Determining SF + Lye Discount?

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Mestiza Girl

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Hellooo my fellow soap makers. I've read in a few threads that determining SF is totally up to you based on your preference. However I've also read that certain oils or butters pair well with lower/higher SF. I've also briefly seen SF associated with the term "lye discount".. would someone please clearly define lye discount & explain the correlation between the two? And what helps you determine your SF percentage?
 

DeeAnna

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Let's say you have a soap recipe that needs (picking numbers out of the air) 120 grams of NaOH to exactly saponify 450 grams of fat. When you make this recipe, there is no excess fat and there is no excess lye.

Strictly speaking -- To superfat the soap, you'd use the same 120 grams of NaOH, but you'd use more fat than 450 grams -- maybe 475 grams. The extra 25 grams of super (additional) fat will not saponify.

To do a lye discount, you'd use the original 450 grams of fat, but you'd use less NaOH, maybe 115 grams, instead of the full 120 grams. Again, using less lye means there is some fat left over that won't be saponified.

You add fat in the superfatting method and you take away lye in the lye discount method. The batch size increases when using the superfatting method -- the fat weight increases. The batch size decreases with the lye discount method -- the lye weight is reduced.

The unsaponified fat, regardless of the mathematical gyrations used, becomes the superfat in the finished soap.

Now that I've defined the strict definitions of these concepts, I have to say most people most of the time talk about superfat and lye discount if they are totally interchangeable. The soap recipe calcs do likewise. Most of us and most of the calcs are doing a lye discount calculation, but we aren't too strict on the terminology -- we might call it a lye discount or we might call it a superfat.

A lot of bath soap recipes nowadays seem to be superfatted from 2% to 8%, more or less. When I first started soaping in 2012, I seem to recall many people used somewhat higher superfats -- maybe closer to 5%-10%. There are hot trends in soap making just like anywhere else.

There are some soaps that are exceptions to this 2-8% superfat range. Probably the best known exception is the 100% coconut oil soap. If used for bathing, most people superfat this soap in the 15% to 20% range.

I have some more info here: https://classicbells.com/soap/superfat.asp
 
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Mestiza Girl

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Let's say you have a soap recipe that needs (picking numbers out of the air) 120 grams of NaOH to exactly saponify 450 grams of fat. When you make this recipe, there is no excess fat and there is no excess lye.

Strictly speaking -- To superfat the soap, you'd use the same 120 grams of NaOH, but you'd use more fat than 450 grams -- maybe 475 grams. The extra 25 grams of super (additional) fat will not saponify.

To do a lye discount, you'd use the original 450 grams of fat, but you'd use less NaOH, maybe 115 grams, instead of the full 120 grams. Again, using less lye means there is some fat left over that won't be saponified.

You add fat in the superfatting method and you take away lye in the lye discount method. The batch size increases when using the superfatting method -- the fat weight increases. The batch size decreases with the lye discount method -- the lye weight is reduced.

The unsaponified fat, regardless of the mathematical gyrations used, becomes the superfat in the finished soap.

Now that I've defined the strict definitions of these concepts, I have to say most people most of the time talk about superfat and lye discount if they are totally interchangeable. The soap recipe calcs do likewise. Most of us and most of the calcs are doing a lye discount calculation, but we aren't too strict on the terminology -- we might call it a lye discount or we might call it a superfat.

A lot of bath soap recipes nowadays seem to be superfatted from 2% to 8%, more or less. When I first started soaping in 2012, I seem to recall many people used somewhat higher superfats -- maybe closer to 5%-10%. There are hot trends in soap making just like anywhere else.

There are some soaps that are exceptions to this 2-8% superfat range. Probably the best known exception is the 100% coconut oil soap. If used for bathing, most people superfat this soap in the 15% to 20% range.

I have some more info here: https://classicbells.com/soap/superfat.asp
Thank you DeeAnna, that helped a ton. Any reason in particular why a coconut oil soap would have such a high percentage of SF? Is SF visible on the soap? I hear that high percentages reduce lather.
 

DeeAnna

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Coconut oil (CO) soap with a moderate to low superfat can easily strip too much of the natural fats and proteins from the surface of the skin. If you wash with a 100% CO soap made with low superfat, you're likely to see your skin look ashy and your skin will feel overly dry or tight. The high superfat basically interferes with this stripping action, so the soap feels milder to the skin.

Superfat is not visible in or on solid bar soap as long as the superfat % is within reason for that particular soap. A high or 100% CO soap at 20% superfat looks and acts perfectly fine. But a 100% olive oil soap at 20% superfat might be overly soft and could have a greasy feel.

Yes, lather tends to be less when you add more superfat, but again, you have to consider the context and keep your other goals in mind. For example, I think mildness wins out over lots of lather for most people, so a soap maker might have to find an acceptable balance between the two. A coconut oil soap is highly soluble in water, so it lathers pretty good even with a high superfat and the extra superfat is needed to tame down this type of soap to a tolerable mildness.

Other, more typical soap recipes will show a reduction in lather as the superfat goes up, so the acceptable balance between mildness and lather might be at a much lower superfat -- if the soap is already nicely mild at, say, 5%, then why increase the superfat? Maybe it could go even lower? The Lather Lover's soap swap showed an increase in lather when the superfat was decreased from 8% down to 5% with otherwise the same recipe. Compare test 1 and test 1A here: https://www.flickr.com/photos/amathiasoapworks/6878518116/in/set-72157629324839760/
 

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