glycerin calculation

It dawned on me that in trying to compare the approximate amount of glycerin found in Coconut and Palm Kernel oils, that I didn't know the correct way to look up this information.  I want to compare these figures to those of fatty acids I am using in their place.  In searching, I don't seem to find what I am seeking and I think I am not putting in the correct terminology.  If you understand what I am seeking I would greatly appreciate your help in searching for these answers on my own, online.  Thanks!
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  • PharmaPharma Member, Pharmacist
    Not sure if I do understand what you mean... Maybe: Saponification value (for NaOH) / (3 * molecular weight NaOH) * molecular weight glycerol = mg glycerin per gram oil.
  • 256.5/ 3x40 (40 - the molecular weight of NaOH) x 92.09 (92.09 - the molecular weight of Glycerol) =  X  mg per gram of Coconut Oil  ?

    I'm not sure of the math symbols you are using...

    I just want to know the typical percentage found in one part of coconut oil and one part of palm kernel oil.

    Thanks...
  • BelassiBelassi Member, PCF student
    20% or so.
    Cosmetic Brand Creation. Concept to name to IMPI search to logo and brand registration. In-house graphic design inc. Pantone specs. Cosmetic label and box design & graphics.
  • Belassi, good to hear from you!  WOW!  That sounds like an awful lot of glycerin for either coconut oil or palm kernel oil to possess but it certainly would make a difference when one replaced coconut oil or palm kernel oil with Coconut Fatty Acids, or Lauric or Myristic Acid!  Something to consider...  Thanks!
  • PharmaPharma Member, Pharmacist
    These 20% are what you get when actually calculating my proposed formula ;) . Depending on the quality of coconut oil, you may subtract 5-10% from those 20% depending on the amount of free fatty acids.
  • BelassiBelassi Member, PCF student
    This is why I no longer make cold process soap (or hot process either). The amount of glycerin in the bars makes them sweat whenever the ambient temperature + humidity gets past a certain point. I assume that what's happening is that the glycerine in the soap absorbs water vapour, then begins to leach out.
    Cosmetic Brand Creation. Concept to name to IMPI search to logo and brand registration. In-house graphic design inc. Pantone specs. Cosmetic label and box design & graphics.
  • Thanks Pharma and Belassi!  I've been aware of the difference in using fatty acids and oils in regards to the glycerin content but never attempted to try and calculate it to find out the actual percentages of glycerin in the oils being used in some of the sample formulations.  In retrospect, I should have done it years ago!  I'll be able to compare sample formulations in a different light now! 

    Belassi, having been a soapmaker for 20 years, I understand what you are saying but have encountered very little of what you are saying in my work but sometimes a fragrance can do the same thing. (but my products have also been kept in air-conditioned places over the years!)  "Green Tea" was one that proved to be difficult with some versions "sweating" seasonally and other versions "sweating" on a regular basis!  Now I understand why the process of "salting out" during some soapmaking (tons of info in old soapmaking books) occurs!  You would think that soapmaking would be a simple concept with simple procedures whether it is handcrafted soaps, shaving soaps or shaving cream (which is what this question is referring to)!  Thank you both for your assistance.  It helped explain this aspect of formulation and proved that my trip down this pathway was the right move to make!  YAY!!!!!!!!
  • Pharma said:
    These 20% are what you get when actually calculating my proposed formula ;) . Depending on the quality of coconut oil, you may subtract 5-10% from those 20% depending on the amount of free fatty acids.

    Pharma, You didn't indicate whether I had gotten your "proposed formula" right but I'll go with it:

    256.5/120 X 92.09/1 = 23.621/120  then if I divide and 23.621 by 120, I come up with 0.196.8/1  Is that correct? 

    Or do I take the 23.621/120 ~ x/100 = 19.68 which would be right in the 20% range!  That make more sense to me but I still want to know if it is correct!
  • PharmaPharma Member, Pharmacist
    Wait, what? Why so complicated! The first part is all you need:
    256.5/120x92.09 type that in a calculator and get 196.8 or more precisely (for 1 gram of oil) 256.5 mg/120g/mol*92.09g/mol=196.8 mg glycerin per gram oil. Because mg/g equals per mill, if you divide again by 10 you'll get percentage: 19.68%.
    To saponify coconut oil one requires 256.5g NaOH or 3 molecules NaOH per molecule triglyceride to end up with 1 molecule of glycerol (and 3 molecules of soap). That formula simply "transforms" the weight of 3 parts NaOH to 1 part glycerol by using their respective molecular weights (that's the g/mol which crosses itself out in the equation).
    You could as well go with a "weightless" formula directly based on %: 256.5mg NaOH per gram coconut oil = 25.65% NaOH no matter how much oil you take divided by 120 and multiplied by 92.09 equals directly % glycerol. If your saponification value is based on KOH, simply use 3 times the molecular weight of KOH for the division instead.
  • First, I am working in ounces not grams (which really doesn't matter). I was describing two different options of your original formula, as I saw them and the second one seems to work the best like this:

    256.5/120 X 92.09/1 = 23.621/120 ~ x/100 = 19.68%

    I don't see this as complicated at all.  It easily gives me the approximate amount of glycerin in one part of Coconut Oil which is what I am seeking.  You do the first calculation then change the ratio to 100% then you get the percentage of the glycerin at the end.

    Thanks, Pharma!

    I just have to decide whether I want to lower the amount of the fatty acids that I am using to replace one of the oils and add back the difference in glycerin while adjusting the amounts of NaOH and KOH based on the lower amounts of the fatty acid used or whether I could just leave them as they are and add more glycerin.  Either way, as the author of Harry's Cosmeticology said about making shaving cream "it is very much an art"!


  • PharmaPharma Member, Pharmacist
    The best math formula is always the one which works best for you (as long as the result is correct :) )!
    I don't know if it's important in your case but the % is relative to oil, not soap. The % in soap would have to be calculated from mg/g, ounces/ounces or spoon/pint by calculating mg glycerol and weighing the obtained soap corresponding to 1 g oil.

    I did some quick&dirty saponification and jup, if you want more than a simple chemical reaction, it's not just done by mixing ingredients. It always looks so simple! During my studies, we also did saponification reactions where we had to titrate and back-titrate to determine the exact saponification value for the oil at hand. Not that it would have mattered, since the end product was an greasy/tacky/ugly/greyish ointment anyway LoL.
  • BelassiBelassi Member, PCF student
    I did consider using FFA's as part of the oils to reduce the amount of glycerin produced and hopefully limit sweating, but then another problem occurs: the reaction time shortens to the point that no 'artwork' can be done, and worse, a high probability of 'ricing' due to the lye reacting preferentially with the FFA's.
    Cosmetic Brand Creation. Concept to name to IMPI search to logo and brand registration. In-house graphic design inc. Pantone specs. Cosmetic label and box design & graphics.
  • PharmaPharma Member, Pharmacist
    Did you consider using ester oils or waxes/jojoba?
  • BelassiBelassi Member, PCF student
    ester oils or waxes/jojoba?
    -- The expense!!!
    Cosmetic Brand Creation. Concept to name to IMPI search to logo and brand registration. In-house graphic design inc. Pantone specs. Cosmetic label and box design & graphics.
  • PharmaPharma Member, Pharmacist
    Right, I always forget about $$$. Sorry, hobby formulator with a piss poor economic judgement here :) .
  • Belassi said:
    I did consider using FFA's as part of the oils to reduce the amount of glycerin produced and hopefully limit sweating, but then another problem occurs: the reaction time shortens to the point that no 'artwork' can be done, and worse, a high probability of 'ricing' due to the lye reacting preferentially with the FFA's.
    That would depend upon the Fatty Acids chosen!  Olive oil is often used in handcrafted soaps and that typically contains 82%-83% Oleic Acid which does produce a hard bar but does not speed up the saponification process the way a fatty acid like stearic acid would!  Choosing a moderately large amount of that, palmitic acid and coconut fatty acid in a somewhat smaller amount (20% to 30% range) might produce soap with no problems.  Also, another thing would be the lye solution strength which could be changed to make the process slower as well...  I think it's possible!
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