Stearic Acid-when an ingredient just ain't so.

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Johnez

What if I....
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I'll preface this thread by stating I've learned a lot in this little journey. Biggest lesson is you cannot trust soap calcs to always be right. This stearic example is one of a few I have personally dealt with, however there are some other fats that are problematic. Second lesson is you cannot trust hearsay or popular belief. For some time I operated under the wrong information. This thread is mainly to make it utterly clear to everyone. Many already know the info in this thread, but know some here do not, and some who come in the future may not have that knowledge either-so this thread is for them. Unfortunately, this thread will probably die and we'll have to keep bringin up that stearic acid numbers are wrong in soap calcs and to factor that in...just like ResolvableOwl did for me long ago. However, I hope it sticks around in the greater group memory. Anyway, here goes nothin:

Every single soap calc is wrong when it comes to listing "stearic acid" and it's fatty acid composition. Nowhere can "Stearic Acid" be found with a Stearic Acid fatty acid content of "99%." None.

Soy wax is not fully hydrogenated soybean oil, and therefore does not have 87% stearic acid.

Every single soap supplier carrying stearic acid is selling a product that is a 50/50 mix of stearic acid and palmitic acid. Not a single soap supplier carries anything close to pure stearic acid (ie-not a product that is half palmitic acid).

I have tried over the course of the past few weeks to find a single solitary source of pure stearic acid. My search was fruitless so I modified the requirement that the final ingredient has to be a majority stearic acid, henceforth referred to as SA. Anyway, something in the range of 80-90% would have been ideal, heck I would have been satisfied with anything that shows a majority SA over PA. However it simply does not exist. Every single COA or document that lists the breakdown of fatty acids shows a roughly even distribution b/w SA and PA.

I have emailed promising suppliers. Soap suppliers and lab suppliers. I have pored through COAs and other documentation. Many soap companies are forthcoming and perfectly list their FA makeups, others do not. I don't begrudge any of them, as this seems to be industry practice. Some soapers have made the assumption that what is listed as "pure stearic acid" is in fact made up of 100% stearic acid in it's fatty acid profile, however that is not an assumption that satisfies my curiosity without an attached document that shows the explicit fatty acid composition, specifically stearic acid and palmitic acid. "90% pure," "100% stearic acid," "99% pure" are most likely referring to the purity of the substance, not the actual stearic acid content. If a final product that is "47% stearic acid, 47% palmitic acid, 1% myristic acid, 1% lauric acid" can be labeled as stearic acid, calling it 90% stearic acid means it's got 10% of random things like ash, water, other matter, etc. and is not referring to the SA fatty acid content.

If anyone is curious to take up the search, here's some further info:

CAS 57-11-4 is the unique chemical ID number for SA.

SA can be derived from palm, soy, beef tallow, rapeseed oil.

SA sources other than "Stearic Acid" include beef tallow, many butters (Shea, cocoa, mango, sal, and notably kokum). Butter sources generally have a very favorable SA : PA ratio, however generally are in the 40-50% range.

I did find exactly one study that some purport to have used pure SA. Sigma Aldrich W303518 is that product, however I've not seen any documents showing a clear fatty acid break down. What's interesting is the paper using the stuff in a diet study was specifically designed to test stearic acid fatty acid. It is promising, however the prices on the stuff are pretty outrageous.

Fully hydrogenated soybean oil may very well be a source of high stearic acid content. I've yet to find a source however. Soy wax is not fully hydrogenated soy wax however, and unfortunately is not 87% stearic acid as @Mobjack Bay has demonstrated in her threads (search it). If you happen to find a soy wax that isn't GW 415 or any of the common ones out there right now, check the iodine value. If it's anything near 0 it very well may have a super high stearic content.

So why does it matter? I started this search when reading things like SA is less soluble in water than PA. SA is more stable. SA is harder to lather. And more. Clearly some people feel there's a difference, so I set out to see if it could be demonstrates through isolation experiments. More importantly though is accuracy in our hobby, and for some our business. SAP values and FA content we assume to be true but are not can affect our final product. Worse it can cause us to make *other* faulty assumptions. I think this wrong info has persisted for too long, and though correct info has been passed along by many and often here, I think it's worthwhile to dedicate a thread to this issue.

Some docs and stuff:
Hydrogenated soybean oil
https://www.researchgate.net/public...rtening_Oils_via_Hydrogenation_of_Soybean_Oil
 

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It doesn't specify, but here are the clues that indicate it is not pure SA fatty acids:

"C16-C18 98%" refers to the carbon chains, stearic has 18, palmitic has 16. It appears this stuff is 98% palmitic and stearic acids.

Also, listed in synonyms in that document is "stearic- palmitic acid mixture."

At least it looks to be palm free still. :)
 
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Thank you. I have wondered if this may be the reason my syndet shampoo bars last year were such a total and utter failure. The process went beautifully (although messy at the start), but the resulting bars are an utter disaster in my hair, yet the recipe is one that is reputable and well loved by thousands.
 
Thank you. I have wondered if this may be the reason my syndet shampoo bars last year were such a total and utter failure. The process went beautifully (although messy at the start), but the resulting bars are an utter disaster in my hair, yet the recipe is one that is reputable and well loved by thousands.

The good thing is that when a recipe calls for stearic acid I don't think there's any way for anyone to get 100% stearic acid, so they are probably all using something similar.

A problem IMO is that "stearic acid" SAP values across different types (soy, palm, beef tallow, rapeseed oil) or methods might be different and causing issues. Most SA hover between 209 and 211 in SAP values. I have seen one (listed as "palm free") at 197. If you have access to a COA or if they list a SAP value you can get a more accurate amount of lye to use.

It might be a good idea to experiment a bit with variables like superfat, know your sources, and be aware this isn't an exact science.
 
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A problem IMO is that "stearic acid" SAP values across different types (soy, palm, beef tallow, rapeseed oil) or methods might be different and causing issues.
That could be a problem for those of us who use lower SF, like my typical 2%. However, I don't use SA in any of my soaps except shave soap, and I superfat those at a higher rate, so I'm probably safe. Still, it's good to be aware of the issue. Appreciate the sharing of your knowledge on this, @Johnez.
 
https://www.chempoint.com/products/...s/pmc-stearic-acid/hystrene-9718-nf-fg-powder
These guys sell various forms of stearic acid, specifically Hystrene 9718 which is 92% of actual stearic acid. Unfortunately they only sell 100 lb drums of this stuff lol.

However! There is a subreddit dedicated to saturated fat. Users in the sub are well versed in stearic acid and these guys love it for it's purported weight loss affects. Due to the "banana milk shake study" one company has decided to capitalize on the stuff and is selling Hystrene 9718 in little sacks for a decent price. Confirmed by the business owner, finally a source of stearic acid for the little guy:

https://fire-in-a-bottle.myshopify....oducts/stearic-acid-food-grade-90-purity-1-lb
 
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