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. The long chain fatty acids found in fats have low saponification value because they have a relatively fewer number of carboxylic functional groups per unit mass of the fat as compared to short chain fatty acids. 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

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

Handmade soap makers who aim for bar soap use NaOH sap values which are derived from the saponification value calculated by laboratories (KOH sap value). To convert KOH values to NaOH values, divide the KOH values by the ratio of the molecular weights of KOH and NaOH (1.403).

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

[edit] See also

• Acid number
• EN 14214
• Iodine number
• Saponification

[edit] External links

• Therese Lott's Saponification Calculator - Standalone spreadsheet for calculating saponification values in handmade soapmaking.