Residue from yoghurt

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Saintlysoaper

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Hi all

I have noticed in my recent batches of soap ( now 4-6 weeks old) that if I repeatedly wash my hands with them, say, three times in a row ( while I was assessing lather etc) they leave a small amount of smooth white residue on my skin. The only way I can describe it is that it's like when you add a bit too much clay to a soap. Has anyone experienced this from adding a fair amount of yoghurt (50% water substitution) to a CP soap?

It's not drying as such it just leaves a whitish cast to the skin and feels just a little bit 'coated'.
 
My experienced guess is that it is most likely soap scum, which is typical with lye-based soaps, especially if you have hard water. The minerals in hard water react with soap to produce an insoluble soap (known as scum), which shows up as a white powdery film. I myself have hard water and am quite familiar with soap scum. To combat it, I add a little tetrasodium edta, a chelator, to my soap formulas. I use it at a rate of .5% as per the total weight of my entire batch. It hasn't totally eliminated the scum 100%, but it sure has eliminated a good portion of it.


IrishLass :)
 
Thanks Irishlass

I haven't experienced it with any of my previous soaps just these with yoghurty ones. I definitely live in a hard water area though and these are the least cleansing soaps I have ever made. Will that increase the effect?
 
When you say "yogurt residue" do you mean the leftover acidic whey?

If so, all that should really do is combine the lactic acid in the whey with a bit of the lye to create sodium lactate (which many of us add intentionally to harden soaps) while increasing your superfat just a bit. The effect should not be much - especially with only 50% substitution - because acidic whey only typically runs about 7% lactic acid at most. For instance, in my 40oz loaf using 370g of water normally, substituting 50% with whey would provide about 9 grams of lactic acid to "use up" lye an increase superfat. That translates into around 3/4% superfat difference.

TL;DR - It's probably not the whey.
 

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