re-visiting the PH meter issue

I haven't made soap or been on the forum for a very long time.
My daughter asked me to make some soap for her and the new grand baby, so did a bit of calculating and made some colostrum soap which seems to have turned out fine. However, in the past I have made different mistakes in measuring , either in a hurry or what ever, so when dealing with making soap I want to find a PH meter that is for soap making. there are a number of PH meters for gardening, but the makers say they won't work for soap. Anyone out there know of a reasonably priced PH meter that has a metal probe on it and will work for soap making?
would love to hear your thoughts..
Thanks..

Meters are pretty cheap. Probes (good ones) are at least a couple hundred dollars, and you will also need some calibration buffers if you want good results. I'm floored every time I have to buy another one at work.

There is no cheap solution, I'm afraid.

Here's a link to a good article about testing pH.

http://www.modernsoapmaking.com/how-to-ph-test-handmade-soap/

PH testing is rather useless in soapmaking. You are much better served to just do a zap test. You can have a reasonable PH reading but it won't tell you if you have active lye. You asked this same question in another thread as well.

"...I have made different mistakes in measuring , either in a hurry or what ever, so when dealing with making soap I want to find a PH meter that is for soap making..."

If you are making mistakes often enough to not be confident about the accuracy of your soaping, maybe a better approach would be to look at creating good work habits to minimize the chance of mistakes. What errors do you tend to make? If you would explain, then perhaps we can make suggestions about working smarter.

I use the zap test to check my soaps, but more because I like to check for my own personal education than I am worried the soap is lye heavy or whatever. I'm really confident that how I work when I make soap will result in a safe, good product.

Having used decent pH meters in the past, they're a pain if take the time to care for them properly. If you don't use the meter regularly, it can end up being more trouble than it's worth. And like the others are pointing out, the pH of a particular soap doesn't necessarily tell you if there is excess alkali in the soap or if the soap is fine.

shunt2011 said:

PH testing is rather useless in soapmaking. .... You can have a reasonable PH reading but it won't tell you if you have active lye.

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I couldn't agree more. I use phenolphthalein to check for active lye in LS. But it should be said that this is a point of confusion for newbies.

DeeAnna said:

I use the zap test to check my soaps, but more because I like to check for my own personal education than I am worried the soap is lye heavy or whatever.

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This just me. I'm not a scientist; I just know what works for me and I don't like the zap test at all! With apologies to all who might be offended, I think it's dumb and would not recommend it, but I do understand why you would use it for education purposes, DeeAnna.

As Kenna says in the link above:

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.

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!

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That's pretty much where I stand on the Zap Test. I fear I'm stepping on toes here, but I hope we can all agree, based on my years of experience, I'm entitled to my opinion. As Shari said, pH testing soap isn't necessary. Neither is zap testing necessary, to my mind at least, for the reasons stated above.

That being said, I once had a pH meter to test the pH of soil in house plants. It was double-pronged and useful early on in making liquid soap -- the prongs were long and reached a good distance into the pot. Accurate or not, it did give me a feel for where the diluted soap ended up. I could then add 20% citric acid solution to adjust the pH down a bit until it registered pH 8.5. That gave me a "marker" for future batches. Whether accurate or not, didn't matter. It gave me peace of mind to know that it had dropped from where it was, did not separate, and stayed there with later testing.

Nite Hawk said:

Anyone out there know of a reasonably priced PH meter that has a metal probe on it and will work for soap making?

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LOL I forgot to answer your original question! Taking all that has been said into consideration, Kenna's recommendation is this one:

http://tinyurl.com/yc55my2w

Apera Instruments AI209 PH20 Value Waterproof pH Pocket Tester, ±0.1 pH Accuracy, 0-14.0 pH Range, Complete Kit - $49.50 plus FREE shipping.

I do not live in a perfect world, I live in a large very active household, and even though members are told not to bother me when I am doing certain chores, things do come up that require my attention, and therefore interrupt my concentration.
I have done the "zap" test but figure there should be a better way, and the idea of licking lots of soap is not my idea of a good time!! LOL
I find litmus paper- difficult sometimes to decipher the color completely correctly, that is why I am "picking people's heads" about PH meters again, seeing if there is anything new out there since the last time I was involved with soap making, which has been quite a while.
New innovations and ideas occur and was looking to see if there was any new input....
Thanks!

Zany_in_CO said:

With apologies to all who might be offended, I think it's dumb and would not recommend it, but I do understand why you would use it for education purposes, DeeAnna.

As Kenna says in the link above:

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I love Kenna, but I completely disagree with her stance on the zap test. Dr. Kevin Dunn (based on his several years of experience up his sleeve as a scientist/chemist) gives a defense of the tongue test (aka zap test) complete with directions on how to properly conduct one on page 76 of his book Scientific Soapmaking, which we made into a sticky here. Based on his experience as well as my own 11 years of soap-making experience and conducting the zap test properly, I do not consider it to be 'dumb', nor do I consider it to be dangerous if properly conducted.


IrishLass

IrishLass said:

Dr. Kevin Dunn (based on his several years of experience up his sleeve as a scientist/chemist) gives a defense of the tongue test (aka zap test) complete with directions on how to properly conduct one on page 76 of his book Scientific Soapmaking, which we made into a sticky here.

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IrishLass said:

Very carefully touch the lather on your finger to only the very tip of your tongue

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As I said before when this subject came up, with all due respect to Kevin Dunn, it's better to touch the side of your tongue rather than the most sensitive taste buds on the tip of the tongue... save that for licking ice cream, among other things. :mrgreen:

Just because I think it's dumb doesn't mean I think you're dumb, Irish! LOL Quite to the contrary, I think you're brilliant, kind and generous. I hope you and others don't take it personally. It's a matter of opinion based on our own knowledge and experience. And we all know that opinions can, by their very nature, be neither right nor wrong. With the safety of newbies as our focus, they deserve the benefit of both sides of the issue. Yes? For their sake, I hope we can agree to disagree on the subject.

Isn't general advice to wet a gloved finger, then rub it against the soap, then gently touch the tip of the glove to the tip of your tongue?

There's nothing unhygienic about that.

As far as safety is concerned... I'd rather give the tip of my tongue a tiny little zap than use lye-heavy soap for weeks and damage my skin, or gift the soap to a friend and have them get hurt by it.

toxikon said:

Isn't general advice to wet a gloved finger, then rub it against the soap, then gently touch the tip of the glove to the tip of your tongue?

There's nothing unhygienic about that.

As far as safety is concerned... I'd rather give the tip of my tongue a tiny little zap than use lye-heavy soap for weeks and damage my skin, or gift the soap to a friend and have them get hurt by it.

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All of this. I'm still new enough at making soap that I'm not entirely confident that all of my batches are going to turn out (and I'm right to be so cautious- had a batch recently partially separate in the mold, which I didn't even realize... until I tested it and parts of the bars were lye heavy). Be damned if I'm going to use, or worse give someone else to use, a bar of soap that I'm not certain is safe to use. Ph testing will not tell me if that bar is safe. Zap testing will. Seems a pretty cut and dried decision to me.

"...I do understand why you would use it for education purposes, DeeAnna..."

Gee. I feel honored that you would take the time to express your understanding of my doing something you think is so dumb. Thanks. :think:

***

For the record, I do Not Lick my Soap, and I find it annoying that the naysayers and never-do-ers are so quick to say this is how a zap test is done. I've worked pretty hard at trying to educate people about doing the zap test safely, as has Irish Lass and others.

If a person doesn't zap test, then fine -- just say you don't zap test and be done with it -- don't perpetuate a myth of "licking soap" that exposes newbies to unnecessary risk. It's like saying you dislike guns, but decide to give a toddler a loaded gun, and when they get hurt, then using that as further justification for your dislike.

Licking one's soap has two major issues over doing the zap test the way that IL, Toxicon, others, and I do. It disqualifies a perfectly good bar from being giftable or salable. It also exposes one's tongue to unnecessary risk, should there be an unusual problem with the soap. All that's necessary is a light rub on the bar with a clean fingertip and a tiny touch to the tongue. Immediate rinse the mouth and spit if there is any undue unpleasantness going on. Minimal risk. Optimal results.

I doubt this will change anyone's mind, however, so let's agree to disagree and move on.

pH meters have no possible way to detect free lye in soap. None. It does not matter what the pH is, it matters whether there is free lye or not. Zap testing tells you if there is free lye or not.

Phenolphthalein is an easily mistake prone method of determining pH. NOT the presence of free lye.

Calling perfectly scientific methods of determining the safety of soap dumb just because you disagree with it is rather immature IMHO.

And a condescending tone will alienate lots of folks. Just sayin'.

WHOA!
I sure never meant for this to be a free for all!
First I have a question-quote--"a Ph meter will not detect free lye"--Now why won't it? if lye is PH 14 and there is a liquid lye floating, why won't it detect it??
Also due to an experience I had the other day, I totally believe the zap test is unreliable.
Laugh if you will, I stuck my tongue on the new bar of soap that I had made about a week and a half ago- and it was totally fine. I had washed with some of the crumbles and actually had gotten some in my eyes and other than tiny bit of discomfort it was fine.
However, when I broke the bar of soap in half that I had just touched my tongue to, and touched my tongue to the inner portion, it was still a bit "hot"!!!
The outer surface was fine, the inner part that was broken in half was definitely not ready yet.
So I approach that the zap test may tell what the surface of a bar is, but not what is happening on the inside, Therefore I am wondering if a PH meter with a probe might tell what is happening on the inside..
There ! I just threw fuel on the debate, however I am serious, My daughter wants a soap for the grandbaby, and I sure don't want to burn her, that is why I am asking this question!

There are a couple problems with using pH to tell if your soap is ready.

You've touched on one -- the outer surface and the middle of the bar can be different.

However, the real problem is that pH will not measure residual lye, nor the state of cure in soap.

pH is the measure, using either color changing dyes or an electrode sensitive to hydrogen ions, of the hydrogen ion concentration in water (actually, the negative logarithm of the hydrogen ion concentration). This is fine as far as it goes -- sodium hydroxide solution is much much higher pH than finished soap BUT what is important is not the hydrogen ion concentration but the AMOUNT of lye (hydroxide) left in the soap.

You can use a pH meter to determine the amount of lye, but to do so you don't just read the number, you must dissolve the soap and then add measured amounts of a known acid to neutralized the lye. This is called titration, and the pH number will only tell you when you have neutralized the lye, not how much there is.

Also, to get the actual pH of the soap, you must completely dissolve a known amount in a known volume of water (I don't know what that weight or volume is, but you can find out). You then measure the pH of the solution formed, not the surface of the soap. This fixes the first problem. It still won't fix the alkalinity measurement issue, you still have to titrate to get that information.

pH probes all have what is called "sodium error" -- the special glass that is sensitive to hydrogen ions is also slightly sensitive to other small cations (sodium, potassium. etc) and in the presence of high levels of sodium, will read lower pH that they are supposed to. We have this problem at work, as we have large amounts of caustic (sodium hydroxide solutions) in our various processes, and have to be careful about high pH numbers. Strong caustic reads much lower than it should. A 1 Normal solution of sodium hydroxide should read about pH 14, and usually shows on my meters as 12.5 to 13. Soap has quite a bit of sodium in it, and hence you can get errors due to sodium sensitivity at the electrode surface, particularly if you don't have a low sodium error electrode.

And finally, cure isn't something you can measure with pH -- it's really a crystallization/water loss/solubility change, during which the pH will change but not in a way that you can measure and decide from that pH value if the soap is ready.

By all means, get a pH meter if you want, but it's probably cheaper and just as useful to get some wide range pH paper or test strips (we use Merk ones, made of plastic at work, but they are not inexpensive). Paper or wide range strips will give you the same information without the hassle of maintaining and calibrating a pH meter.

You should also understand that the "zap test" is a measure of lye amount (alkalinity) rather than a pH test. Your tongue responds to the amount of lye with the "zap" response -- high pH solutions are just very bitter as a rule, unless they have large amounts of akalinity.

"...Now why won't it? if lye is PH 14 and there is a liquid lye floating, why won't it detect it??..."

If soap has lye floating on it, then there's a problem with how the soap was made. A person doesn't need to know the pH to figure that out.

"... when I broke the bar of soap in half that I had just touched my tongue to, and touched my tongue to the inner portion, it was still a bit "hot"!..."

And the answer is ... don't DO that. Saponification takes time to fully complete, the reaction is not necessarily consistent throughout the soap, and variation in soap making methods also have an impact -- and this last point is especially true when a person is new to soap making and may not have the best technique yet.

You learned these lessons to your tongue's dismay, and I'm not laughing a bit at your experience ... I'm shaking my head at your lack of caution. If you don't have a reasonable certainty that the soap is skin safe, then be cautious. And even if I'm reasonably certain, I'm still test cautiously. A cautious zap test is sufficient to collect the information needed at minimal risk -- why do more?

***

You're assuming pH is an absolute measure of excess alkali and is a valid way to determine whether soap contains free alkali or not. A lot of people who do not work in the chemical field make this assumption. Despite what a lay person's "common sense" might suggest, this idea about pH is incorrect.

Any given blend of fatty acids will make a soap with a characteristic pH. A soap with pure oleic acid has a characteristic pH of about 11.2. A soap with pure lauric acid has a characteristic pH of about 10.1. A soap with a blend of fatty acids will have its own characteristic pH.

So ... you tell me ... if I have a properly made lauric soap with a pH of 11.2, does it have excess alkali? If I have an oleic soap with a pH of 11.2, does this soap have excess alkali? If I have a blend of fatty acids in my soap, is a pH of 11.2 a valid and safe pH for this particular soap?

***

And furthermore, let's assume I can measure the pH really accurately and I know from repeated tests that the pH of a given soap recipe should be, say, 11.0. I make a batch of soap using that recipe. If my determination of the soap's pH is 11.1, does that mean the soap is not skin safe? Or does it mean that the fats, which are natural products given to natural variation in their properties, might have changed slightly and the resulting pH of the soap has changed in response to that variation?

Why not just titrate for free alkalinity and KNOW whether the soap is skin safe or not? Or do a zap test and get essentially the same answer?

Again, the answer of "safe" vs "not safe" is NOT the pH of the soap. It is a test for free alkali, as Psfred explains above (and I have explained elsewhere, many times).

Maybe Psfred will explain the matter in a way that actually makes a difference.

***

Inexpensive pH strips are very reliable in that they reliably under-report the pH of soap.

Machery-Nagel and similar high quality pH strips work reasonably well in a dilute soap solution, but they aren't cheap.

Rubbing a pH test strip on a dampened bar of soap, as many soapers do, is not accurate, regardless of the pH strip one uses. Again, the pH reported by the strip is lower than the actual pH.

More:
http://www.modernsoapmaking.com/how-to-ph-test-handmade-soap/ I disagree with Kenna about the value of the zap test, but her info is otherwise good.
http://alaiynab.blogspot.com/2015/05/ph-testing-of-liquid-soap-and-lowering.html This is about liquid (KOH) soap, but the info also applies to bar (NaOH) soap

Let me try this analogy:

Imagine a 3" PVC pipe ten feet long set on end, full of water with a valve at the bottom, and a 5000 gallon tank ten feet high with a valve at the bottom.

The pressure at the valve will be exactly the same on both, but if you open both valves, you're gonna get a whole lot more water out of the 5000 gallon tank.....

pH is like the pressure at the valve, alkalinity is like the water in the container. Not an exact representaion, but close enough.

Fatty acid salts will buffer the pH lower even if there is plenty of free lye in the soap, but even at fairly low pH (say 12) the alkalinity of the free lye will overwhelm your skin's buffering capacity and result in irritation or burns. Fully cured soap at pH 12 won't, because your skin can buffer the pH down.

Hope that helps, it's difficult to explain this stuff unless you know some chemistry (and why chemistry is hard to learn for many people)

This is fascinating stuff. I love learning the hows and whys behind the whats of making soap.

If there's free alkali then it should zap your tongue. If there is no free alkali then it has either turned into a soap salt or sodium bicarbonate and will not zap your tongue. It really is that simple.

The other half of the "result" is that it only tests that particular area you tested, so it's not indicative of a bar of soap as a whole. You can have a lye pocket an inch away from fully formed soap and the soap won't have any free alkali, but the pocket will.

wetshavingproducts said:

If there's free alkali then it should zap your tongue. If there is no free alkali then it has either turned into a soap salt or sodium bicarbonate and will not zap your tongue. It really is that simple.

The other half of the "result" is that it only tests that particular area you tested, so it's not indicative of a bar of soap as a whole. You can have a lye pocket an inch away from fully formed soap and the soap won't have any free alkali, but the pocket will.

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And if this is the case (and I have seen it happen), then even a pH meter with a probe is still only going to test the pH of a particular spot where it touches. I am not defending pH meters, per se, because a specific pH does not equal lye, just pointing out that all tests are only going to give the results of the area tested. That's just the way it is regardless of what you test and how what method you use, be it soap or dirt or any other solid. It would of course be somewhat more reliable with liquid soap, I expect because it is already in solution and one would expect a fair uniformity of said solution.