Can soap salts go rancid?

Soapmaking Forum - Soap & Candle Forums

Help Support Soapmaking Forum - Soap & Candle Forums:

LisaBoBisa

Well-Known Member
Joined
Jan 12, 2022
Messages
123
Reaction score
270
Location
US
Chemistry experts, please forgive any wrong wording. 😅
After 2 batches that shouldn't develop DOS did in my humid apartment, I've fixed the humidity, but I'm also second-guessing my understanding of DOS, HP, and rancidity in soap.

Can soap salts go rancid? Is it only the superfat that potentially causes DOS?

So oils and fatty acids cause DOS when they go rancid. (@DeeAnna Thanks so much for this resource). For the last year, I figured that meant soap salts are safe... that the oils that get saponified are locked down, safe from oxidation, and I only need to worry about my superfat oxidizing. But a soap salt is a sodium ion and a fatty acid ion. Does that mean the fatty acid ion in a soap salt can go rancid and cause DOS? Which means a 0% SF soap could get DOS even in a perfect situation where there's no excess oil?

If not, my new bottle of lavender EO from BB might be bad, but I've always gotten great products from them...
 

LisaBoBisa

Well-Known Member
Joined
Jan 12, 2022
Messages
123
Reaction score
270
Location
US
As I understand the chemistry, the fatty acid molecule that ends up attached to the sodium is pretty much unchanged during soap making and can develop DOS.
Thank you! Welp... I need to go back and reformulate my HP recipes with lower linoleic/linolenic acid %, then!

Here's the weird thing: I decided to learn HP after reading this article and the Q/A thread that follows. Sounds like there's an old depression era tradition of making 0% SF soap with household oils that go rancid. My second batch of HP was made with a mixture of fresh and rancid oils before the cook, and a nice, fresh, stable butter after the cook for the superfat. No lingering smell, (also not much scent from the EOs, either, since I was a noob and added them when the soap was too hot). I used this and shared a few bars with a friend; ended up being my favorite batch. Still no DOS a year later on the bar my friend hasn't used. I have no idea why that seemed to work so well, or why other folks mention their mothers and grandmothers doing this, if the fatty acids are still oxidized. But it also makes sense; why would the oxygen attached to the fatty acid disappear, just because the fatty acid is now attached to a sodium ion instead of covalently bonded to a glycerol molecule?
 
Last edited:

earlene

Grandmother & Soaper
Supporting Member
Joined
Apr 30, 2016
Messages
9,632
Reaction score
11,718
Location
Western Illinois, USA
I had the opposite experience using rancid oils in soap. I 'washed' the rancid oils and was not successful in removing rancidity. I salted out rancid soap and was not successful in removing the rancid odor of the soap. Hours and hours and hours, unknown gallons of water, plus unknown KiloWhatt Hours of electricity used up in those processes. All of which eventually got tossed into the trash because the rancid odors were simply unbearable to my nose. So even though some folks have reported it works for them, there is no guarantee that it will always work in all cases.

Incidentally, lavender EO is notorious for contributing to DOS in soap. I love it myself (not the DOS, but the lavender), but I always keep that in mind when I add it to one of my soaps. I believe it is better added to a recipe low in unsaturated fats thereby giving it less to work with in terms of oxidizing.

Another point I'd like to make is that unless a soapmaker truly knows the actual purity of the lye used at the time the soap is made (by testing it accurately), AND truly knows the actual SAP value of every ingredient in the soap formula used with that lye that day, there is no real guarantee that even if the goal is a 0% SF soap, that that is what the soapmaker will get.
 
Joined
Apr 19, 2019
Messages
4,100
Reaction score
9,722
Location
Virginia
The water issue is exactly why I don’t do a lot of salting out of soap. I tried salting out using water from the dehumidifier last year and it’s fine a year later, but I would not give the soap away to anyone.

I have never had any issues with lavender (or lavandin) EO, perhaps because I buy it from a good supplier, keep it stored in the refrigerator and use it up fairly quickly. I have soaps with lavender EO that are over two years old, including a 95% OO batch, and they’re fine.
 

LisaBoBisa

Well-Known Member
Joined
Jan 12, 2022
Messages
123
Reaction score
270
Location
US
Thank you all so much... Really grateful for your help.
@earlene I appreciate your cautions; I probably won't bother with washing rancid oils, just to be safe!

The last two months have knocked the wind out of me a little as a soaper... I was just beginning to masterbatch, made my first 4-lb batch of soap, but started noticing certain batches develop DOS one by one, starting during our record-breaking May temps (never had this happen before). As of this week, I've lost 12 lbs of soap, but thankfully noticed the trend before I sold the batches.

The main trigger: a hot, humid apartment, but it seems like only the batches with oxidation helpers developed DOS (colorants like dandelion or spirulina that are high in copper, unsaturated fatty acids close to 15% or higher, coconut milk with guar gum, ZNC Soleseife made with iodized salt but fresh olive oil).

Any of these things on their own never caused problems for me in a cool apartment, but add humid heat...

I got my wonderful new 35-pint dehumidifier June 11, and began using my AC round the clock like a normal person two days before that (I like heat, so I don't normally crank it, but soap needs AC), but I've also done a fearless and searching DOS cause inventory.

New plan:
1. Dehydrator runs all the time in my curing area now. It takes over a day to fill its tank now, so I know it's less humid inside (took 14 hours to fill at first). AC stays on constantly, but not too low (I don't like cold)
2. No more copper-rich colorants like dandelion or spirulina. Cucumber has a lot less copper per 100g, so I've dehydrated cuke peels to try when I know the problem's definitely under control
3. No more fragile oils unless I have room for them in the fridge, and even then keep 'em at 5% or less (2% for rosehip). Soy looks unglamorous on an ingredient list anyway.
4. I maybe won't trust my Vinevida French lavender; it's lived in the fridge since I bought it in November, but the bottle has been half full since March, so there's air in the bottle. A lavender batch I made with it was the first to develop DOS in May, but that batch also had over 15% polyunsaturated fatty acids, guar gum, and the heat/humidity problem to explain its DOS. I'll probably use it for something other than soap to be safe.

SO... this has been an expensive lesson, and I've avoided mixing up new batches for the last 5+ weeks while I troubleshoot the heck out of this and reformulate my HP recipes. I've made test soaps of individual oils to make sure my solid oils etc are safe, and that I didn't buy my new olive oil in bad shape (hot summer, and I've lost too much to take chances).

But I'm so glad I learned all this before selling this summer! My curing area has been dry and cool for 5 weeks+, plenty of my soap wasnt affected (different recipes, less polyunsaturated fats, no ingredients that promote oxidation).

Welp... time to get back on the horse! A friend's dad has been asking for beard soap, and I know that recipe is safe!
 
Last edited:

DeeAnna

Well-Known Member
Joined
Feb 20, 2013
Messages
14,104
Reaction score
21,354
Location
USA
...So oils and fatty acids cause DOS when they go rancid. (@DeeAnna Thanks so much for this resource). For the last year, I figured that meant soap salts are safe... that the oils that get saponified are locked down, safe from oxidation...

Oy. That's not how I intended the info in my article to be interpreted. I need to rewrite this.

Fats contains fatty acids. The fatty acids in fat molecules can go rancid.
Soap contains fatty acids. The fatty acids in soap molecules can go rancid.
Free fatty acids can go rancid too.

They ALL contain fatty acids, thus they ALL can oxidize and go rancid.
 

LisaBoBisa

Well-Known Member
Joined
Jan 12, 2022
Messages
123
Reaction score
270
Location
US
Oy. That's not how I intended the info in my article to be interpreted. I need to rewrite this.
@DeeAnna I didn't get that idea by reading your article--your article helped me start questioning my wrong ideas and find some copper-rich ingredients to avoid, actually!
After looking up the USDA info, dandelion greens are even more copper-rich than spirulina, so they could go on the list. I've read that rose clay is copper-rich, but not sure how rich, and it seems like a lot of people have been using it for decades without problem.

This is actually where I got the wrong idea.
 
Last edited:

DeeAnna

Well-Known Member
Joined
Feb 20, 2013
Messages
14,104
Reaction score
21,354
Location
USA
Whew! Thanks for explaining, @LisaBoBisa. I'll not break out my red pen to edit just yet.

I had read the "Don't throw out that rancid oil! Make soap!" article a long time ago and found it interesting, but I thought the author glossed over the problem of odor.

I first thought they were using only slightly rancid fat with minimal "off" odor, but after reading more, I don't think that was the case. I really wondered why the author was okay with this idea. What others say and what I've experienced is that a rancid smell is difficult to disguise with scent -- the odor lingers on your skin after washing.

I've done a few "kitchen chemistry" tests with rancid fats and think washing rancid fat can make it smell somewhat better (but it's not a 100% perfect solution). I don't think it's worth the trouble to use rancid fats for soap making without washing them first to reduce the odor.

Soap making manuals from the 1800s and early 1900s often have long sections devoted to deodorizing and bleaching low-quality or rancid fat for use in soap making, so it's not just me acting like a prima donna. It's an issue soap makers have dealt with for a long time.

As far as the sodium ion "protecting" the fatty acid of the soap molecule, it's possible this may have a slight protective effect, but I don't see it as a surefire solution to prevent rancidity in soap. I know the old soap makers often made slightly lye heavy soap with the idea of improving shelf life, but even so they treated soap as a commodity with a fairly short shelf life. Modern commercial soap makers use chelators and antioxidants (as well as low superfat) to lengthen the shelf life, and I think those additives are more reliable solutions.
 

LisaBoBisa

Well-Known Member
Joined
Jan 12, 2022
Messages
123
Reaction score
270
Location
US
Whew! Thanks for explaining, @LisaBoBisa. I'll not break out my red pen to edit just yet.

I had read the "Don't throw out that rancid oil! Make soap!" article a long time ago and found it interesting, but I thought the author glossed over the problem of odor.

I first thought they were using only slightly rancid fat with minimal "off" odor, but after reading more, I don't think that was the case. I really wondered why the author was okay with this idea. What others say and what I've experienced is that a rancid smell is difficult to disguise with scent -- the odor lingers on your skin after washing.

I've done a few "kitchen chemistry" tests with rancid fats and think washing rancid fat can make it smell somewhat better (but it's not a 100% perfect solution). I don't think it's worth the trouble to use rancid fats for soap making without washing them first to reduce the odor.

Soap making manuals from the 1800s and early 1900s often have long sections devoted to deodorizing and bleaching low-quality or rancid fat for use in soap making, so it's not just me acting like a prima donna. It's an issue soap makers have dealt with for a long time.

As far as the sodium ion "protecting" the fatty acid of the soap molecule, it's possible this may have a slight protective effect, but I don't see it as a surefire solution to prevent rancidity in soap. I know the old soap makers often made slightly lye heavy soap with the idea of improving shelf life, but even so they treated soap as a commodity with a fairly short shelf life. Modern commercial soap makers use chelators and antioxidants (as well as low superfat) to lengthen the shelf life, and I think those additives are more reliable solutions.
@DeeAnna OH my goodness--so glad you read that article, too. I HATE wasting stuff, and grew up in a Costco family... and people give me their old oils, so I loved the idea of being able to make something useful with this otherwise wasted oil. My 5th-8th batches as a noob were HP rancid oil soaps with fresh cocoa butter superfats, and oddly enough, they still looked and smelled pretty a year later (clove and (faded) orange EO in some, a little peppermint and tea tree in others). I've never tried washing rancid fat, not sure why the off smell almost completely vanished in those noob rancid oil soaps during the HP cook; maybe my oils weren't rancid enough? I wonder why those DIDN'T develop DOS?

Do you or anyone else have advice for cleaning my soap curing shelves after a batch developed DOS, so I don't "contaminate" future batches? (I've been using stackable cardboard strawberry flats rescued from Costco... maybe I should recycle them and grab new ones)
 
Last edited:
Top