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How to pH Test Soap the Right Way & Why It Matters!

One of the common questions that come up on Modern Soapmaking, especially in hot process tutorials and liquid soapmaking tutorials, is how to pH test handmade soap. It’s easy to understand why when there is so much conflicting information on the internet pH testing soap!

How to pH Test Handmade Soap Properly

I hope to clear up a lot of common misconceptions about the why and how of pH testing handmade soap in this article, and will be including information and examples for various kinds of soap! Before we dive in, let’s review…

What is pH anyhow?

pH is a measurement of the hydrogen ion concentration in an aqueous (water) solution. Solutions with a high concentration of hydrogen ions have a low pH, while solutions with a low concentrations of hydrogen ions have a high pH.

Neutral is a pH of 7, while anything above that is alkaline, and anything below is acidic. Most people are familiar with the pH of household substances like citrus juices, milk, and various cleaning products, but just in case you aren’t, here’s a quick approximate comparison chart of common materials on a pH scale:

pH testing handmade soap typically shows a result between 8 and 10, but can creep up near a pH of 11.

As far as I’m aware (and have been able to find scientific evidence for – the important part), it is impossible for a handmade soap to fall near neutral or below without using an emulsifier to keep the soap molecules within the solution. I know that soapmakers frequently state that they can or do create neutral pH soap, but such products don’t tend to be true soap, meaning that they aren’t composed mainly of the alkali salts of fatty acids.

Sometime ago, Kevin Dunn asked the handmade soapmaking community to please send him a soap with a pH of 7 or below, and as far as I’m aware, no one was able to do so.

Important Notes about pH Testing Soap

There are two key points I want to jump into here, before we start talking about pH testing soaps.

First, it’s important to keep in mind that pH is a measurement of hydrogen ions in an aqueous solution. It is not a measurement of hydrogen ions in whatever substance you feel like measuring! Obviously, when you are looking at bar soap, it’s a relatively solid material – not an aqueous solution. In order to properly test the pH of a bar soap, you should attempt to use a solution. (We’ll get more into that later on.)

The second important note is that pH is not a direct relationship to how harsh or mild a product is (whatever that means in the first place!) When it comes to skin chemistry, a common misconception is that your skin has a pH – it doesn’t, your acid mantle does. The acid mantle can have a varying pH between 4.5 and 6.2, depending on your ethnicity, age, and gender, as well as the area of the body, the humidity, and various other factors. Your acid mantle acts as a barrier on top of your skin that helps discourage the growth of fungi and bacteria.

In general, brief exposure to slightly acidic or slightly alkaline material (like using handmade soap, which is slightly alkaline) does not harm the acid mantle. Healthy skin can rebalance the acid mantle in a very short amount of time (in as little as 15 minutes to as long as 90 minutes). Long-term or prolonged exposure (such as applying a high pH product to your skin and leaving it on for hours) can cause damage, just as exposure to extremely acidic or extremely alkaline (like sodium hydroxide) material can.

Even if you wash your skin with tap water (typical pH between 6 and 8.5 depending on the source) and no soap or cleanser at all, the pH of your acid mantle will slightly increase immediately following washing. (In a study of infants, water-only washing sees a pH rise of 1.1 while alkaline soap, like handmade soap, sees a rise of 1.2 points.) Furthermore, there are plenty of high pH products on the market that are less irritable to the skin than lower pH products! (One study found that Johnson’s Baby Oat soap, with a pH of 12.35, was the least irritating soap tested, while another soap with a pH of 9.36 was the most irritating.)

The recent onslaught of “pH-balanced” skin care products is largely a marketing ploy. So, pH should not be viewed as an indicator of whether or not a product is irritable to your skin unless it is being applied for hours at a time or has an extremely acidic or alkaline pH that could cause damage.

Well, what’s the point of pH testing soap then?

A lot of soapmakers attempt to use pH testing soap as a indication of excess alkali, and this is flawed for a few reasons.

First, unless a soap contains a large amount of excess alkali, it could test within a “normal” pH range for handmade soap (between 8 and 10). And, if given enough time to cure, lye-heavy soap could eventually test normal as carbon dioxide works its magic on free alkali. (Fun fact: sodium hydroxide + carbon dioxide = sodium carbonate, which is soda ash!)

Plus, if you pH test handmade soap fresh out of the mold the soap could be unfinished. Saponification may not be fully complete. How quickly a properly made soap saponifies depends on the oils used (or the fatty acid profile of the formula), as well as the temperature of the soap and the environment, and can range from as little as 24 hours to multiple weeks.

The second reason using pH testing soap as a indication of excess alkali  can be flawed is that soap can saponify unevenly. For instance, the middle of a batch of soap typically saponifies quicker, if gelled, while the exterior edges don’t saponify as quickly. The top of a batch of soap could be slightly more alkaline, as the water (which carries the lye) evaporates out of the soap. Or in such cases of lye-heavy soaps, the lye solution or undissolved lye crystals can concentrate in pockets or specific areas in the final soap. Unless a soapmaker pH tests soap in just the right area, they could come out with a  rating that ignores the presence of excess alkali.

Does this negate the usefulness of pH testing handmade soap? Yes and no!

It’s much easier to identify lye-heaviness through visual cues, like the presence of liquid pockets or crystallization, rather than pH testing soap. If there is an unknown liquid or substances seeping out of a soap, a pH test can help you identify if the liquid is lye solution or separated oil, fragrance, or another additive. pH testing handmade your soap to confirm a suspicion when troubleshooting is the first step in knowing how to correct it.

Essentially, pH testing your soap show an abnormally high pH, then you know you need to either neutralize or continue cooking the soap (in the case of liquid or hot process soapmaking), or rebatch it (in the case of cold process soap). To neutralize or rebatch soap, you must first figure out how much excess alkali is present – either by reviewing your procedure (hence why it’s important to check/calibrate your scale, detail your process, and use self-check measures to ensure accuracy) or titration to measure alkalinity. Scientific Soapmaking and Liquid Soapmaking are two books that detail the entire titration process!

Another way pH testing handmade soap can be useful is if you sell your soaps and want to adhere to good manufacturing processes. Conducting a pH test is one of many ways to conduct quality control, ensuring that your products fall within a specific range of “normal“. However, pH testing your soap should not be used as the sole quality control measure, as it can be unreliable.

And finally, let’s be realistic here, pH testing your soap satisfies curiosity and can be useful in understanding the chemistry behind saponification! If you ever get the urge to make multiple soaps with single oils, pH test them during the curing period every week to see how they change. Various saponified oils (and individual fatty acids) have differing pH levels, and the pH does tend to slightly drop over time.

The Do’s and Don’ts of pH Testing Handmade Soap

If you do want to pH test your soap, it’s important to start off on the right foot. When I was in the process of researching this article, I came across tons of blog posts and how-to videos out on the internet that gave instructions for pH testing handmade soap. Here’s a rundown on some of the most common instructions I found:

Using Tongue Testing or Zap Testing to Check Soap Alkalinity

An extremely common recommendation I found as a method of checking the soap pH is to touch a bar of soap to your tongue. If touching the bar of soap to your tongue zaps similar to touching your tongue to a battery, it indicates a soap is lye heavy. Obviously, this doesn’t actually indicate the pH level of a soap, it simply indicates the presence of free alkali.

I know plenty of soapmakers who use this method in their process, and while I won’t argue its efficiency or efficacy, I will argue it’s safety. If a new soapmaker comes across this advice and has not yet familiarized themselves with the appearance of lye heavy soap, tongue testing could result in serious injury.

Just say "no" to tongue testing or zap testing!
Just say “no” to tongue testing or zap testing!

Additionally, if you are a soapmaker in business, tongue testing is a liability, safety, and GMP (good manufacturing practices) nightmare. GMP encourages robust testing and quality control among other processes, and while tongue testing accomplishes the job, it is unhygienic and dangerous. If an employee sustains an injury due to poor manufacturing practices, the liability falls on you, as the owner and creator of the procedures and manufacturing process. No, thanks! There are much better ways to pH test your soap.

Using pH Strips to Test Soap pH

The next most common method of pH testing soap I found online was using pH strips. Most of the tutorials and how-to instructions I came across were a variation of the following:

  1. Place water on the surface of the bar of soap.
  2. Rub the water onto the soap until it lathers.
  3. Dip the pH strip in the bubbles.
  4. Check the pH strip against the chart included.
Using pH strips directly on a bar of soap can give you an inaccurate pH reading that is so far off you might think your soap is neutral!
Using pH strips directly on a bar of soap can give you an inaccurate pH reading that is so far off you might think your soap is neutral!

The first problem with pH strips is that the nature of soap interferes with the indicator dyes used to manufacture the strips, which can throw the reading off by several points. (In my testing, pH strips gave me a reading varying from a pH of 5 to a pH of 9 – a huge range!)

The second issue with this method of pH testing soap is that the process of putting water on the surface and rubbing it until it lathers creates a huge variable. How much or how little soap is dispersed in the water can affect the reading of the pH. None of the instructions detailed creating a definitive solution containing a specific ratio of soap to water. Some of the tutorials even negated specifying what kind of water to use! (As we mentioned earlier, tap water can vary a lot and throw off the readings.)

If pH strips are all you’ve got and you are eager to pH test your soap, using a specific solution and higher quality pH strips will help get some of these variables under control. (We’ll talk about how to do that in a minute!) That being said, using pH strips is not the most ideal method of checking a soap’s pH.

Using Phenolphthalein Drops to Test Soap pH

Phenolphthalein drops are most commonly recommended for testing liquid soap and hot process soap during the cook to identify whether the soap is “done” or if the soap needs to be neutralized. And while phenolphthalein drops can kind of serve that purpose, most of the tutorials and instructions I found directed you to place the drops directly on the soap. Pure soap, whether it’s liquid soap paste or hot process soap, isn’t an aqueous solution. And phenolphthalein drops, like other methods for pH testing soap, should be used in a solution.

Phenolphthalein drops should be using in a solution rather than directly on soap, and can only tell you so much.
Phenolphthalein drops should be used in a solution rather than directly on soap, and can only tell you so much.

The main issue with phenolphthalein drops is how they work as a pH indicator. When added to a solution, phenolphthalein changes from clear to pink, depending on the pH of the solution. The initial color change from colorless to pale pink happens at a pH of 8.2, and deepens to a dark fuschia as the pH rises to 9.8. If used in a solution with a higher pH, they remain bright deep pink.

Phenolphthalein drops indicate a solution's pH by changing from a colorless liquid to a deep pink. The color indication ranges from a pH of 8.2 to 9.8, and does not change outside of that range.
Phenolphthalein drops indicate a solution’s pH by changing from a colorless liquid to a deep pink. The color indication ranges from a pH of 8.2 to 9.8, and does not change outside of that range.

This color change can be useful if you are wanting to bring the pH of a product below 8.2, which often requires the use of weak organic acid, such as citric acid. It can also be useful to titrate a soap solution to measure alkalinity, which is the case in common instructions for neutralizing liquid soaps.

However, pure soaps as a general rule have an alkaline pH, ranging from 8 to 10, so phenolphthalein drops don’t necessarily indicate whether a soap is done cooking or safe for use. A liquid soap with a pH of 8.1 and a liquid soap with a pH of 8.3 (which crosses the color indication line for phenolphthalein drops) isn’t going to perform wildly different as a basic cleanser. Plus, a soap with a pH of 10 (which is normal) will test exactly the same as a soap with a pH of 13 (which is not normal.)

How to pH Test Handmade Soap

Now that we’ve talked about all the issues with pH testing soap, let’s get down to business with how to pH test soap in the most ideal way.

To do this, let’s turn to a source for professional standards, ASTM International (American Society for Testing and Materials International). They are an international organization that develop and publish technical standards for a wide range of materials, products, systems, and services. And luck would have it that they have a standard for exactly what we need: ASTM D1172 – 15 (Standard Guide for pH of Aqueous Solutions of Soaps and Detergents).

Now, I would guess that most of us do not have the fancy equipment that the standard dictates for pH testing soap. (It recommends using a Fischer Accuphast combination electrode or Orion Ross Sure Flow electrode.) However, it is possible to follow the standards in procedure relatively closely!

To put this to work, I’m sharing pH testing results using a variety of methods/pH testers on a bar of soap that is three days old (relatively fresh, but should be mostly saponified at this point). The bar of soap is from the middle of the loaf, and partially gelled. There are no obvious signs of separation or excess alkali.

Here’s the list of pH testing materials:

The first steps described in the standard is preparing the reagent, listing distilled water or equivalent, by removing the carbon dioxide by boiling or purging with carbon dioxide free air. The standard instructs to protect the distilled water with soda-lime or soda-asbestos while cooling and in storage. The next steps in the standard explain making a soap solution, and bringing it to an accurate temperature for pH testing.

My goal here is to follow the standard as closely as possible while still being practical for a handmade soapmaker, so let’s dive in:

First, I boiled my distilled water, which will serve two purposes: help eliminate carbon dioxide and help dissolve the soap. Next, I shaved pieces of the soap from the side of the bar, from top to bottom, using a paring knife, into a clean disposable cup.

I’m aiming for a 1% soap solution, meaning 1% of the solution is soap and 99% of the solution is distilled water. To make it easy, I weighed approximately 1 gram of soap and 99 grams of distilled water on my American Weigh Scale (AWS-100). (I use this scale more often for blending essential oils and other tiny tasks, it’s pretty handy and affordable!)

Weigh 1 gram of soap for pH testing on a gram scale.
Weigh 1 gram of soap for pH testing on a gram scale.

Next, I added the distilled water, with a temperature reading of about 70° C (158° F), to a glass mason jar and then added the soap shavings. (The distilled water is still hot from boiling! As I mentioned, it was boiled directly beforehand.) Using a mini-whisk, I stirred the solution until the soap dissolved.

A prepared 1% soap solution ready for pH testing!
A prepared 1% soap solution ready for pH testing!

The standards mention that you should conduct the pH test at 40° C (plus or minus 2° C), which is about 104° F and that the solution should be rapidly cooled. To do so, I placed my mason jar is an ice bath and kept an eye on the temperature while I prepared the pH testing materials.

Each one of the pH testing materials I used came with varying levels of instructions for accurate readings, so I defaulted to each individual one for instructions. For instance, some pH testing strips say to submerge the strip for 30 seconds while others say to “dip the strip” in the solution.

Here’s the results of pH testing my soap with various methods:

The Hydrion Paper Strips were obviously inaccurate, as we know that cold process soap cannot naturally test at a pH of 7.
The Hydrion Paper Strips were obviously inaccurate, as we know that cold process soap cannot naturally test at a pH of 7.
The Hydrion Plastic Strips were not any better (typically, plastic strips are little bit better). It was impossible to determine if these strips were indicating a pH of 5 or 6, but we know that neither is accurate.
The Hydrion Plastic Strips were not any better (typically, plastic strips are little bit better). It was impossible to determine if these strips were indicating a pH of 5 or 6, but we know that neither is accurate.
Lab Rat Supplies Paper Strips were realistically closer, reading a pH of 8. However, since this soap is fresh, it should test higher.
Lab Rat Supplies Paper Strips were realistically closer, reading a pH of 8. However, since this soap is fresh and contains the blend of oils that it does, it should test higher.
The leader of the pack was found in Lab Rat Supplies Plastic Strips, which gave a pH reading of 9, which seems both plausible and realistic for a fresh bar of handmade soap.
The leader of the pack was found in Lab Rat Supplies Plastic Strips, which gave a pH reading of 9, which seems both plausible and realistic for this bar of handmade soap.
Even though phenolphthalein isn't very useful for pH testing, I did want to share what it would look like if used. The color of this photo is little off, but the solution definitely tested a relatively deep pink, as it should.
Even though phenolphthalein isn’t very useful for pH testing, I did want to share what it would look like if used. The color of this photo is little off, but the solution definitely tested a relatively deep pink, as it should.
Next, I wanted to try using an Universal Indicator solution to test handmade soap. Like the other pH strips, this indicator has a range of pH 1 to 14, but the color shift can sometimes be hard to differentiate.
Next, I wanted to try using an Universal Indicator solution to test handmade soap. Like the other pH testing methods, this indicator has a range of pH 1 to 14, but the color shift can sometimes be hard to differentiate.
The 1% soap solution tested as a pH of 10 using the Universal Indicator, which is right where it should be! If you want to try a fun science experiment with your kidlets, red cabbage juice is a universal pH indicator, too!
The 1% soap solution tested as a pH of 10 using the Universal Indicator, which is right around where it should be. If you want to try a fun science experiment with your kidlets, red cabbage juice is a universal pH indicator, too!
The Apera pH Meter tested exactly where I expect, with a reading of 9.6 to 9.9 depending on the temperature. This particular meter supposedly temperature compensates, so I wanted to test that and it does a pretty good job.
The Apera pH Meter tested where I expect as well, with a reading of 9.6 to 9.9, depending on the temperature. This particular meter supposedly temperature compensates, so I wanted to test that and it seems to do a pretty good job.

Alright, so pH testing soap is all sorts of crazy…

After all this research and work, I have a few key takeaways about pH testing soap, whether it’s cold process, hot process, or liquid soap. Here’s the quick hit list:

  • pH strips are terrible. Most of the pH strips I have used (both for this article and in the past) have been wildly inaccurate. The good news is that lab-quality plastic strips don’t seem to do too bad off a job, if your curiosity is killing you.
  • pH testing soap is largely inaccurate. Bar soap, liquid soap paste, and hot process soap are still just soap, and even when you make a soap solution, you are creating a colloid (where tiny little soap molecules are suspended in water). Since pH testing relies on an aqueous solution, it’s difficult to get an accurate reading regardless of how you do it.
  • If you want to pH test your soap, some methods are more accurate than others. Both the universal indicator and the inexpensive pH meter did a decent job of giving a pH reading, especially when compared to the wide range of readings from pH strips. If I had to choose one method of all the ones I’ve tested, I’d stick to the pH meter (especially as it would be useful in lotion making too).
  • No matter the method, pH testing soap isn’t as useful as many soapmakers think it is. Your soap’s pH doesn’t saying anything about how mild or gentle it is, since it’s a wash-off product. While pH testing your soap can be helpful as a diagnostic tool in the troubleshooting process, it shouldn’t be relied on as the sole method of identifying problems with a batch.
  • Which brings us to the final takeaway: if your soap pH reads higher than it should, give it time. I’ve witnessed too many soapmakers throw away batches of soap (both liquid and bar soap) because their pH test came out with a 9, 10, or 11. Before you make any drastic moves, give the soap a little time to finish doing it’s thing. And then pH test your soap again.

When it comes down to it, I know that soapmakers are going to pH test soap however they prefer (including that pesky tongue test!) However, I hope by working through the rundown on pH testing handmade soap, I’ve given you some food for thought and other options. Leave a comment down below, and let me know if you learned anything new or what you think!

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130 Responses

      1. Thanks for the great work Ma’am, I Love soap making and ‘ll like to eat, eat and sleep soap making like you do. Have never made soap before please I need your help on this. I LOVE SOAP MAKING PLEASE HELP ME.

        1. Valentine, while essential oils are used as fragrance in soapmaking, they are distilled from plant material, as opposed to fragrance oils that are blended from various natural and synthetic chemical compounds. Fragrance oils allow for greater variety

          Olive, castor, and coconut oil are true oils (fats). They are often called base oils in soapmaking.

      2. I find this article very informative and helpful. Thank you!

        My question:

        “Furthermore, there are plenty of high pH products on the market that are less irritable to the skin than lower pH products! (One study found that Johnson’s Baby Oat soap, with a pH of 12.35, was the least irritating soap tested, while another soap with a pH of 9.36 was the most irritating.)”

        -I, too, had a misconception that hand made soap with pH of 8-10 causes skin irritations; however, you suggest it’s unrelated. (which is wonderful, I got discouraged in making soap because I read elsewhere that pH 8-10 is what a handmade soap would be and thus it’s the cause of the skin irritation) What could be the cause of the slight itchiness when using handmade bar of soap? How could I prevent it? (I know there could be many factors such as oils, fragrance, essential oils, etc.) There must be some obvious thing that cause this…

        Thank you again,

        1. With such a generic example, it’s impossible to say, Nicole. A few possibilities come to mind:
          -An allergy to one of the ingredients
          -Incomplete rinsing, leaving residue on the skin
          -Poorly made or very fresh soap that contains unsaponified lye

    1. I have been reading and researching homemade soap making and have bought everything I need to start making my own soap. One of my main concerns was the PH levels in soap. I am sooo happy that I didn’t waste a dime on those strip testers. Your article is so enlightening and gave me more to consider. Thank you for your research as it is much appreciated.

    2. Very interesting… question … on saying the inexpensive PH tester is closest have you tested any of the testers on looking at the tester it says 44$ but I see others too and rather cheaper do you know if those would be as accurate like on Amazon the VANTAKOOL PH Meter 0.01 is under 14$

      1. Hey, Susan, we don’t have the means to test every meter on the market, so I cannot comment on the one you looking at. If it has favorable reviews, it might be worth a shot, but you often get what you pay for with these things.

    3. I am so happy I found this article because there is so much conflicting information on the internet, and lots of it from popular soap sites. The tongue testing thing really bothers me. One of the biggest popular sites actually tells people to do this and I just did not understand why anyone would do that. It is unethical and just downright disgusting. Your information is totally accurate and easy to understand. We are lucky to have someone like you willing to share this information.

      Thank you for your wisdom. 🙂

    4. Could you measure millivolts instead of pH to test for saponification?
      I too have found pH testing unreliable. The tongue test seems the most reliable but unsafe. The tongue test implies that there is a voltage difference created by the unreacted lye and soap. “zapping” that acts like a tongue on a battery. I used a $5.00 voltmeter from Harbor Freight set on the 20 mVDC scale. I measured a voltage difference of 23 mVDC when I first poured my soap into the mold. When I removed the soap from the mold and dissolved a small portion in water, the reading was 13 mVDC. When I tested “cured” soaps, I found the voltage difference to always be in the single digits. I have not done this experiment in a controlled manner – yet – but the preliminary investigations show that this might be a promising way to test for saponification.

      What do you think?

      1. Your tounge won’t feel a voltage difference in the range of 10 mV – it does feel the current flowing from one pole of a battery to the other pole. Think of static charge (can be in the range of hundrets to thousands Volts) – you don’t feel it at all until you discharge yourself at another object…
        The sensation of a negative “zap-test” (free alkali) MAY feel similar as nerve ends are stimulated to fire signals to your brain but I’m sure the underlying biochemical mechanism is different.

        10mV usually fall quite deep into the range of inaccuracy with these cheap meters (read the specs of yours), also you don’t specify the points where the voltage difference was measured between – guessing you just stuck the two probes into your soap you won’t imo get any meaningful readings.

        It may be possible to make a soltion as described in the article and measure conductivity (with a fixed distance of your probes) to get an indication of free ions – but again I wouldn’t expect a meaningful result in terms of free alkali because the solution is full of “soap-ions” and whatever ionic ingredients you’ve used anyway.

        I’m a hobbyist in electronics and even more in soaping, have licked the first of the few soaps I made but as long as the outcome looks and feels smooth whashing it, I don’t care about pH – and for sure will not stick my tounge on anything with cavities and/or crystals in it. 😉

        Having worked with rather cheap electronic pH-meters for a while in hydroponics – they need good care (storing the probe in a special solution) and regular calibrating – though never fully trusted them.

        Thanks Kenna for your insights, I love your scientific approach while your articles are still easily “digestible”.

    5. Thank you for doing the testing and give us good scientific explanation about the pH in soap. I am going to get the pH meter to observe what happens through time as the soap cures (just curiosity). I am also curious if by increasing the super fat, the soap pH will go down a bit

    6. Good day,
      My name is Dianne, email address diannesf10@gmail.com.
      I am super glad to have found this site, your information and the reference sources information, are tremendously insightful.
      Like you I found Failor’s book to be intimidating and the one recipe I tried with it, came out very thin and not as soapy as I thought it should be. I have put that book so far, I don’t even know where it is.
      Thank you so very much for simplifying things for me. I think I can try a hot process soap now, and I will.
      Thanks again.

  1. I made hot process soap last night for the first time, and my tongue still hurts from being zapped. Thank you for teaching me to not do this again. I appreciate it!

    1. Ick! You may want to call your doctor and see if you need to get it checked out. I’m sorry to hear this happened to you! You are very, very welcome, and I hope this article helps!

  2. Beautiful, well researched article Kenna. I am a chemist, but I sure learned a few things from your article! Well done.

  3. I was waiting for that article quite some time and now that I’ve read it I’m glad we have the same point of view on the specific matter. It is well written and once again I think your audience will get some valuable information on the pH side of handmade soaps.

    My only remark is on the zap test method. It can be done without any serious injury even from a new soapmaker.

    It was also shown by a video with Kevin Dunn, where someone can wet his finger in water (or with his saliva) and then rub this finger on a soap bar at an area that is suspected for exceed lye. Then this finger with the little soap aqueous solution on it, can be very slightly touched by the edge of our tongue… If there is active lye, then we will understand it by a slightly voltage feeling and we can put our tongue under a tap with running water.

    I’m not forcing anyone to do this test, but if they feel like they want to try it, it not so dangerous. Zap test is not something like this for sure: http://assets.nydailynews.com/polopoly_fs/1.100027.1324488107!/img/httpImage/gal-watn-acs-soup.jpg


    Well done once again for the info you gathered!

    1. Thanks, Nikos! I won’t lie – I thought of you when I hit publish on this one. 🙂 I appreciate your input in this community and on my content, and always look forward to what I can learn from you. (Also, I giggled at the photo. Yes, zap testing is definitely not the same!)

  4. Amazing Kenna, thank you! I conducted tests at different intervals with each of my batches and always found that it improves. The information on this is usually so unsubstantiated that this is incredibly refreshing.

    1. Thanks, Mathilde! Yes, the unsubstantiated information around the internet when it comes to anything soapmaking is a surefire way to get me into research & write mode. 🙂 I’m so glad that you enjoyed it!

  5. excellent article. Would have been fun to be a “fly on the wall” and see this in action. I used to use pH strips and had some reasonable accuracy, but now that I am going into business, and it is much more important for GMP, I think I will invest in the meter. Have you tested that same soap solution idea at 5 or 6 weeks of cure time? Would be interesting to me to see how quickly it changes, and the final pH. thanks!

    1. Hi Kirsten! I have done this in the past, but this was sometime ago and not documented. (Well, it is, but in one of my soap notebooks, so good luck finding it. LOL) I have been quite happy with this pH meter, and it’s nowhere near as expensive as other models. I expected it to be horribly inaccurate, but I haven’t found that to be the case. 🙂 Thanks for reading!

  6. Kenna,
    thank you for all the research you have done for us and showed visually in great detail. You are fabulous in so many ways!
    Bottom line in regards of ph- testing, which one would you recommend for CP soap?

    1. Thanks, Helena! Personally, I would default to use this pH meter as it was relatively inexpensive and decently accurate in comparison to other methods I tested.

  7. Thank you Kenna. Excellent article. I envy you the fun of testing it all. I had been wondering just how to test properly, and now I know both how to do it and really, not to sweat it. I have a batch that’s lye heavy (I forgot to add one of the oils) and I’ll try that against other soap that I made properly.

    1. The biggest problem with testing like this is remembering to take photos for the article! Haha. 🙂 Definitely use that known lye heavy soap to compare. If you have time and the inclination, I’d save one of those suckers for a few months and then pH test it again. It’s fascinating! Thanks, Lisa!

  8. Hi,
    Thanks for a great post on pH. However, I would differ on the use of test strips. We are lucky in my company that we have a lab with two pH meters, test strips, and Quality Manager with Honours Degree in Chemistry. Plus, I have spent 30 years working globally as a consultant training laboratory analysts.

    From our experience, lab quality test strips can provide reliable results. One of my lab analyst training sessions is to have students compare test strip results and pH meter results. In our own lab, we often compare the meter and test strip results. Obviously, we get decimal point accuracy with the pH meter, but find the test strips useful for quick tests.

    Test strips that are less than lab quality are useless.

    The other point I will make is that pH meters can be difficult to maintain and calibrate, and the probes have a limited life. This is something not appreciated by novices. In my training of laboratory analysts this is something we spend a lot of time on.

    Dr. Mike Thair
    Managing Director & Chief Formulator
    Indochine Natural Sdn. Bhd.

    1. Thanks, Mike. Yes, as I mentioned under the takeaways, lab-quality strips seem to be more reliable. I don’t find pH meters to be difficult to maintain or calibrate, simply a normal process of the work, but yes, they are more work than using pH test strips. Thanks for weighing in. 🙂

      1. If you buy a pH meter from Amazon, or another source where people can leave reviews, you do quickly learn that they have a somewhat limited lifespan (at least the probe part). I researched the heck out of them before I bought, and finally just tried to hit a happy medium between good quality and understanding that I would eventually need to replace it. This is true of lab quality ones as well. I’ve done work in a few college labs, and the pH meters were always breaking down. Just the nature of how they are built and how they work I guess.

  9. Thank you SO much, Kenna, for all the time and hard work to boil it all down to this excellent article. I happen to be a “majority of one” that uses lye-based shampoo bars and liquid soap/shampoo, on a forum with a “concensus mentality” that says “lye-based soaps are BAD for hair and scalp.” With your permission, I’d like to share this article with the group. ?

    1. Hey Cee! You are welcome to share this article, however, I do tend to agree with the thought that high pH products can be rough on the hair. The reason for this is because hair is made up a little differently than skin. It doesn’t have a protective acidic layer that rebalances itself like the skin does with the acid mantle. It’s been several years since cosmetology school, but here’s what I remember:

      The outside of hair is the cuticle, which is made up of flat scales that protect the hair shaft. Alkaline products (like handmade soap) can contribute to changing the protein structure, lifting the cuticle scales, and increasing the density of the hair shaft through swelling. Hair is already really vulnerable when it’s wet, and alkaline products can increase the risk of breakage and frizz from the swelling & cuticle friction.

      I’ve read varying studies about what the “safe” cut off pH is for preventing cuticle damage, and there isn’t a clear consensus, as it largely depends on the person and how they treat their hair in the first place. Since I already subject my hair to a lot of abuse through bleaching & coloring and have thick coarse hair, I personally stick to a pH range between 4 and 7.5, and do not use soap-based shampoos. I know plenty of soapmakers who formulate them and use them just fine – different strokes for different folks. 🙂

      Here’s a couple studies:
      The Shampoo pH can Affect the Hair: Myth or Reality? (2014): https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4158629/
      Essentials of Hair Care often Neglected: Hair Cleansing (2010): https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3002407/

  10. Very interesting article. I don’t think I have every seen pH testing soap so well covered.

    I will continue to use the time-honored “pesky tongue test,” lol, but enjoyed learning what you presented.

  11. Bless you for writing this.

    Bless you also for pointing out that soap dissolved in water is a colloidal solution!!! This is soooo important to understanding pH readings.

    I don’t think a majority of folks who drag pH strips across the top of a wet bar are eager to change practice, but at least I have an easy to read and well-researched article to point them to!

  12. Kenna, thank you for taking the time to write this informative and well researched article. I’ve never been a fan of the tongue test. Yes, I understand that there is no need to French kiss your soap, but I always thought the test was still unprofessional. It would be tough to explain to an insurance company, or an FDA official.
    I’ve known the PH strips had their limitations also.
    It looks like a decent Ph meter can be had for about $20.00, and would be worth the investment. They do need special care.

  13. Thank you for your response. I used to color & perm but at age 45 my 20-Y-O daughter suggested I stop that and let my “natural beauty” come thru. Now, at age 74, after using lye-based homemade shampoos for 14 years, I have virgin dark ash brown hair with only a single strand of grey here and there. It did take a bit of time to get used to, along with vinegar/beer rinses, conditioner, etc, but it’s very healthy now and I don’t use anything except a drop of Argan Shine after styling. 🙂

    1. This might be fantastic for your hair. I’ve seen people defend the use of CP soap on hair vehemently. If its working for you, that’s awesome. The problem is that it doesn’t work for everyone. In fact, I’d argue that it doesn’t work for most people. And for folks who don’t understand that, they think THEY are doing something wrong with their formulation, rather than that its just not a good fit for their hair type. This post is yet another well researched piece on why its just not a good fit for everyone (it wasn’t for me – though it took several months for the gradual damage to really start to show). http://swiftcraftymonkey.blogspot.com/2010/04/why-cp-soap-doesnt-make-great-shampoo.html

  14. Wow! This article is amazing!!! Thank you so much. 🙂

    I wish this article would have been around when I began testing the PH in my soaps 3 years ago. Best answer/solution I could find at the time (2014) was using the PH strips or forking over $300+ for a PH meter. Or so I was informed from other soap makers I asked. I chose the 0-14 PH strips and usually got a reading between 8.5-10 PH. If I got a 10 (at the time as a new soap maker), I went back to reformulate my recipe. Not that 10 isn’t ok. I just wanted my soaps to be between 8.5-9…that was my goal at the time. Once I consistently reached that goal (consistent to me = 10 x or more), then I stopped testing due to ongoing, repeated results.

    About 4-5 months ago, after taking your formulation class, I reformulated my recipe to accommodate both different ingredients and different saturated to unsaturated ratios, and to create more intricate designs I wanted. I changed from a 60:40 (sat:unsat) to a 45-50 (sat) : 50-55 (unsat), depending on *which* saturated fatty acids I was working with in the recipe. So far, my PH hasn’t changed from the 8.5-9. So now you have me curious and adding the PH meter to my Amazon cart, lol.

    To further dig deeper into this curious rabbit hole I’m going into, I recently started experimenting with fast-tracing FO’s…all the ones that seize and rice a soap batter (that is 45% sat.: 55% unsat.)! Now you have me wondering what my PH is when I make a test batch of either of my recipes, leave them at 7% SF at a 33% lye solution versus the workaround I found using a fast-tracing FO’s with a full-water lye solution (0% discount). From everything I have learned from you so far, I suspect the PH in the full-water soap to be much lower than the soap with the 33% solution. I am testing this so to find out the exact turn-around time and chemical differences for a batch using a high-tracing FO (and comparing to an FO that behaves, like OMH), and of course to satisfy my own curiosity. I am getting this new “toy”, the PH meter, to find out if there is in fact a large difference, and for how long that difference is from the minute I unmold to the day the soap stops losing water weight.

  15. Hats off to you for the amount of time and hard work you do for the soaping community!!! And many many thanks for “feeding my hunger” when it comes to soap chemistry. You are awesome!!!

  16. Hi Kenna, I am still researching soap making I haven’t started to make it yet. This article has so much information that will help when I start to make soap so thank you very much for doing this research for me (one less thing to research). I can’t wait to start to make soap, but is it ok to start with MP (melt and pour)? It seems so much easier to make than cold/hot process.

    1. You sure can start out with M&P. A lot of soapmakers do! It helps you get used to the pouring & molding process before you delve into more complicated recipes and lye. Just make sure to look at the ingredients in you M&P base.

    2. Kenna,
      Thanks so much for this article! I have a question. I hot process my soap and typically use pH strips to test whether the soap has finished the cook. I’m not really looking for a specific number, just that the soap is no longer at 12-14 and as a double check that it’s reached “Vaseline stage”. I use distilled water and with my gloves on, take some of the batter on a fingertip with a little distilled water, rub together between two fingers to get some bubbles to test. Only on a few occasions have I found that the soap needed a little more time (getting that dark purple color). Do you believe pH strips are accurate enough for this type of test? Or do I really need to measure out 1%? It seems so consistent to me, with earlier “stages” always being purple (I’ve been testing a lot throughout the cook, because it’s fun and I’ve recently delved into milk soaps which cook so much faster) and “Vaseline” resulting in green (8-10), that I’ve assumed the cheap plastic pH strips “accurate enough” for this application. Thanks!!!

  17. Thank you very much for this post! I just completed testing some of my soaps using the Apera test meter and your instructions. Worked perfectly for me with great results.
    My question is regarding your comment that someone had asked the soap community for a soap that was 7 ph and none were received. How is it that there are so many “natural” dog soap bars on the market if it’s not possible to make a bar of soap at 7 ph? A lot of the ingredients that I see in these soap bars include the same items that are used in cold process soap. In my quest to create my own dog shampoo, I found Earthbath who offer this product at “as close to 7 ph as possible”. Ingredients include: Purified water, colloidal oatmeal (3%), renewable plant-derived & coconut-based cleansers, organic aloe vera, vitamins A, B, D & E, glycerin, allantoin, natural preservative. They call it “natural” but how natural could “coconut-based cleansers” be? Would love to know your thoughts on this. Thank you very much!

  18. Hi Kenna,
    Do I do the PH test after unmold the soap and cutting it directly (before curing it), or leave it for a Specific Period and then test ?
    What is the most accurate way to measure the PH of soap?

    Thank you so much

  19. Kenna, Thank you so very much for all your fantastic research! Thank you for sharing so generously as well. I am definitely looking forward to documenting some comparisons on some of my recipes & how ingredients may affect pH. So excited! I love the links to extra articles on pH/shampoos, etc. Right up my alley 🙂 I love the challenge ~ Have a great day!

  20. Great article !
    What are your thoughts on the Macherey Nagel Ph-FIX 7.0-14.0 test strips for soap testing. I have done the slurry method on my cold process soap with distilled water. Seems to be accurate .
    Thanks, Karen

  21. I’m confused.

    If it’s a tonne of effort to test, half the strips are innaccurate, and a soap with a PH of 12 is perfectly okay, why should I bother to test the PH?

    1. That’s kinda the point. 😉 I know that it’s been ingrained in soapmakers heads that testing pH is important, but it’s really not a good indicator for anything and a lot of the methods that are readily used aren’t all that accurate. If folks do want to continue pH testing, my goal was to show what methods are viable. The information is also applicable to other formulations, such as a lotion, where pH can and does matter. 🙂

  22. It’s important to make the distinction between testing pH of the soap plus any free alkali OR just the free alkali. All homemade soap is basic (above pH 8)so pH paper of soap in water will always show alkalinity. The ASTM you referenced shows this but NOT free alkalinity. To measure free alkalinity just need to dissolve the soap in alcohol, which ties up the soap leaving any free alkali to change the color of phenolphthalein. Kevin Dunn details this procedure in his book.

  23. Hi Kenna, I’m new to your website and have found your info very helpful. I did not read all of the comments regarding the issue of ph testing so I hope I’m not being redundant. My question is, if my soap is not lye heavy, how long does CP soap really have to cure? The standard seems to be 4-6 weeks but why? How do I know if it’s ready to sell at 3, 4, or 6 weeks? Is that curing period related to the ph or lye “content” or some other factor. Soft oil sops obviously need longer to cure purely for the quality of the bar. But hard oil soaps? What is the bottom line?

  24. As a newbie, I am sort of confused. Not about the PH testing, which I expected would be difficult and unaccurate anyway. But the PH of the soap itself. I though a hot process soap could be added acids to go down to slightly acidic. But now I’m confused, can’t a soap go below alkali? I have not tested myself with adding acids to HP soap, since I’m a total newbie and have not tested too much yet.

    I realize that alkali soap is not harmful for your skin. But I have read that it is harmful for your hair. And I believe that. I will come back to it. So when making a shampoo bar, the hair is important and not the skin. I have used my cold processed bar soap as a shampoo sometimes. And what I realized, is that it definately was quite a volume shampoo! I got fluffy and great hair! But, when I read about it, it is because the shells on the hairs are wide open because of exposure to an alkali substance. So they said hairs need slighly acidic shampoos not to be damaged in the long run.

    And why do I believe that? Because I have done natural dyeing of wool twice. Yes, only twice, but I have read a lot about it. I like to do research. But what I anyway discovered myself, and also the same as I have read, is that wool don’t like alkali solutions. The wool will be damaged and brittle. And that happened to me the second time. The wool became very brittle. The first time, I dyed with rhubarb leaves, which are higly acidic (oxalic acid). The wool became shiny and soft afterwords. And wool is the hair of the sheep, right. So not very different from our hair. So I am 100% convinced that regular handmade soap is harmful for your hair. I have short hair, and fat hair, so not a big problem. But if you have long and dry hair, I think it could be disaster in the long run.

    I know that the only way to lower PH, if any, is to make hot process (adding acids to cold process without adding more lye to counterbalance it will only result in more superfat, or if you add acids and more lye, the ph will be the same in the end).

    I actually want to make a shampoo bar, just for my personal use, and to learn for the future. Is there any way of making a below neutral bar of handmade soap?

    1. I just posted a comment about pH testing on soap. I have not seen a soap below 8pH. And yes I fully believe homemade soap damages and strips your hair fibers. I don’t see why people use it then follow with an apple cider vinegar rinse. At that point they should use regular shampoo. As far as making soap more acidic, how could you since by nature soap is..umm..salty.. I think we should embrace soap’s natural pH. My soap tested (in a regulated LABORATORY) at an 8 pH which is beautiful! It’s from 2 week old HP 100% coconut oil soap. I think the author’s pH strips were not certified for laboratory use, or expired.

  25. :: Bows to the master::
    I’ve been on another, er, well, shall we say “Royal” soapmaking blog, because it came up first on Google. I know – dangerous. Anyway, I’d been pretty much taking their word as gospel, and I’m sure most of it is perfectly wonderful. But then I ran across a full article on pH testing, and it didn’t ring true. I got my first chemistry set in elementary school, and got my first lectures on pH testing from my highly-degreed chemist grandfather. It didn’t make any sense to me at all to test one tiny spot on the outside of a bar without any idea of the solution!
    Thank you so much for making good, sciency sense. I have been led to believe that the FDA requires pH testing for soaps sold as cosmetics, and now I have solid thoughts about how to go about doing that if necessary. I’m new, with big ideas and two batches under my belt that are still curing lol.

  26. Hi! I work in a hospital laboratory that uses the Hydrion strips. We have large strips that test a broad range, then smaller strips that narrow down the pH. We use them for body fluids, not soap obviously. I took a nip of my soap in today, set up two controls (control 1–known control of 4.0pH and control 2–our deionized water with a 7pH) and two soap samples. In one plastic tube I used 20micrograms soap to 10mls of water, the other was 10mgs soap to 10mls water. The controls came in perfectly. Both soap shard emulsions came in at a pH of 8. This is from two week old hot process soap. This is very accurate. The Hydrion strips DO work.

  27. I’m a 73 year old man that wanted to learn how to make soap that would be the favorite of my family and grandchildren. Nothing commercial. I spent ten years experimenting the degree of which started with making my own lye from the ashes of burned oak to heat my home. Very involved informative, and difficult. That aside, the end result was simple and perfect. Coconut oil, pure water and commercial sodium hydroxide. Record weight of oil (my batches are exactly 2500 grams), divide the weight of oil by 3 to determine the exact amount of pure water in grams, multiply the weight of oil by 0.1805 to determine the exactamount of technical sodium hydroxide to use in grams. This will result in coconut oil soap with about 5% of the coconut oil not made into soap but still remaining. PERFECT.

  28. My testing involves (in private) saying those really bad words I learnt while serving aboard diesel submarines in the early 60’s which I had never heard before, then privately expressing them today, then pressing the lightly moistened soap onto my tongue and judging the effect. If there is a caustic or other burning effect the soap is bad, useless and discarded.

    1. Hey there, lakshitha,
      It’s almost impossible to know what’s going on with no detail about your recipe and process. You could be over doing it on additives or you could be soaping a high stearic acid formula at too low of a temp. Are you using one of our recipes?

  29. I am super new at making soap. In fact, I just cut my first bar of HP soap yesterday. My question is, how do I know if my soap is “done” and it’s safe to use? My kids are super anxious to try our new soap, but I’m worried that it’s not ready. How do I know without doing that zap test thing? I really don’t want to do that. Does PH testing reveal there is still lye in your soap? Yes, I read the article, but a lot of it was over my head 🙂

    1. As long as the soap is uniform in color and texture throughout, pH testing can be an indicator if it’s “done.” only by whether or not there was the proper balance of lye used in the first place to saponify the soap. Done is kind of a misnomer when it comes to hot process soap, as a majority of saponification happens during the cook. However, it’s still advised to cure HP soap for at least two weeks to let it mellow out, let excess water evaporate, etc. I don’t agree with folks that say HP is ready to go straight out of the crock – sure, it should be mostly safe and okay to “try”, but I wouldn’t want to use it constantly until it gets a bit of a cure on it for the molecular structure to settle out.

  30. Informative and clear article – thanks!
    Despite using Soapcalc and a superfat of 7%, my HP soap made yesterday looks crumbly today, so I am querying pH. I shook a bit of soap in some distilled water at room temp and using a swimming pool pH testing kit – a couple of drops suggested pH of 9 but that is as high as the indicator goes, so I thought I would look online for answers.
    This is just the information I was looking for (and more).
    Wondering – this soap was made with beer as the water component – yesterday’s search told me to boil the beer to get rid of the alcohol, and then add salt (granular) to reduce the CO2. I did not have an excessive lye reaction with the flat beer (in fact very subdued reaction – but I had also had the beer in the freezer prior), but wondered about any residual CO2 in the beer – plus NaCl – how that reaction with the NaOH goes…
    I know CO2 affects acid/base levels in the human body!
    I even clicked on the link and bought the Scientific Soapmaking book, so maybe some answers there : )
    Many thanks,

  31. Very informative piece – thank you so much!

    Quick question: there’s a liquid hand washing soap my wife bought, it’s printed pH 5.5, and when I checked the ingredients, citric acid was in there. I am just wondering why would it be necessary to have such a pH value for a hand washing product. I mean, couldn’t it have properly worked had the pH been 9?

    I’d love to hear your expert opinion and any other experienced view(s) from the community. Thanks.

    1. Abdulmajid,
      I suspect what your wife picked up was technically a mild detergent rather than a true soap. Liquid soap generally falls in 8 to 10 on the pH scale. Trying to reduce it below 7 will likely cause cloudiness and separation.

      The 5.5 value is largely a marketing tool. Many companies use language like “pH balanced” to encourage people to choose their cleanser over true soap, since non-soap cleansers can achieve a pH closer to the acid mantle. However, as mentioned in the article, healthy skin quickly re-balances after washing with soap. So, yes, a cleanser with a pH of 9 would work properly; it would just lose the label appeal.

      You might enjoy this article as well: https://realizebeauty.wordpress.com/2016/08/30/can-you-lower-the-ph-of-castile-soap/

      Hope that helps!

  32. The tongue testing technique initially gave me jitters, but then i was relieved to see that you actually discouraged this method. A good pH meter, as you said gives accurate results, provided that it gets calibrated on a regular basis. The article is a blessing for those DIY soap makers out there who make good products but are wary to use them.

  33. Thank you so much for the information. I think I will go with the meter. Was never too keen on licking soap – esp. after looking at my gloves, and goggles. I have more respect for my tongue than that. 🙂 Just found your site after 12 years of making soap for family and friends, but I will be back … frequently, I believe!

  34. This is a great article! I am an industrial process chemist out of big pharma, and the work that Kenna has published would stand up just fine against of any lab work done by my previous groups. Dissolving a fixed amount of soap in a standard volume of water is great technique.

    The zap test. Instructing someone to test something with their tongue, that is known not to be a food additive or flavoring agent, would be a criminal act under OSHA today (really), so I am a bit annoyed when people suggest this test. Take Kenna’s advice, and don’t do it. However, some historical perspective is appropriate; this is exactly how things were discovered in the past when no other tests were available. The reason we know that certain compounds which were made in a lab or workshop taste sweet (or sour, or bad, or “zappy”, etc.) is because somebody, somewhere, at some point in time, tasted them. And, quite literally, they survived to tell others about it. But that doesn’t mean we have to keep repeating history – use the right tool for the job; buy some pH strips or a pH meter.

    I personally have not had any issue using the pH strips – either paper or plastic (I also use them to check the pH of my wort when I brew). Maybe that is just the result of several decades in a lab. But the pH meter is probably the best way to go. BTW, the only reason I check the pH is for safety – I want to know that there is not a large (or even small) amount of free, unreacted lye in my batch before I rub it on my skin.

    1. Hey, David,
      Thanks for the feedback! And yes, I’m betting your years of knowledge help you to get better results with the strips than the average soapmaker…the operator making the most of the tools so to speak.

  35. Thank you for the article. I had purchase lye that is in flakes not the normal beads and it has produced dry, crumbly soap. It is very toxic in comparison. When I left a review of the product on the website where I had purchased the product I was asked if I had tested the pH of the soap. I had not so I thought I would try not really understanding what the pH of my soap had to do with how my soap turned out when using this lye…but… I am so glad I found your article before wasting my time and money! My take away is pH is not static and therefore not very important. I just need to purchase my normal lye and all will be well again. 🙂

    1. Lynne,
      Are you measuring your lye by weight or volume? If you were purchasing the correct lye type to make bar soap and measuring by weight, the form shouldn’t matter.

  36. This article actually kind of proved that the tongue zap test is great, and does what it is supposed to, which is test for extra lye. Keep in mind that most people who use the zap test are simply using it as an extra safety step before sharing their soap with family or customers.
    The first step is measuring accurately so there is no danger if this is step one. Of course you don’t sell the sample that you test so that’s not an issue.
    PH strips look like a waste of money.
    And finally, the most experienced and successful soapmakers use a combination of methods to verify that their soap is safe, with the tongue zap test being number one!!

    1. As mentioned in the article, we do not recommend tongue testing:
      -If a new soapmaker unfamiliar with the appearance of lye heavy soap uses tongue testing, it could result in serious injury.
      -If you are a soapmaker in business, tongue testing is a liability, safety, and GMP (good manufacturing practices) nightmare.

  37. Hellooo,
    I’m in high school and doing an experiment to measure the pH of different soap and shampoo products…I’ve decided to use the red cabbage indicator to conduct my investigation. My science teacher supported this, but after reading this article I’m a little bit concerned…is the red cabbage test unreliable and used for child-friendly experiments? Or can it be used for a Year 10 Science Project? I would love your feedback and any other ideas that you could offer.
    Thank you!
    PS: This was an excellent read…even though I’m not in the soap-making industry 🙂

    1. Hi Sasha!

      I’ve used red cabbage indicators for homeschooling my kids and was first introduced to the concept in high school chemistry class, so I don’t think it’s too simplistic for you! Plus, red cabbage is readily available and affordable, so it’s a definite upside. Red cabbage will work similarly to the Universal pH Indicator I used for this article, showcasing a variety of colors based on the pH.

      A lot of soaps and shampoos that are commercially available are made with detergents, which are more soluble than true soap is. I’m not sure if you’ve delved into colloids yet (I believe I was first introduced to them in college!), but that is why pH testing soap can be difficult or unreliable. pH testing is meant for actual solutions. I touched on this concept lightly in the end of the article, but for a more in-depth discussion, check this article from a college course text: https://chem.libretexts.org/LibreTexts/Heartland_Community_College/HCC%3A_Chem_161/12%3A_Solutions/12.7%3A_Colloids

      I hope that helps, I think you are heading in a great direction!


  38. Thank you very much for a practical and accurate post. I have tried some of the methods that you described as inaccurate and I was never satisfaced. Thank you again. Besitos 😚 from the south of Spain

  39. As a new soap maker, I find there is so much misinformation on the internet from soapmakers who don’t know enough about the chemistry of their hobby/business. So THANK YOU for this article! It made things a lot clearer, and answered my questions that were arising in reaction to others’ clearly flawed testing methods.

  40. Thank you so much Kenna for all the information shared here in your blog. I’ve been reading it for a couple of months and learning a lot.

  41. Hi there. Rose Ingersoll in her comment of June 2017 asked a question that I’d love to hear comment on: “My question is, if my soap is not lye heavy, how long does CP soap really have to cure? The standard seems to be 4-6 weeks but why? How do I know if it’s ready to sell at 3, 4, or 6 weeks? Is that curing period related to the ph or lye “content” or some other factor. Soft oil sops obviously need longer to cure purely for the quality of the bar. But hard oil soaps? What is the bottom line?”


    1. Hey, Kate,
      It varies. 🙂 We go into intense detail about formulation and how it influences the speed with which soap batter saponifies and cures in our formulation workshop: https://thenovastudio.com/product/video-eclass-formulating-soap-recipes/.

      Cure time allows the soap to both fully saponify and lose water. For production, Kenna shoots for about a two week cure time for her soaps. But she formulates and provides a curing environment that supports that. Not all soaps would be ready in that time.

  42. Thank you toooooo much kenna.
    I am a new soapmaker and every time I have a query on something I found you answer it.
    you are very hardworking person I wish you more success.

  43. A first for me. Tried hot process soap for the first time. The recipe’s author recommended the zap test. Well, I did it. And I will never do it again. Wish I had found your information first.

  44. You are using the Apera PH20 in this article. I did some quick looking and I found that Apera makes another pocket pH testing device called the PH60S which is designed for testing “soft solids” such as: “cheese, fruit, sushi rice, and soil”. It is considerably more expensive than the PH20, but I wonder if this tool wouldn’t make the testing of soaps much easier. Especially hot process soap, before it’s put into the mold. What are your thoughts?

  45. Wonderful! I’ve been a soap hobby-ist for almost 20 years and have just now started wondering about ph since more people are interested in my creations. One person told me “it irritates” certain areas of their body, so I started to wonder if my ph was off…though I’ve never had anyone else make that comment. I did buy some ph strips, but wasn’t sure the proper way to test, or if the tests really mattered. Your explanation is so good, I’m book-marking it for future use when I’ll probably need to explain things to my friends and family 🙂

  46. Hi! Just to make sure, if my liquid pH is around 8.5 ( I use pH meter) is it safe to use? But when I dilute it ( around tea spoon on half glass of distilled water ) it is super cloudy. I cooked it about 2 hours only. Should I cook it longer? And test the pH again? What if the extra oil makes the soap cloudy? Can we do something to make it clear. I think I go overboard on superfatting ( around 10%). Thanks

  47. Hey there,
    I just ran across your article with regards to the PH test review and wanted to thank you for your effort. The information was very helpful and easy to comprehend coupled with a light-hearted style I was totally hooked ;-).
    I’m new to your site so and am a (proficient rookie ;-)… where soap making is concerned….
    I’ve made a couple of batches where my friends at work asked for some bars which was a ego boost 😉
    Now for some info wrangling — I’m a guy and my tendency is to run a recipe more towards simplicity not too many fragrances….
    Just tried my hand at recipe with Vetiver, Bergamot, and Cleary Sage as well as some others… but could you point me in a direction that can help me with a basic foundation of scent mixing.
    The whole base-note with secondary and tertiary notes really didn’t make that much sense to me. In the few articles I did read I wasn’t given a clear idea as to how the (3 note chord construct) interacted with each note and what the end game was supposed to smell like ;-(…..
    I know this is a subjective area (scent) and I think I went kind of spare with my above recipe; and am please to say that my last batch I pleased with the outcome but I think it was just pure luck….
    and the price of Vetiver was an eye-opener so I kind of would like to hedge my bet…
    any advice would be greatly appreciated…

    1. Hi pj! Welcome to the tribe! Soapmaking sure becomes addictive quickly, doesn’t it? 🙂 The topic of blending essential oils (and fragrances) is quite the extensive one! If you’ve already read all the articles I’ve written here, I would suggest picking up a copy of the book I wrote on the topic to get more in-depth: https://www.modernsoapmaking.com/product/smellgoods-book/

      We also created an extensive database of essential oil blends called the EO Calc. A lot of folks find it easier to learn how to blend essential oils by using blends created by others to get a feel for what they like and don’t like. Here’s the link to the calc: http://www.eocalc.com

      I hope that helps!

  48. Hello – I’ve been a fan of your page for ages now. I have a quick question. Can I use the water from my dehimidifier as distilled water for my cold process soap?

  49. Hi there

    I need your help please.I am making hand crafted bar soaps.1kg mixture content.How many drops of lavender essential oil can I add?

    Your fee will be highly appreciated.

  50. For a looong time I have not found such an informative site. You are wonderful. Keep up. Reading you from Nairobi, kenya

  51. Pingback: How To PH Balance Soap & Test The Level
  52. Amazing and very useful research! I have some other concerns about soap. Most of the soapmakers state that they are making 100% natural soaps, which I think it’s impossible because the saponification process is chemistry, after all. They try to support their claims with the statement that in the final product there is no NaOH, which in my opinion it is not possible. If the product is alcaline, which it is, it is a result of the salts in the soap. I would really love to see your aproach to this. Thanks!

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