HP: Why don't we superfat by adding acids after saponification?

[paragon]

I read in a book that at larger scales, soap is often superfatted by making it neutral or with lye excess, then adding acid (sulfuric, hydrochloric, or boric) to create some sodium salt and free some fatty acids. Is there any reason we don't do it that way? I was thinking I could use citric and acetic acid and kill three birds with one stone:

• sodium citrate will act as a mild chelating agent
• sodium acetate will harden the soap, similar to sodium lactate
• fatty acids will be freed to make superfat

The primary difference between this method and the more common lye discount is that the acid addition will be composed of glycerides while with this method it will be free fatty acids. Other possible advantages I foresee:

• lard smell will probably be removed because there will be no unreacted compounds
• DOS might be less likely for the same reason

Is there any reason this isn't commonly done? Any disadvantage to having free fatty acids as the superfat?

 

[Millie]

I would love to hear how it goes if you try this. Especially if the lard smell is eliminated!

 

[DeeAnna]

"..Is there any reason this isn't commonly done?..."

It isn't commonly done by small-scale soap makers because we have the fats on hand, but most soap makers don't usually have fatty acids on hand. You can even make soap with all fatty acids -- no fat at all -- if that's what you want to do. There are methods/recipes here for shave soap, cream soap, and some liquid soap that are basically superfatted with fatty acids, usually stearic acid.

"... Any disadvantage to having free fatty acids as the superfat?..."

There's no real disadvantage except the need to source and stock these extra ingredients.

"...the acid addition will be composed of glycerides..."

If you add acid to a neutral* finished soap, the resulting superfat will be fatty acids, not glycerides.

* Neutral meaning no excess fat, no excess alkali.

 

[paragon]

If you add acid to a neutral* finished soap, the resulting superfat will be fatty acids, not glycerides.

This is what I meant. I don't have fatty acids on hand either, but I'm planning to add some acids to a HP soap which will preferentially react with the lye leaving free fatty acids, though I know the chemistry is a actually a bit more complicated since the salts don't form bonds when dissolved. Since I will formulate with a lye excess I won't be able to use the zap test to see when it's done reacting, but a few hours post gel-phase in a well insulated thermos-type pot will make me sure enough.

 

[DeeAnna]

If you add sufficient acid to react with the lye excess as well as to decompose some of the soap, the zap test will work.

I am not sure that's what you're trying to explain, however -- I'm getting a little lost trying to follow the verbiage.

You're using technical words, but you're using them in a less-than-precise way. That's confusing. It would be best if you used shorter sentences and plain language.

Here's an example --
"...I'm planning to add some acids to a HP soap which will preferentially react with the lye leaving free fatty acids..."

The acids you mention -- citric acid and vinegar (acetic acid) -- do not react with lye to make fatty acids. They make sodium citrate and sodium acetate. It's the reaction of these acids with soap that create fatty acids.

 

[paragon]

If you add sufficient acid to react with the lye excess as well as to decompose some of the soap, the zap test will work.

Yet I cannot add the acid until saponification is complete, if I want to achieve the effect I'm going for: no unreacted oils or other reactive animal/vegetable matter. I mentioned the zap test with respect to the question of when saponification is complete.

I'm getting a little lost trying to follow the verbiage.
"...I'm planning to add some acids to a HP soap which will preferentially react with the lye leaving free fatty acids..."

Forgive me. I meant that I will add acids to soap (acetic and citric added to fatty acid salts, glycerin, and water). I don't know the proper terminology to explain the reaction at that point. I would like to say the bond between some Na+ and fatty acids will be broken and the citric and acetic acid will bond the Na+ instead (leaving free fatty acids), but I'm not sure if that's correct terminology/description, due to ionic bonds being kind of funny in solution.

 

[DeeAnna]

"...I don't know the proper terminology to explain the reaction at that point...."

And that's my point -- you're trying to explain science you do not fully understand. It is only confusing people, not helping. This is the second post in which you've had to correct your words. Best to stick to the facts you understand and know to be correct rather than guess and be wrong.

 

[paragon]

It seems like you have not been on the same page as the rest of us since the first post. Though I appreciate your feedback, my imprecision is clearly not the only problem here.

And that's my point -- you're trying to explain science you do not fully understand. It is only confusing people, not helping.

Is your way better? You wrote that acid "degrades" soap. That is not what happens at all.

Note: despite this disagreement, I do appreciate the answer you gave above (that there is no disadvantage to superfatting with fatty acids).

 

[DeeAnna]

Hmm. Except for Millie, there is no "rest of us" in this thread besides you and me. Or maybe I'm missing them too. Glad I could answer your questions despite being so abysmally bad at understanding what you want to know.

 

[Mobjack Bay]

@paragon In the spirit of learning, I hope you give this a try. Soap chemistry is so dang complicated that I expect to be learning something new everyday for the rest of my life. One question I have is why a free fatty acid would be less prone to DOS than a fatty acid in a triglyceride, if that’s what you’re suggesting in post #1.

 

[Millie]

I am way behind all of you. With two scientists in the thread already and an adventurous and curious OP, I think a lot could be learned in this thread for those of us who don't really have the knowledge to contribute, but are watching from the sidelines.

What would be the difference between a soap superfatted this way and a soap superfatted the traditional way, but with sodium citrate and sodium acetate as additives?

 

[paragon]

I found out why no small scale soap makers superfat by acidifying. With no superfat (pre-acidification stage), soap is very solid (unless you used KOH, of course). Even when hot, it breaks into a crumbly mess. It does not melt into a gel as our more usual recipes do. A few hours after making the soap, adding the acids was like rebatching. It did not mix. I had to mush it all together with my (gloved) hand, though it was still hot enough to be uncomfortable through the glove. This was despite the recipe having 35.5% water PPO, which is not terribly low. (That came to a 2:1 water:lye ratio because I used a large lye excess.) Remember, at the crumbly stage, no acids were yet added, so hardness can't be attributed to sodium acetate. I just added more water and heated it.

Other notes: trace happened within three minutes and gel phase within five. Fats were 60% lard, 15% olive, 12% canola, 10% coconut, and 3% castor oil. The choice of oils might seem to explain why it's so hard, but I've made other HP soaps from hard oils, and they are not hard when hot (even the next morning). The difference is that this one has absolutely no SF in the first stage. Also, this recipe might not lather well, so I added 0.83% sugar PPO.

What would be the difference between a soap superfatted this way and a soap superfatted the traditional way, but with sodium citrate and sodium acetate as additives?

An acid-superfatted soap would have let the oils react with lye more completely. It would produce a couple percent more glycerin, and everything else (proteins?) that could react with lye would do so. That's why I thought it would reduce DOS: if impurities are involved, maybe they would be destroyed by the excess lye. With normal SF soap, there is no excess lye.

Edit: Total oils: 300 g. Water: 105 g. NaOH: 50.6 g. Hot process, cooked on low heat until gel phase. Additions some hours after gel phase: 4.5 g glacial acetic acid, 7.5 g citric acid, 10 g water, 2.5 g sugar.
After mixing in the last ingredients plus extra water (at least 20 g extra), the soap became even thicker. I kneaded to break up lumps and get the acids evenly distributed, then put the soap in a double boiler to hopefully melt it again. This acidification plan might have worked if I had cooked at higher temperature and if I had left it on the cooker the whole time, never letting it harden.

Edit 2: after remelting everything it became a cream. Additional snag: the soap fractionated. I kept finding darker yellow waxy looking bits and stirring them back in. I hope this has no effect. I spooned the custard-textured soap into my mold.

Verdict on the smell: it smells like lard-based soap but not at all like the lard that went into it. I count that a success. However, the procedure is bad, needing more heat and more water than other HP soaps. (Aside: I wonder how this compares to using sodium lactate in HP soap.) A better way to avoid lard odors is to use better smelling lard and process the soap at a low temperature.

 

[Mobjack Bay]

@paragon it sounds like you were very busy with what turned out to be a methodologically challenging experiment.

I had asked about DOS because it’s something I’ve been thinking about a lot lately after finding a couple of spots on my soaps from the summer. From my reading, DOS in artisan soap is mainly attributable to the practice of superfatting, the use of unsaturated fats and the presence of catalytic metals ions, especially from tap water or contamination. Each increases the potential for oxidation of the unsaturated FAs (from Kevin Dunn’s Scientific Soapmaking, e.g. pg 285 and other sources). In addition, from reading here on the forum, making soap with old oils jump starts DOS. The citric acid you added would help to chelate any metals. I don’t think you need to worry about proteins, especially not from the oils. Milk is quite commonly added to soap and I don’t recall it being linked to DOS, except perhaps over an extended period of time. In any case, if your fats are refined, most proteins have been removed. If you used pomace olive oil, you may have unsaponifiables, but those would be waxes, esters, etc. Heat is a variable that I am increasingly considering in my soap making. It increases the rate of oil oxidation (see recent discussion, here), but is rarely brought up in discussions of factors that might increase the chances of DOS. In theory, it would be increasingly problematic as the percentages of PUFAs and then MUFAs increase in recipes. I don’t know enough chemistry to know if free fatty acids are more or less prone to oxidation compared with fatty acids in triglyceride molecules. If you come across anything on that topic, please let me know.

 

[paragon]

From my reading, DOS in artisan soap is mainly attributable to the practice of superfatting, the use of unsaturated fats and the presence of catalytic metals ions, especially from tap water or contamination. Each increases the potential for oxidation of the unsaturated FAs (from Kevin Dunn’s Scientific Soapmaking, e.g. pg 285 and other sources). In addition, from reading here on the forum, making soap with old oils jump starts DOS. The citric acid you added would help to chelate any metals. I don’t think you need to worry about proteins, especially not from the oils...

It's hard for me to wrap my head around spoilage that's not caused by microbial contamination, so I incorrectly assumed nutrients or microbes were involved and that more sterile soap would reduce the problem (with lye being a rather good sanitizer). I'm reading more about it now. You've probably already come across this interesting article--I think I've seen it linked on this forum:

https://www.wholesalesuppliesplus.c...les/orange-you-glad-the-chemistry-of-dos.aspx

So based on that, I have no reason to think this procedure would help. However, if superfatting causes DOS, does that mean triglycerides are more vulnerable than FAs? I wouldn't count on that until I've read more.

 

[Mobjack Bay]

@paragon you can forget about microbial processes for the most part, unless you start making your soap with chunks of organics. We discussed the pH of soap and microbes not that long ago. See the links to posts below. The the article you linked is by Kevin Dunn, the author of the book I mentioned above. He literally “wrote the book” that most rely on for understanding artisan soap chemistry. The other notable expert on soap making methods and the chemistry behind what we do is DeeAnna Weed. The Soapy Stuff website linked in her posts (see above) is a goldmine of useful information. I’m no where near reading everything she’s posted here on the forum, but it’s a goal.

[URL]https://www.soapmakingforum.com/threads/sea-water-for-soap.75076/page-2#post-771262
https://www.soapmakingforum.com/threads/sea-water-for-soap.75076/page-2#post-771860[/URL]

 

[paragon]

@paragon you can forget about microbial processes for the most part, unless you start making your soap with chunks of organics. We discussed the pH of soap and microbes not that long ago. See the links to posts below...

That's an interesting discussion, thanks. It doesn't apply to microbes in the oil phase, however. The pH of unreacted oil (SF) won't change. I'm sure cooking oils aren't that contaminated but I doubt they're sterile, either.

Given that the smell reduction is the only reason to do this procedure, next time I'll modify it: I will completely saponify the lard, using the recipe's full amount of lye and water. Next I will add any acids that are called for. Next I will add the other oils. There will not be a lye excess at this stage, so mixing/melting will be easier compared to mixing a non-superfatted soap.

 

[Mobjack Bay]

That's an interesting discussion, thanks. It doesn't apply to microbes in the oil phase, however. The pH of unreacted oil (SF) won't change. I'm sure cooking oils aren't that contaminated but I doubt they're sterile, either.

Once the soap is made, every surviving microbe, as well as any FFAs or unsaponifiables will be in an environment that is on average pH 10 or close I suppose there could be micro zones of lower pH, but is there any reason to expect conditions would be conducive to microbial growth in that situation?

 

[paragon]

Once the soap is made, every surviving microbe, as well as any FFAs or unsaponifiables will be in an environment that is on average pH 10 or close I suppose there could be micro zones of lower pH, but is there any reason to expect conditions would be conducive to microbial growth in that situation?

No, I have no reason to think that's a problem (in a solid product). It was just a bad guess about something I didn't research properly.

That said, I'm still attracted to the idea of zero superfat during saponification due to the fact that it's a chemical reaction run to completion and the result should never differ based on stirring or temperature. I may try this again, next time neutralizing with an acid that I expect to not increase the soap hardness while melted. Or if I'm feeling daring, I could use a bit of ammonia in place of lye and let some of that evaporate to leave free fatty acids in the soap. Though I'm not a manufacturer, so I don't need guaranteed uniformity in every batch.