Thursday, 19 May 2016

Understanding SAP Values and Superfatting

Saponification value is the required amount of lye needed to saponify 1000gm of oil.  This is to change fatty acids it to a glycerol and salt of the acid that is in that particular oil = Soap.

Recently I was trying to find the saponification value for Carauba Wax.  I found that it was between 81-95.  I was looking for a number that was more like 0.1 -0.09 so it confused me and took a lot of searching for the answer, till I found one web site that explained it was per 1000gm of oil and is for Potassium Hydroxide (potash).
(They also have a comprehensive chart with SAP values for oils.)

To get it for Sodium Hydroxide (hard bar) you have to divide this number by 1.4025.    This will now be the NaOH needed for 1000gm,  To get it to your lye/gram oil ratio just divide it by 1402.5 . Now you can then multiply for each gram of oil.

Remember that there are seasonal and geographical differences in Oil saponification values and also the strength of the lye whether NaOH or KOH may vary slightly according to manufacturer.  This is one of the reasons soap makers recommend having a super fat (excess oil) of approximately 5%.

There is also a reasonable possibility that the Olive oil you use is not pure regardless of the label.  Even experts can't tell the difference by taste or appearance.  If Canola oil was used to dilute the Olive Oil this would result in a 2 gram difference in lye needed for 1000gm of Oil.  While this isn't much, combined with the other possible variations it could tip the lye balance over if you don't have a moderate super fat.

Yes the superfat is probably the main culprit for the build up in your sink.  It's the price to pay for moisturised skin.

Happy soaping

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