Soap Making: Saponification and SAP Values
Posted on July 19, 2016.
Saponification is the chemical process that turns fat into soap by combining the fats with either potassium hydroxide (KOH) or sodium hydroxide (NaOH) also known as lye. Potassium hydroxide and sodium hydroxide are both alkalis.
All of the different types of fats (olive oil, coconut oil, palm oil, mango butter, cocoa butter, etc.) have a saponification value assigned to them. These saponification values are also known as a "SAP value." This SAP value equates to the number of milligrams of KOH (potassium hydroxide) it takes to convert or "saponify" a fat into soap. It is the average molecular weight of the amount of fatty acids present. This is the industry standard for SAP values.
Because SAP values are listed as KOH, the value must be converted from potassium to sodium in order to make bar soap. Potassium hydroxide will only make liquid soap. To convert, divide the average SAP value by the ratio of the molecular weight of KOH, which is 1.0, or by the molecular weight of NaOH, which is 1.403. Once you have this conversion ratio, which we have provided for you in the description for most of our oils, calculate the amount of lye you will need in a recipe by multiplying the total amount of fat by the converted ratio. Here are a couple of examples of this calculation:
Liquid Soap Calculation:
48 grams of Coconut Oil x .1900 (converted SAP value of coconut oil for KOH) = 9.12 grams of NaOH (potassium hydroxide)
Solid Bar Soap Calculation:
48 grams of Coconut Oil x .2660 (converted SAP value of coconut oil for NaOH) = 12.768 grams of KOH (sodium hydroxide)
Note: When making soap, we recommend to measure your lye and fats using a digital scale that measures at least out to 2 decimal places. It is very important that your measurements by weight are very accurate, as it is a very specific chemical process. Also, it is important to make sure that you use the same units to measure by weight. For instance, if you are measuring in grams, make sure to measure both the fats and lye in grams instead of measuring one in grams and one in ounces.