How Much Glycerin in Handmade Soap?
I have been asked about the glycerin content of soap made with various oils. Here is some information that might be helpful in figuring this out.
First of all the glycerin recovered from commercial soaps is 80% (that does not mean that soap contains 80% glycerin, but that the recovered glycerin isn’t exactly pure.) After glycerin is recovered from commercial soaps, it is distilled into a purer form.
Okay, that said, here is a list of the available percentages of 80% glycerin contributed to soap by some of the different oils which may be used in the making soap making process according to Modern Soap and Glycerin Manufacture, by E.T. Webb.
18% - Coconut
18% - Palm Kernel Oil
13% - Cottonseed Oil
13% - Soy Bean Oil
13% - Olive Oil
13% - Lard
12.5% - Tallow
12.5% - Castor Oil
12% - Palm Oil (bleached)
When figuring out the percentage of glycerin in your soap you will also have to take into account the percentage of lye, water, and any other additives like herbs, color or fragrance used in the recipe and some how figure how much water evaporates from your soap.
You can figure out how much water evaporates by weighing your soap at the end of the cure period. Water weighs the same in volume as it does in weight, so 4 liquid ounces of water will weigh 4 ounces. Whatever amount of weight your soap loses during the cure period, you will have to subtract that from you recipe to get the correct percentages for the ingredients of the recipe or formula.
Sorry, you’ll have to do your own math.
Also remember that these numbers will simply give you an idea of how much glycerin is in a particular soap. Just like saponification numbers of various oils, glycerin percentages will also vary from crop to crop depending on growing conditions and other things. So, your milage may vary.