Hello, I tried to dig, but didn’t find. The question is: is there any way to check if all oils in my KOH and NaOH soap are saponified? My target is 0% (zero) superfat as a first step in creating recipes for some detergents and I’m sure, that (for example) 90% pure KOH isn’t 90% in fact, but 89,5% or 89,3 or else.
Saponification check
- Thread starter Tomek1979
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Zap-test!
Give the soap at least a week to finish the saponification process, then wet a gloved finger with water, rub it on the soap, then gently touch your finger to your tongue. If you feel a little ZING like putting your tongue on a battery, that means there is still active lye in your soap.
Give the soap at least a week to finish the saponification process, then wet a gloved finger with water, rub it on the soap, then gently touch your finger to your tongue. If you feel a little ZING like putting your tongue on a battery, that means there is still active lye in your soap.
You would need to know the true purity of your KOH or NAOH. DeeAnna has a way to test it. Then you would need to configure your numbers correctly.
https://classicbells.com/soap/lyePurity.html
https://classicbells.com/soap/lyePurity.html
There will be no way of knowing if all the oils are saponified.
The Zap-test gives a positive response for excess alkalinity (as hydroxide), but this is not an indication of saponification completeness (from the point of view of the oils).
That is, a soap might be totally saponified in respect to the alkali, but not in respect to the oils (superfat).
Knowing the purity of your alkali is important in order to setup a stoichiometric ratio (1 triglyceride takes 3 alkali "molecules", in order to saponify). However, it is not the only factor.
FA Oil composition varies depending on crop, varietal, producer, season, and geographical location. The SAP values are only the best average guess. Which is why soapers are fine with a moderate % superfat.
Furthermore, some oils, especially if unrefined, or cold-pressed, contains a considerable amount of unsaponifiable matter, usually in the fraction of a %, that throws off the balance.
Additionally, Alkali (both NaOH and KOH) could be titrated, however, titration is thrown off by the fact that there is a considerable amount of time elapsed when preparing the lye for soaping, and the moment you will be using it. This allows the alkali solution to absorb CO2 from the air and carbonate. Rates for this can be extremely fast, up to a loss of 1% lye / per hour, assuming a constant supply of CO2 and stirring.
Ergo, making an absolute 0% SF soap is virtually impossible with CP or HP methods.
Now, a different story would be using the classic boiling method.
This avoids all the problems enounced before by working with excess lye.
In doing this, and by working at high temperatures, you ensure your saponification is complete. Then, usually by cooling down, or dilution, or salting out, the soap is separated from the spent hydroxide solution at the bottom, and once cold enough, the soap is skimmed off the top. Usually, 1 or 2 more cycles of boiling with salt water or fresh water are performed, to ensure no excess lye gets trapped in the final soap.
The Zap-test gives a positive response for excess alkalinity (as hydroxide), but this is not an indication of saponification completeness (from the point of view of the oils).
That is, a soap might be totally saponified in respect to the alkali, but not in respect to the oils (superfat).
Knowing the purity of your alkali is important in order to setup a stoichiometric ratio (1 triglyceride takes 3 alkali "molecules", in order to saponify). However, it is not the only factor.
FA Oil composition varies depending on crop, varietal, producer, season, and geographical location. The SAP values are only the best average guess. Which is why soapers are fine with a moderate % superfat.
Furthermore, some oils, especially if unrefined, or cold-pressed, contains a considerable amount of unsaponifiable matter, usually in the fraction of a %, that throws off the balance.
Additionally, Alkali (both NaOH and KOH) could be titrated, however, titration is thrown off by the fact that there is a considerable amount of time elapsed when preparing the lye for soaping, and the moment you will be using it. This allows the alkali solution to absorb CO2 from the air and carbonate. Rates for this can be extremely fast, up to a loss of 1% lye / per hour, assuming a constant supply of CO2 and stirring.
Ergo, making an absolute 0% SF soap is virtually impossible with CP or HP methods.
Now, a different story would be using the classic boiling method.
This avoids all the problems enounced before by working with excess lye.
In doing this, and by working at high temperatures, you ensure your saponification is complete. Then, usually by cooling down, or dilution, or salting out, the soap is separated from the spent hydroxide solution at the bottom, and once cold enough, the soap is skimmed off the top. Usually, 1 or 2 more cycles of boiling with salt water or fresh water are performed, to ensure no excess lye gets trapped in the final soap.
Thank You!
@Imosca thank You so much! A lot of knowledge in Your reply.
I was wondering if there is any simple test to check unsaponified fats in ready soap, but it looks - not.
Could anyone invent some kind of stripes (as pH testing stripes) for saponification/raw fats test, please?
I was wondering if there is any simple test to check unsaponified fats in ready soap, but it looks - not.
Could anyone invent some kind of stripes (as pH testing stripes) for saponification/raw fats test, please?
You're welcome!
I was wondering if there is any simple test to check unsaponified fats in ready soap, but it looks - not.
Could anyone invent some kind of stripes (as pH testing stripes) for saponification/raw fats test, please?
I can tell you for sure there are tests for unreacted / unsaponified triglycerides, but they can be messy, expensive, and more laborious than not.
The main problem in doing that is that, chemically, a triglyceride is really not that much different from the fatty part of a fatty acid, and the main problem is trying to separate those two, so you can identify one or the others.
From the top of my mind, one could try the very simple test for unsaponified oils that I tend to do when I HP soap. I take a sample the size of 1/4 teaspoon of soap mixture, chuck in in 100 mL of distilled water and stir to dissolve/disperse. If I see oil droplets floating on top, that means that there is still oil to saponify. Unfortunately, this test is not at all accurate, I believe it will fail below 1-3% of oils remaining. Mainly because you have soap, and water, and a little oil. Soap will make its dang job, and emulsify the oil in water.
I might try to suggest the following and maybe, over the weekend, I will experiment a little to see if it works. I am not sure if anyone else tried; so the veterans of the forum can intervene to correct me.
- The CMC of sodium oleate (critical micelle concentration - that is the concentration of surfactant required to form micelles, below that it just behaves as a solute, not an emulsifier), is 3 mM, which roughly corresponds to 0.9 g of sodium oleate in 1 L of pure water at 25C.
- The CMC of any sodium-carboxylate surfactant is increased in water / ethanol mixtures.
- We can safely assume that by taking 0.1 g of soap mixture and dissolving it in 100 mL of a 10% ethanol solution will guarantee to be below CMC.
- Any unsaponified oil will not be emulsified with water and will thus float on top.
I can see several pitfalls, listed here:
1) additives like sugars can lower CMC in soap. Salt might precipitate the alkali soap from the water (salting out)
2) Fragrances and EOs will make a false positive test.
3) Incomplete saponification actually means that we do not know what's going on. Oils are saponified in 3 stages, from triglycerides to diglycerides, to monoglycerides to glycerin and fatty acid soap.
The more fatty acid residues we remove from glycerin the more the remaining glyceride becomes hydrophilic, monoglycerides, in fact, are emulsifiers (you can use them in food and lotions, as emulsifiers, emulsion stabilizers, thickeners, see for example, glyceryl monostearate). This might throw off the test as well.
Any thought about this will be welcome!
Cheers,
L.
Cool post Imosca!
How did you come up with the 1% rate?
(I'm going to come back to this thread for the topic itself, but I am curious about this bit)
How did you come up with the 1% rate?
(I'm going to come back to this thread for the topic itself, but I am curious about this bit)
I roughly extrapolated from some papers I was browsing.
Unfortunately, there is no official data on the matter, but I can check better tonight when I am home.
Most papers report different conditions from the ones a regular soaper uses, stirring, bubbling of CO2, spray scrubbers, film scrubbers etc... So coming up with a real number is not easy.
One paper I found reports the following conditions:
T= 30C, stirring at 80 rpm, surface area of lye solution 20 cm2, initial concentration of NaOH 6.7 M (27% lye), pCO2 = 1atm.
The initial rate of absorption is 2.10 mL/(cm2 x min) per CO2, which would convert down to a mass transfer of 4.1 g of CO2 / (cm2 x min), or 0.093 mol CO2.
While this result is difficult to understand in regular terms, we could imagine a solution of 1L 27% lye (6.7M), in a container, in contact with 1 atm of CO2, through an opening of 1 cm2 (not big, eh), and stirred at 80 rpm.
The initial rate would say that all the lye will be consumed in 72 minutes, but we are not considering the fact the less lye there is, the slower is the process. Unfortunately, this involves more math than I can do at the moment, but it can give you an idea. That is, anyway, pretty darn fast!
Let's consider that soapers use concentrations comparable to that reported in the paper (27% and up) and our surface areas (usually a small pitcher) are far larger than the 1cm2 used in the example.
Also, we do not work in concentration of CO2 even approaching the ones reported in the paper. The current partial pressure of CO2 is 0.04 atm. Far lower! This figure is usually higher in a closed environment, like a house, or a workshop.
1% / hour seems a good figure to extrapolate, in open container, with occasional stirring, and regular concentration of CO2, but I might have been undershooting.
Cheers,
L
Thank you for answering in detail. I questioned it because I thought it might be faster
Now, to look at what you've written, thank you!
Now, to look at what you've written, thank you!
Actually, Dr Kevin Dunn has done testing of the superfatted oils as he talks about in this article: http://www.google.com/url?q=http://...zApQQFggSMAM&usg=AOvVaw3vhZGrdcTtdYSzMnDLbBxf@Imosca thank You so much! A lot of knowledge in Your reply.
I was wondering if there is any simple test to check unsaponified fats in ready soap, but it looks - not.
Could anyone invent some kind of stripes (as pH testing stripes) for saponification/raw fats test, please?
As far as simple for th layperson, probably not in my lifetime. But he is a chemistry professor who does loads of soapy research. For detailed chemistry of soapmaking, I highly recommend his book: https://www.goodreads.com/book/show/9108135-scientific-soapmaking
