Milk soap acids post saponification?

[desiredcreations]

This may not be a beginner question, but I'm dying of curiosity and riddled with confusion.

Soap is defined, chemically, as a salt because the fats used are [fatty] acids and the sodium and potassium lyes are strong alkalis. Acids and alkalis will typically produce salts when mixed together.

Milk has lactic acid in it. When milk is used in a soap recipe, the lye reacts with lactic acid to produce sodium lactate.

Yet, there are soap makers that like to claim milk soap is good for the skin because of the lactic acid in the milk. If the saponification is complete, wouldn't acids and alkalis in the soap be converted into salts?

I saw a few other videos claiming to have made apple cider vinegar soap. Same issue. Wouldn't the acid have been converted into a salt, if the reaction follows basic chemistry?

Is there any good info to confirm or dispute my assumptions?

 

[DeeAnna]

"...milk soap is good for the skin because of the lactic acid in the milk. If the saponification is complete, wouldn't acids and alkalis in the soap be converted into salts?... apple cider vinegar soap. Same issue. Wouldn't the acid have been converted into a salt, if the reaction follows basic chemistry?..."

Yes, you're correct; the acids are converted into the salts. A college freshman level chemistry book will provide info about acid-base neutralization reactions, which is what's happening here.

If you have a pH meter, make a solution of lactic acid or citric acid or vinegar (acetic acid), insert the pH meter into the acid solution, and then add NaOH solution, drop by drop, while stirring. Watch the pH rise from the original pH of the acid. When the pH is neutral, the acid is neutralized with the base. The result is the salt of the acid and the alkali.

Somewhat the same process happens when you include soap in the mixture, except the soap acts as a buffer to modify how fast the pH changes in response to added acid or added alkali. But you still end up with the acid (lactic, acetic or citric) being neutralized into sodium acetate, sodium citrate, or sodium lactate.

If you're wanting info to convert those who believe otherwise, you might want to have a careful think about that. Most soap makers who believe there is intact vinegar or lactic acid or citric acid in their finished soap don't really want to hear otherwise.

 

[desiredcreations]

"...milk soap is good for the skin because of the lactic acid in the milk. If the saponification is complete, wouldn't acids and alkalis in the soap be converted into salts?... apple cider vinegar soap. Same issue. Wouldn't the acid have been converted into a salt, if the reaction follows basic chemistry?..."

If you're wanting info to convert those who believe otherwise, you might want to have a careful think about that. Most soap makers who believe there is intact vinegar or lactic acid or citric acid in their finished soap don't really want to hear otherwise.

Thank God you replied! Thank you so much, DeeAnna. After seeing so many clueless soapmaking videos and recipes, I was beginning to doubt my decades of education and experience on the basics of chemistry!

I won't bother with converting, unless I'm feeling especially smart-assy. I'll try to use my energies in better pursuits. ;-)

 

[lenarenee]

"...milk soap is good for the skin because of the lactic acid in the milk. If the saponification is complete, wouldn't acids and alkalis in the soap be converted into salts?... apple cider vinegar soap. Same issue. Wouldn't the acid have been converted into a salt, if the reaction follows basic chemistry?..."

Yes, you're correct; the acids are converted into the salts. A college freshman level chemistry book will provide info about acid-base neutralization reactions, which is what's happening here.

If you have a pH meter, make a solution of lactic acid or citric acid or vinegar (acetic acid), insert the pH meter into the acid solution, and then add NaOH solution, drop by drop, while stirring. Watch the pH rise from the original pH of the acid. When the pH is neutral, the acid is neutralized with the base. The result is the salt of the acid and the alkali.

Somewhat the same process happens when you include soap in the mixture, except the soap acts as a buffer to modify how fast the pH changes in response to added acid or added alkali. But you still end up with the acid (lactic, acetic or citric) being neutralized into sodium acetate, sodium citrate, or sodium lactate.

If you're wanting info to convert those who believe otherwise, you might want to have a careful think about that. Most soap makers who believe there is intact vinegar or lactic acid or citric acid in their finished soap don't really want to hear otherwise.

DeeAnna, are there any ingredients that aren't changed by lye: aloe, sugar, food, clay etc.?

 

[earlene]

Even though we know that soap is a salt, there are some things left over when all the lye is used up. And there are some things that lye does not convert to a salt, so they are also still in the soap (unless they evaporate off as gases, like water and some components in fragrances, for example). And often there is excess of the items that would have been converted to a salt if there had been enough lye to convert all of it, as in Super Fat. (Case in Point: when using the a superfat setting in your lye calculator of choice.)

In no way am I disputing your point and DeeAnna's expertise. You are obviously correct. I just wanted to point out that there are other things in the soap that remain and I believe that some soapmakers believe that some of those ingredients that did not get turned into the soap-salt is what makes their particular soap so superior to other soap.

And to some degree, there are perceivable differences, but I will concede the fact that perception is often, if not always dependent on personal (& most probably biased) influences, as in 'beauty is in the eye of the beholder'.

Perhaps there is a happy medium that can be reached when communicating with folks who lean more toward their own perception than toward scientific laws, facts, hypotheses or theories (the definitions of which are not what the general public generally perceives, by the way.)

 

[DeeAnna]

DeeAnna, are there any ingredients that aren't changed by lye: aloe, sugar, food, clay etc.?

This question gets asked a lot about various additives, including essential oils and "luxury" carrier oils with supposed skin or hair benefits (ex: argan oil). I avoid saying much, because there is no simple, clear-cut way to know, if only because the question is much too broad. To attempt an answer, you'd have to look at the individual chemical components in each additive and research the effects of alkali on each chemical component.

For example, "sugar" as everyday people call it isn't just one thing. As I think you know from your studies, there are various types of sugars. Some of these are called "reducing sugars' and others are non-reducing sugars. The reducing sugars do react with other chemicals in an alkaline environment, which is exactly what you've got in soap. Non-reducing sugars do not react.

That is why white sugar (cane or beet sugar) generally doesn't darken soap, since sucrose, a non-reducing sugar, is the main sugar in white sugar, although it's not necessarily the only sugar. On the other hand, lactose, the sugar in dairy milk, is a reducing sugar, which is likely one of the reasons why dairy milk tends to darken soap. But there are other chemical components in dairy milk so you'd have to evaluate those as well to have some idea what they do when used in soap.

As far as aloe. We know it has "sugars" but most of us don't know what types. What other chemical components are in the aloe?

And foods -- that's such a broad category, it's impossible to say much.

Moving on to clay -- From my studies in soil science, I know there are many types of clay with kaolin and bentonite being two that are familar to soap makers. Some clays can be highly reactive chemically, but clays, being products of nature, are also highly variable so they won't necessarily all function the same even if they're of the same type (ex: kaolin clay from various parts of the world). One thing I know can happen to clay -- The sodium ion (the Na in NaOH) is known to adsorb onto the layered surfaces within clay particles and "collapse" those layers so the clay doesn't function normally. That's why soil in the southwestern states of the US can become "salt poisoned" and non productive.

 

[desiredcreations]

Even though we know that soap is a salt, there are some things left over when all the lye is used up. And there are some things that lye does not convert to a salt, so they are also still in the soap (unless they evaporate off as gases, like water and some components in fragrances, for example). And often there is excess of the items that would have been converted to a salt if there had been enough lye to convert all of it, as in Super Fat. (Case in Point: when using the a superfat setting in your lye calculator of choice.)

Thank you. I like to dig deep when I get into a new activity. Last night I was thrilled to find this scientific study online about homemade soap and the saponification process. It will take me a while to absorb it all, but I like that kind of fun. According to this report:

https://www.ncbi.nlm.nih.gov/pmc/ar...rocess in,and moisturizing abilities of soaps
"Commercially, natural soaps are manufactured via either a cold or hot saponification process, where triglycerides in fats, oils, and/or free fatty acids used as feedstock are converted in the presence of a base (typically sodium or potassium hydroxide) to form fatty acid salts (soaps), glycerol, and free fatty acids [1,3]."

 

[earlene]

Thank you. I like to dig deep when I get into a new activity. Last night I was thrilled to find this scientific study online about homemade soap and the saponification process. It will take me a while to absorb it all, but I like that kind of fun. According to this report:

https://www.ncbi.nlm.nih.gov/pmc/ar...rocess in,and moisturizing abilities of soaps
"Commercially, natural soaps are manufactured via either a cold or hot saponification process, where triglycerides in fats, oils, and/or free fatty acids used as feedstock are converted in the presence of a base (typically sodium or potassium hydroxide) to form fatty acid salts (soaps), glycerol, and free fatty acids [1,3]."

I've seen that article before. I had to look up the word paucity, not a word I commonly come across. I'll bet my dad knew that word, but he wasn't around to ask, and as he always told me, look it up if you don't know it.

Anyway, yes it has a lot of technical information that can take a lot of time to absorb. I found it rather overwhelming myself, but I wasn't looking for anything in particular at the time. And a lot of it is beyond my level of chemistry education.

However, in the Conclusion section, I found what I think is most important information as it pertains to me as a soapmaker. And I quote directly:

"Appealing smell was the greatest influencer of consumer preference, while color and appealing smell were the best indicators of natural soaps’ estimated pricing and consumers’ perceived quality, and consequently acceptability. These findings are of major significance to artisanal production of natural herbal soaps because antioxidants, polyphenols, and unsaponified unsaturated fatty acids appear to be major determinants of natural soap quality, consumer perception, and preference of the final products. One of the most significant findings in this study was that the base bar used as control in this study had the best overall preference compared to the other soaps formulated with specialty or exotic plant oils as feedstock and additives. These findings suggest some of the more exotic additives and specialty oils used to manufacture hand-made natural soaps may not be producing the perceived consumer acceptance or preference, and that artisan natural soap makers should give careful considerations to their use during the manufacturing of hand-made natural soaps. This work provides some baseline information regarding natural hand-made soaps manufacturing, which is very sparse in the scientific literature. The hope is that the information presented will stimulate additional studies by other researchers in the scientific community, to further improve the knowledge that may be of value to the growing specialty hand-made soap industry."

Highlighting is not possible, so I bolded & italisized the parts that I found most important.

Still, as I said, this document is a bit above my head, so there may be a whole lot I am missing because I did not bother to try to comprehend what I felt I would probably not comprehend.

 

[lenarenee]

This question gets asked a lot about various additives, including essential oils and "luxury" carrier oils with supposed skin or hair benefits (ex: argan oil). I avoid saying much, because there is no simple, clear-cut way to know, if only because the question is much too broad. To attempt an answer, you'd have to look at the individual chemical components in each additive and research the effects of alkali on each chemical component.

For example, "sugar" as everyday people call it isn't just one thing. As I think you know from your studies, there are various types of sugars. Some of these are called "reducing sugars' and others are non-reducing sugars. The reducing sugars do react with other chemicals in an alkaline environment, which is exactly what you've got in soap. Non-reducing sugars do not react.

That is why white sugar (cane or beet sugar) generally doesn't darken soap, since sucrose, a non-reducing sugar, is the main sugar in white sugar, although it's not necessarily the only sugar. On the other hand, lactose, the sugar in dairy milk, is a reducing sugar, which is likely one of the reasons why dairy milk tends to darken soap. But there are other chemical components in dairy milk so you'd have to evaluate those as well to have some idea what they do when used in soap.

As far as aloe. We know it has "sugars" but most of us don't know what types. What other chemical components are in the aloe?

And foods -- that's such a broad category, it's impossible to say much.

Moving on to clay -- From my studies in soil science, I know there are many types of clay with kaolin and bentonite being two that are familar to soap makers. Some clays can be highly reactive chemically, but clays, being products of nature, are also highly variable so they won't necessarily all function the same even if they're of the same type (ex: kaolin clay from various parts of the world). One thing I know can happen to clay -- The sodium ion (the Na in NaOH) is known to adsorb onto the layered surfaces within clay particles and "collapse" those layers so the clay doesn't function normally. That's why soil in the southwestern states of the US can become "salt poisoned" and non productive.

I see what you mean! Yes, it sounds like a whole 'nother book would be needed for this topic.

 

[desiredcreations]

I've seen that article before. I had to look up the word paucity, not a word I commonly come across. I'll bet my dad knew that word, but he wasn't around to ask, and as he always told me, look it up if you don't know it.

Anyway, yes it has a lot of technical information that can take a lot of time to absorb. I found it rather overwhelming myself, but I wasn't looking for anything in particular at the time. And a lot of it is beyond my level of chemistry education.

However, in the Conclusion section, I found what I think is most important information as it pertains to me as a soapmaker. And I quote directly:

"Appealing smell was the greatest influencer of consumer preference, while color and appealing smell were the best indicators of natural soaps’ estimated pricing and consumers’ perceived quality, and consequently acceptability.These findings are of major significance to artisanal production of natural herbal soaps because antioxidants, polyphenols, and unsaponified unsaturated fatty acids appear to be major determinants of natural soap quality, consumer perception, and preference of the final products. One of the most significant findings in this study was that the base bar used as control in this study had the best overall preference compared to the other soaps formulated with specialty or exotic plant oils as feedstock and additives. These findings suggest some of the more exotic additives and specialty oils used to manufacture hand-made natural soaps may not be producing the perceived consumer acceptance or preference, and that artisan natural soap makers should give careful considerations to their use during the manufacturing of hand-made natural soaps. This work provides some baseline information regarding natural hand-made soaps manufacturing, which is very sparse in the scientific literature. The hope is that the information presented will stimulate additional studies by other researchers in the scientific community, to further improve the knowledge that may be of value to the growing specialty hand-made soap industry."

Highlighting is not possible, so I bolded & italisized the parts that I found most important.

Still, as I said, this document is a bit above my head, so there may be a whole lot I am missing because I did not bother to try to comprehend what I felt I would probably not comprehend.

"Appealing smell was the greatest influencer of consumer preference, while color and appealing smell were the best indicators of natural soaps’ estimated pricing and consumers’ perceived quality, and consequently acceptability."

In spite of all the scientific flowey-ness of the report, their conclusions were pretty obvious to me; conclusions already made in so many consumer goods, especially in health and beauty products. I chuckle a bit at hard they they tried to make conclusions sound so weighty. It would have been less impressive for the authors to write, "People most like the soaps that smell nice and look pretty."

Still, I found the discussion about the chemical interactions, saponification, antioxidants, additives, unsaturated and saturated fats, etc. most enlightening. There are so many factors that can influence the outcome of each and every soap recipe, making soap almost seems like magic!