how you wish to make your liquid soap. If you still have doubts, leave a comment below.
Step 3: Starting the soap paste – melt / heat the oils
Is everything ready? So let’s start making soap!
There are recipes that start by melting the “solid” oils (coconut oil, palm oil) over very low heat, and adding the liquid oils as soon as the first ones have melted. I put everything together and heat the oils until small pieces of the solid oils are left and let the rest melt out, mixing.
No need to use the microwave in this case, you can and should use your slow cooker – in LOW heat.
When small bits of solid oils are floating, just mix until they vanish.
Step 4: Prepare the lye water (potassium hydroxide solution)
Using potash can (and should) be intimidating, however it is a necessary ingredient in soap making. All soaps, even glycerin bases, are made with either sodium hydroxide (lye) or potassium hydroxide – they are a basic ingredient.
While the oils are heating up in the slow cooker (don’t let them heat up too long unattended), let’s prepare the lye water.
First, put on your safety equipment: gloves, glasses and mask if there is not enough ventilation. You must have clothes that cover your legs and arms, and shoes that cover your feet. Make sure that there are no children or animals in this area, to minimize the risk of accidents.
Now, be prepared to place the container where you will make the solution (ideally in pyrex or stainless steel) in a container with cold water or on an outdoor surface (a bench, for example). As soon as you mix the potash with water, it will reach temperatures in the order of 100ºC – 210ºF!
Do not use the refrigerator or an enclosed area to cool the mixture, because of the resulting vapors that are corrosive and toxic.
Safety first: use ALWAYS gloves and glasses at all stages of soap making, especially when dealing with potash or the lye water.
Mix water and potash
Water (at room temperature) and potash should be already measured in separate containers. The container with water, where you are going to make the mixture, must be made of pyrex, glass or polypropylene (PP) plastic, that is, resistant to high temperatures and chemical corrosion.
Slowly pour the potash into the container with the water and mix well with the stainless steel spatula or spoon. The solution will heat up and release harmful vapors, especially at this time. Be careful and avoid breathing vapors. Mix very well so that the potash completely dissolves in the water.
If you have made cold process soap and are used to making lye water, be prepared for the extra-firework – potassium hydroxide reacts stronger than lye with water, and you will probably hear a lot of efervescent noises. Just make sure that your equipment and counter is prepared for high temperatures, and keep your safety equipment on all the time
Note that pouring water over potash can have a really violent “volcano” effect, where you might get burned with water spilling! Always pour the potash over the water.
It is also important to ensure that the water is at room temperature (25º), especially if you are using an herbal infusion. Even if it is only lukewarm, the “volcano” effect can be dangerous.
In the meantime, I’ve felt the need to write a post focused on preparing the lye water alone: How to Make Lye Water. See the simplest way of making lye water, although you can add colorants or addictives to it, depending on the recipe.
Lye water made with potash (should we just call it potash water? :D) is basically the same, apart from a sightly stronger reaction with water.
Step 5: Mix the lye water and oils
Keep your oils inside your slow cooker, and the heat set to LOW. Using a strainer, strain your lye water into the oils carefully and avoiding spillage of any sorts – you do have your gloves and glasses on, right?
Be careful will spillage: my slow cooker is aluminium in its outer structure and it has a nasty stain from lye water spilage and dissolving the aluminium afterwards… It was not more that a few drops.
Is lye water and oils temperature important like in cold process?
Nope, not really. I always let the lye water to cool down a bit, and I never allow the oils to heat over 60ºC (they change with high temperature), but from what I’ve read is not critical like in cold process.
Even if your lye water goes down to room temperature, I think you can still make the soap with no issues, the process with the stick blender might just take longer.
You can use milk, herbal infusions, honey or sugars, just like in other soapmaking methods. However, liquid soap contains water in its final product. Water and sugars (even herbal infusions are a sugary environment even if not sweet) make for a good and friendly bacterial environment, and the usage of a preservative is mandatory. Before you have some experience, I would stick to plain distilled water – the soap is great even if simple.
Step 6: Stick blending your soap
Now the interesting part will begin! Be ready for different stuff, even if you are experienced with cold process. There’s not really a “trace” phase here, as the soap will turn from liquid to solid almost instantly.
Set your slow cooker to HIGH heat, and insert the immersion blender into the mixture and tilt it to release air bubbles. Turn on the blender for very short periods of time and then mix it up a little, using it as a spoon. The mixture will slowly stop being “oily” and start to take on a more milky and opaque consistency, especially when you switch on the blender.
Now, let’s cover the different phases:
– your soap batter with start to emulsify, turning into a whitish, mayonnaise-like substance, especially in the zone where you stick blend;
– after a while, the soap batter will almost all be emulsified, but with oils floating, looking like it wants to separate – it will not be fully homogeneous;
– Run the process of stick blending and mixing for 5 to 10 minutes, then let the soap rest and heat for 5 minutes. Keep doing this for around 30 minutes. The soap batter will thicken a little bit but apart from that will remain the same – like it’s separating. This is normal.
– At some point, the soap batter will instantly seize, whether you are stick blending or letting the soap rest and heat. The looks will be similar to solid pudding. Stick blend and mix while you can.
– When stick blending becomes very difficult, mix with a large (and strong) spoon. Your soap batter will turn into something very similar to mashed potatoes. Just mix it so it won’t burn or stick.
Note: If you do not use an immersion blender, and choose a hand whisk or spoon, I have no idea how long this will take….. Hence it is essential to use the immersion blender
Step 7: Cooking your soap paste
After you reached the “mashed potatoes” stage, set the slow cooker to LOW heat. Now, you just need some patience. The soap should remain in low heat for around 6 hours. Mix the soap paste every 30 minutes, in order to keep it from burning or sticking to the slow cooker.
After 6 hours, turn the heat off and let the soap paste cook in its residual heat (preferably overnight). This time should be enough to completely saponify the soap paste.
Along the cooking period, the soap paste will turn from mashed potatoes to a translucid substance, like yellow-amber vaseline.
Step 8: Finishing your soap paste – Testing the soap paste
Liquid soap making is trickier than cold-process soap making because we are using potash instead of caustic soda. With potash being only 90% pure, it can cause your soap to be lye-heavy, and harsh on the skin, or overly superfatted and cloudy. You can have everything measured correctly and this can still happen because of the lye’s 10% of other substances. That’s why testing your soap is very important, and unfortunately, it needs to be done for every batch of liquid soap you make.
After the soap has finished cooking, stir a teaspoon of soap paste into half a cup of scalding hot distilled water. Let it sit and dissolve, giving it another stir if it needs help breaking up. Let it cool completely then have a look.
If there’s oil on the surface, or if the liquid is milky and opaque then you still have unsaponified oils in the paste. Set the slow cooker to LOW heat and continue cooking the soap paste it until it’s much clearer.
Just to be clear, milky means you can’t see through it at all. If you have a translucent liquid then the soap paste is ok.
If your liquid soap is milky it means it has too much superfat, so anything more than 3%. It can cause all kinds of issues after adding your essential or fragrances oils, being the most common soap separating afterward. Also, too much oil can separate anyway and float to the surface, after you dilute the soap paste in water.
Testing excess of lye
Testing pH and its usefulness in soapmaking is another quite controvertial subject. To such extend that I’ve decided to make a dedicated post about it later on. So, I am not going to extend myself much further.
You can test for excess lye by two ways:
- Checking its pH
Dilute 1g soap paste into 99g of scalding hot distilled water and let it cool to room temperature. Take the pH strips (Litmus test papers) and check to see if the soap is between 9-10. Allow the paper to dry completely for the most accurate result.
Liquid soap is supposed to be alkaline, but if its pH is above 10 then your soap is lye-heavy. However, do not take this testing too seriously, as pH strips may have a wide range of variability – meaning that before throwing your soap away, adjust down pH, just in case. Find here further information on testing liquid soap.
You can also crosscheck with the test below.
- Zap testing your soap
This one is quite tricky, as you test soap with your tongue. First of all, DO NOT use your tongue directly in soap to run this test. Instead, do it as per the SoapMaking Forum sticky post.
If your soap is lye heavy – pH at 10 or it zaps in your tongue – lower its pH by adding diluted citric acid in the next stage – making the liquid soap – but don’t go below 9 or it will destabilize. Start with 1/2 teaspoon of citric acid diluted in 1 teaspoon of distilled warm water (or a bit more, just to dissolve the powder).
Your soap paste is ready!!
Your soap paste has a shelf life of 1 to 2 years, depending on the shelf life of the oils used. Consider the shelf-life of your paste to be the closest “best by” date of your oils. If you plan to store it, use a airtight, disinfected container. You can use it liquified as liquid soap (the most common) or you can use it as-is, as a paste.
Step 9: Starting your liquid soap – Measuring ingredients
You can use two methods to make your liquid soap:
- Make it all at once and add a preservative
- Make small batches of liquid soap that last 3 to 4 weeks (after this, your soap might start growing enough bacteria to be harmful)
Regardless of how you do it, making liquid soap follows the same rules, independently of the quantities you use.
Measure the soap paste, the water and glycerin according to your preferences, and pour them into the slow cooker. Measure the remaining addictives as well (fragrances and preservative), but keep them in a separate bottle or cup.
Apart from the essential oils/fragrance oils usage of a maximum of 3%, quantities in this stage are not that important. All the quantities presented below are more like guidelines to make your liquid soap.
The recipe I followed at Lovely Greens uses water and glycerin to dilute the soap paste. It also uses 100g of liquids (80g of water and 20g of glycerin) for 100g of soap paste.
Dilution rates for thick soap
I’ve actually found rather difficult to dissolve all the soap paste using these quantities, therefore, I have increased the amount of liquids from 1:1 to 1:2. I’ve also made soap with and without glycerin and the difference is not noticeable, so, as a personal choice, I’ve decided to add only distilled water.
I let you choose whether you wish to make the liquid soap with glycerin or without it, since this soap, in the end, is less aggressive than most commercial liquid soaps. Glycerin is a humectant and contributes to additional moisture and soap glide (slides easier). The quantities here won’t be absolute, but percentages and examples, as it all depends on how much soap paste you are using:
– Liquid soap with water and glycerin: 35% soap paste; 52% distilled water; 13% glycerin
Example: If you wish to make 200g of liquid soap, this means 0,35 x 200 = 70g of soap paste, 0,50 x 200 = 104g of water and 0,13 x 200 = 26g of glycerin. If you wish to use 100g of soap paste, this means 100 x (0,52 / 0,35) = 148g of water and 100 x (0,13 / 0,35) = 37g, which will give you a total of 285g of liquid soap
– Liquid soap with water only: 35% soap paste; 65% distilled water
Example: If you wish to make 200g of liquid soap, this means 0,35 x 200 = 70g of soap paste, 0,65 x 200 = 130g of water. If you wish to use 100g of soap paste, this means 100 x (0,65 / 0,35) = 185g of water, which will give you a total of 285g of liquid soap
Dilution rates for thin soap
These ratios will give you a thick soap and most likely you will need to add more water, as you may find that the soap paste is not dissolving completely. If you wish for a thinner soap – thinner doesn’t mean less quality – you can start with 1:3 dilution ratio. Why would you want a thinner soap? Well, we are almost “programmed” to use 1 to 3 pumps of a soap dispenser to wash. You won’t use less than that just because your soap is more concentrated.
For a 1:3 dilution ratio, you can use the following percentages:
– Liquid soap with water and glycerin: 25% soap paste; 60% distilled water; 15% glycerin
Example: If you wish to make 200g of liquid soap, this means 0,25 x 200 = 50g of soap paste, 0,60 x 200 = 120g of water and 0,15 x 200 = 30g of glycerin. If you wish to use 100g of soap paste, this means 100 x (0,6 / 0,25) = 240g of water and 100 x (0,15 / 0,25) = 60g, which will give you a total of 400g of liquid soap (talk about savings).
– Liquid soap with water only: 25% soap paste; 75% distilled water
Example: If you wish to make 200g of liquid soap, this means 0,25 x 200 = 50g of soap paste, 0,75 x 200 = 150g of water. If you wish to use 100g of soap paste, this means 100 x (0,75 / 0,25) = 300g of water, which will give you a total of 400g of liquid soap
These values are start values. You can add more water while making the liquid soap, register those quantities and use them later on.
Using a preservative in liquid soap can be a personal choice, but in my opinion, is a “must-have” unless you are making liquid soap in small batches. The rule of thumb is if your soap pH is 10 or above, no preservative is needed, below 10 you will want to consider a preservative. The lower the pH, the more hospitable the environment for those undesirables developing in your soap.
You also need to consider any sugars that you add to your soap. Many additives are considered “bug food” and will increase the likelihood of those undesirables developing in your soap. Proteins, some extracts, using any food product (milks, teas, coffees) as part of your dilution, etc. All of these ingredients will increase the chance of things developing in your soap that you don’t want in there.
The two preservatives that have been recommended for use in liquid soap are Suttocide A and Liquid Germall Plus. You use Liquid Germall Plus
Vitamin E, Grapefruit Seed Extract and Essential Oils are not preservatives and will not deter the growth of bacterial, mold, yeast or fungi. More information about preservatives in personal care products can be found here: http://www.makingskincare.com/preservatives/
You can add scent to your liquid soap at the end: essential oils or fragrance oils (or a mixture of both). Unlike cold process, they won’t lose strength, as the soap will be completely finished when you add them, so you can use pretty much anything you wish.
They will give your liquid soap a pleasant scent, but they are completely optional. If you have sensitive skin, you might consider skipping them. They might also cloud your liquid soap (from transparent to cloudy or “foggy”).
Use 3% of essential oils/fragrance oils of your liquid soap. For example, for 200g of liquid soap, use only 6ml.
Step 10: Making the liquid soap
Turn on your slow cooker and set it to HIGH heat. Pour the soap paste, the water or water and glycerin mixture into the slow cooker and mix gently. Let the ingredients warm up, then turn the heat to LOW. Leave the mixture like that for 1 hour, gently mixing every now and then, and gently squish existing bits of soap paste floating around.
If there are just too much soap paste after one hour, add more water and repeat the process, leaving the mixture under low heat again for one hour. Repeat the process until you are left with only some bits of solid soap paste. This part does require patience and some trial and error. After that, turn off the heat and cover the slow cooker. Let it set in its residual heat for several hours, or overnight preferably.
At the end, once completely cooled, your soap should be overall liquid and homogeneous, transparent and usually with a golden yellow color (but that depends on the oils used). Some chunks of solid soap are still expected.
Step 11: Adding the addictives
Strain your liquid soap into a bowl to catch any left chunks of soap paste. Add the fragrances/essential oils and the preservative. Mix well and pour your liquid soap into pump dispensers for immediate usage or jars for storage.
It’s usual that your soap looks beautiful and transparent when it’s still hot, and once it cools down to room temperature, or when you add your addictives, it gets cloudy or opaque. This can look like little droplets of white, white streaking or ghosting, general cloudiness or a completely opaque soap.
This is due to the cloud temperature being relatively high. It greatly depends on oils used, addictives used and it’s hard to control, as there are many variables. There aren’t two formulas that behave the same way. This article states that the simpler the ingredients with the fewest additives, the lower the cloud point temperature – fewer ingredients to precipitate out of solution. This doesn’t affect the soap quality, only its looks.
Next in this Soap Making series: How To Use a Soap Calculator
I hope this soap making tutorial has been helpful! If you have any questions, please use the comments section.