The concept of adding ingredients to add properties to our biodiesel glycerin (BDG) soap is something I introduced some time ago and have been pioneering over the last several years. In fact it is the basis of my book "Making Biodiesel Glycerin Soaps".
Basic Saponified Glycerin is where it starts -- You mix a caustic solution and add it to some demethed glycerin. Biodiesel glycerin soap 101... We love it but it's a tough sale getting others to share the same enthusiasm. Especially your female significant other.
A comment early on from my wife; "There is no way you are going to get me to rub that slimy piece of liver on my body". From that moment on I set out to make a better soap from our biodiesel glycern.
If you have the luxury of making your biodiesel out of saturated oils such as Lard, Tallow, Coconut Oil, Palm Kernel oil or Saturated Vegetable Oil you may find that your bar soap is already hard enough. But those oils make for biodiesel that can gel at pretty high temperatures. Summer fuel for most unless you live in the tropics.
Another battle in our bar soaps is the tendency of BDG bar soap to sweat. This is because of the high glycerin to soap ratio.
To combat soft sweaty bar soap you can add hardening ingredients. These ingredients include; Lard, Tallow, Coconut Oil, Palm Kernel Oil, Vegitable Shortening or pure fatty acids. All of these come with their strong points and their week points.
When using Lard, Tallow, Coconut Oil, Palm Kernel Oil or Vegetable Shortening you will need anywhere from 40% - 60% of these ingredients to get a really hard bar that does not sweat. A mix of these whole oil ingredients is best, that way you can use inexpensive lard, tallow or shortening to add hardness and coconut oil and palm kernel oil to add some nice lather to your soap. At 40% - 60% saturated oil to BDG you start to reduce sweating and harden the bar.
When using the pure (saturated) fatty acids (Lauric, Myristic, Stearic and Palmitic) you only need 10% - 20% of these ingredients. These bars are super hard and do not sweat. A blend of these saturated fatty acids will allow you to add both hardening and lathering properties.
Both Whole Oils and Pure Fatty Acids greatly improve both your bar and liquid soaps. This is because you are using the ingredients to balance your BDG soap. You could do something similar if you had access to both Saturated BDG and Unsaturated BDG -- except to reduce sweating.
Why does it take more Whole Oil ingredients to do the same job that pure (saturated) fatty acids do?
This is because the whole oil ingredients also introduce more glycerin and unsaturated fatty acids to the mix.
Let's use Lard as an example. It has tremendous hardening abilities. In fact it's been the staple of soap making since your Grandmother's time. But it also has unsaturated fatty acids. So by using lard in BDG soap you are also adding more glycerin and unsaturated fatty acids to your soap. So in effect along with adding hardening properties you are adding more soft soaps and glycerin. That's why it takes somewhere between 40% and 60% of a whole oil ingredient.
This is the fatty acid profile for lard.
As you can see if you were to have a whole oil that had only Palmitic, Stearic, Myristic and Lauric acid you would need much less of it. Coconut Oil and Palm Kernel Oil come very close but can be drying if you have too much of them in your soap.
Why not make your own "whole oil"? That's loosely what you are doing when you use the pure fatty acids. With pure fatty acids you have the ability to tailor which properties you add to your soap.
You can achieve similar results using whole oil ingredients and pure fatty acids. You can also make a blend of whole oils and/or fatty acids to tailor a terrific soap.
Always use the SAP value associated to your ingredients when adding them to your BDG soaps and be sure you have worked out a valid SAP value for your own glycerin. This way you can be sure that your soap is not caustic hot and will not go rancid due to greater than 5% superfatting.
And I can not stress enough... Check the final pH of your cured or hot processed soap. The pH should be between 9 and 10.5.
NEVER USE CAUSTIC SOAP!
Check out our recipes section to help you get started using whole oil and pure fatty acids in your soaps.
Happy Soaping.This message has been edited. Last edited by: Rick K,
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