Thursday, December 11, 2014

pH Testing Your Soap

I think I'm going to cut to the chase on this one.  I'm horrible at keeping up with this, and it's been on my mind to finish for a long while.  Having this finished will also allow me to simply copy it's link to provide in online forums and Facebook groups, rather than having to repeat all this info. 

I've seen an insurgence of folks wanting to learn how to pH test their soaps.  While many are still inclined to use Zap Testing to test for "doneness",  I prefer a more scientific, and frankly accurate, approach. What is zap testing and why to I feel it isn't as accurate as other methods?  Before I continue, I want to say I don't mean to offend, (typically I don't care if I offend anyone or not).  But just to be clear, that is not my intent.  I'm simply presenting my case.  Now, zap testing is essentially licking, or tasting you soap to see, or feel, if the soap has fully saponified.  Meaning no free lye is present.  I feel it is inaccurate because of the varying responses that are given to describe what it is actually like to zap test.  Many people will compare it to licking a 9V battery, with the assumption that everyone has done this in their childhood.  I haven't.  So I wouldn't know what that sensation is like.  Some say it just tastes nasty. But, doesn't soap taste nasty to begin with? Isn't that nasty taste why Moms of old used it to wash the mouths out of potty mouthed children?  I remember getting soap in my mouth during bath time.  It's not pleasant, and I asume that since it's commercially made, there is no free lye present.  Whether it was a liquid wash, or a green bar of Ivory.   In any case, the feeling is different for everyone.  Even more perplexing, some don't "feel" anything at all.  Meaning they don't get zapped.  Most soapers would equate that to the soap being OK to use.  However, I've personally zap tested a soap paste that had a lye excess, 'cause I'm weird like that.  And  I was fine.  No shocking feeling like a 9V battery.  No sting.  Nothing.  Just..soap.  And then, I've had the misfortune of reading a thread on Facebook where a young lady actually zap tested her soap batter before pouring it into a mold.  Soap batter is not quite soap.  It's the emulsification of the lye fluid (water, milk, beer) and the oils used. But it isn't fully saponified soap.  All comedy aside, this is a testament as to why I feel zap testing is inaccurate.  To me, accuracy is a practice that is constant that has predictable results across the board. In zap testing, there is no constant.  Not only is each individual different in how something will taste and feel,  but each recipe is different, down the the actual SAP numbers of the oils used (meaning the SAP numbers presented on your favorite soap calculator, may not be the same as what the actual oil's SAP number is.  In the end, you must KNOW what a soap with free lye truly tastes like, which is indicated on page 76 in the book, "Scientific Soapmaking", by Dr. Kevin Dunn. In that section, he describes how you can go about zap testing, and what he speculates you should feel when you do so.  However, in his book, he indicates that zap testing is used for indicating alkalinity, or alkali, not free lye.  I do not know if they are one and the same in this case.  For the purpose of this blog, I'll assume so, since soap makers understand free lye, not alkalinity.  Also, you must test several sections of the soap.  One side may zap, but another not.
I also feel it can be dangerous.  What if the soap still has free lye?  What if you're actually able to get a sensation?  You would essentially be subjecting yourself to a chemical burn, should the zap test fail.

We all know that handcrafted soap has a pH around 9-ish on average, for a well rounded, superfatted recipe.  Some folks will say between 9 and 10 is good. Dr. Dunn indicates that soap is "tongue neutral" (no zap) in a range between 8-10.  I err on the side of caution and say around 9, as the higher the pH the more likely you will have free lye. Essentially, just stay below 10. And the lower the pH, the more likely you could have issues with the soap hardening. Though I will admit, some soaps, such a Castile (olive oil soap) will garner a natural pH of 10-10.2.  I discovered this on a Castile batch with a 0-1% superfat. Most soap makers superfat at 5% and above.  Superfatting actually lowers pH a little, due to the excess fatty acids present in the soap.  Higher the superfat, lower the pH. So technically, you shouldn't get zapped if you're superfatting, as the free fats will consume all of the available lye in a fully saponified soap.

Why am I concerned with pH? Well aside from the free lye issue, I also like to acidify my soap, meaning i purposely lower the pH in my soap, to attain a milder soap. You can find out more about this on my post, here, here, and hereEssentially, skin prefers acidic cleansers, as they are less likely to harshly strip away the acid mantel of the skin, the way alkaline cleansers do. Also, the acid mantel recovers much faster the less alkaline a cleanser is, as determined by this study using 48 volunteers in Sri Lanka.  And the same is for hair care as well, in that when in an alkaline environment, the cuticle of the hair shaft 'lifts' or 'opens'.  Some folks would think that is good, to allow more nutrients in, but it's not.  The shaft opening in such a way is quite damaging, since the cuticle isn't meant to do that.  It's even worse for folks who do the vinegar rinse after, as the acid closes the shaft, thus causing more damage to the cuticle.  It's not a door.  It's not meant to open and close that way.  This is why hair care products are acidic. To keep the cuticle closed.  Also, a closed cuticle will allow more light to reflect off it the hair, because it's smoothed.  Thus the "shinier hair" claims of most products. The alkaline environment also strips the hair of it's natural oils, with superfatting replacing them.  It does the same thing to skin as well.   Here are some links to support my stance on using alkaline products in the hair.

Anyways, enough hard science for the day.   Whatever your reason for testing pH, you need to be able to test it properly, so that you attain consistent, accurate results every time. Next, I will provide you will a few different methods for testing pH.  It's essentially up to you to decide which will work best for your purposes.

When testing pH of soap, it needs to be in solution, either a 1% or 5%, regardless of method.  Either will do.    For a 5%, dissolve 5 grams(g) of soap in 95g of water.   Or for the 1%,  1g in 99g. 
When testing bar soap, make sure you take your sample from the INSIDE of your soap.  Truth be told, the outside is slightly less alkaline than the inside, due to air exposure. When testing liquid soap, the most important test time is the finished diluted soap, since that is what will be used in the bath.  However, testing during the cook phase for the soap paste tells you when you can stop cooking and move on the to the next phase.

pH Meter
The most accurate testing method is a good pH meter.  Preferably one with automatic temperature compensation, and can be automatically calibrated (single button calibration)  rather than manually (using a screw driver in back) to avoid user error.  But that feature depends on cost to the user. The meter I use is the Hanna HI 98129.  And make sure you purchase the appropriate calibration and storage fluids, to ensure accuracy and proper care of your meter.  I chose this particular meter to also test the Total Dissolved Solids in our drinking water, since we use a water purifying system that needs filter change based on that reading.  Also, keep in mind, that cheaper meters tend to not last very long. You may get anywhere from 6 months to a year out of one. Especially with those that do not have an interchangeable pH probe (the part that tests the pH).  If you can change the probe, you'll get more life out of your meter. I can't give advice on whether the cheap garden meters are OK to use.  They may have a limited pH range, or may not be able to withstand the alkalinity of soap.  The uncertainty is why I opted for a pricier meter.
Phenolphthalein (phenol-p, phph)  solution drops. You will need the kind that go from clear to pink NOT red.  Red is for pools, and test a different alkaline range.   The drops we will need will react to alkaline solutions within a certain range, between a pH of 8.2 to 10.  Some sources have said 12, but they are VERY few), by changing from clear to pink.   All my tests have shown up to 10, when compared to my meter  The color range is your indicator, from faint pink(low end)   to bright fuschia(almost reddish)(high end).  So when you place your drops in solution, use a white background to help determine the coloring.  You want faint pink.  On the flip side, if your drops read perfectly clear, most folks will say that is perfect and therefore the test sample is not lye heavy. That is false. Soap cannot naturally be a pH of 8.  Ever.  Only when you purposely lower pH can it go that low, and lower even.  Otherwise, soap will remain above 8.  So if your solution is clear, your soap is lye heavy.  I will direct you to this thread in in Chemical Forums for more detailed explanation, especially on why we don't test directly on the soap.

Test Strips/Papers
If drops seem too confusing, the use of lab grade pH strips is recommended.  You get what you pay for when going cheap on strips, and that includes an inaccuracy of up to 2 points. Here is a link for more info, plus recommendations on strips to find.

And here is more infoor ideas on testing soap.  I'm not too fond of them, but it is a different perspective other than my own.

Regardless of what method you choose, you are to do your best to ensure that you are performing it correctly.  A test is useless if you don't follow some sort of structure with it to ensure consistent results.  So, until next time.  Good luck!