Saponification value

Saponification value (or "saponification number", also referred to as "sap" in short) represents the number of milligrams of potassium hydroxide or sodium hydroxide required to saponify 1g of fat under the conditions specified. It is a measure of the average molecular weight (or chain length) of all the fatty acids present. As most of the mass of a fat/triester is in the 3 fatty acids, it allows for comparison of the average fatty acid chain length.

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If more moles of base are required to saponify N grams of fat then there are more moles of the fat the chain lengths are relatively small, given the following relation:

 Number of moles = mass of oil/relative atomic mass

Handmade Soapmakers who aim for bar soap use NaOH sap values, which are derived from the saponification value calculated by laboratories (KOH sap value). To convert NaOH values to KOH, multiply by the ratio of the atomic weights of Potassium and Sodium, or about 140%.

Standard methods for analysis are for example: ASTM D 94 (for petroleum) and DIN 51559.

The calculated saponification value is not applicable to fats and oils containing high amounts of unsaponifiable material, free fatty acids (>0.1%), or mono- and diacylglycerols (>0.1%).

See also

• Acid number
• EN 14214
• Iodine number
• Saponification