When it comes to making soap, it's all about the lye to fat ratio, and exact measurements are key. You need a specific amount of lye to properly saponify a certain amount of fat. And every fat requires a different amount of lye. The SAP value, or saponification value, of a fat (plant or animal) represents how many milligrams of lye it takes to saponify one gram of that fat with no fatty acids remaining.
Saponification is the chemical reaction between a fatty acid and a lye molecule which produces soap and glycerine. Superfat refers to the percentage of fatty acids left over after the saponification process is complete. A 0% superfat means that essentially no fat remains. Compared to a 5% superfat where 5% of the original amount of fat is still present in the soap. SAP values are always intended to create a 0% superfat. Since SAP values fall within a range based on the environmental conditions the fat was produced in and how it was processed, the following chart offers an average of those values to ensure that all lye is converted into soap.
Learn how to calculate formulas using SAP values, check out Create Your Own Soap Recipes
For more on the process of making soap, see Cold Process Basics
Below is a list of common fats and their SAP values. The first column contains the common usage name(s) of fats. The second column gives the SAP value for Sodium Hydroxide. This is the amount of NaOH needed to convert one ounce of that fat to make solid soap. The third column gives the SAP value for Potassium Hydroxide, which is the amount of KOH needed to convert one ounce of that fat when making liquid soap.
For easy reference, you can also download or print the PDF version here.
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