Soap Spoilage

[Dean]

If a bar is comprised of various oils with the oil with the shortest shelf life being 1 year, can it be expected that the bar will go rancid/DOS after one year without preservatives? Does HP, CP or super-fat make a difference?

 

[amd]

Short answer: If your oils are well within their shelf life and the soap is well made, it should never go bad.

 

[DeeAnna]

I wouldn't automatically assume the soap WILL go rancid in a year. Or even the fat itself. The soap or the fat might go rancid, or it might not. Shelf lives are guidelines, not absolutes.

Soap can and does oxidize and turn rancid even with a very low superfat, but in my opinion, higher superfat increases the chances. Kevin Dunn did experiments that showed most soap tends to darken over time. He used this change in color as an indicator that the soap is oxidizing and is thus more likely to become rancid. His results showed less color change with lower superfat, however.

You can reduce the chance of oxidation and rancidity by using a chelator and/or an antioxidant. Pairing the two works the best, again according to Dunn's experiments.

You can also reduce the chances by storing your fats and soap in a cool, dark, and (for soap) low humidity place. Light (UV), moisture, and warmth accelerate the oxidation process that leads to rancidity. See Soapsmith's experiment on the effects of storage conditions on soap: http://soapsmith.blogspot.com/2015/09/soapsmith-dos-experiment.html

 

[Dean]

I wouldn't automatically assume the soap WILL go rancid in a year. Or even the fat itself. The soap or the fat might go rancid, or it might not. Shelf lives are guidelines, not absolutes.

Soap can and does oxidize and turn rancid even with a very low superfat, but in my opinion, higher superfat increases the chances. Kevin Dunn did experiments that showed most soap tends to darken over time. He used this change in color as an indicator that the soap is oxidizing and is thus more likely to become rancid. His results showed less color change with lower superfat, however.

You can reduce the chance of oxidation and rancidity by using a chelator and/or an antioxidant. Pairing the two works the best, again according to Dunn's experiments.

You can also reduce the chances by storing your fats and soap in a cool, dark, and (for soap) low humidity place. Light (UV), moisture, and warmth accelerate the oxidation process that leads to rancidity. See Soapsmith's experiment on the effects of storage conditions on soap: http://soapsmith.blogspot.com/2015/09/soapsmith-dos-experiment.html

Thanks for sharing the article. Its pretty clear that soap will spoil relatively soon w/o preservatives.

 

[DeeAnna]

"...soap will spoil relatively soon w/o preservatives..."

I disagree that this is an accurate interpretation of Soapsmith's tests. She had two findings -- one is that proper storage will minimize problems with shelf life. The second is the one you're focusing on -- that an antioxidant and/or chelant will further extend the shelf life. (The correct terminology here is not "preservative", by the way.)

IMO, there are two parts to making soap with the longest possible shelf life -- prevention and correction. Proper handling and storage is the prevention part -- this makes it less likely that problems will happen. Chelators and antioxidants are the corrective part -- solving any problems when they do occur.

We do the same about catching a cold or the flu -- firstly, good hygiene to avoid catching the disease and secondly, ways to treat the illness when it happens.

 

[Dean]

"...soap will spoil relatively soon w/o preservatives..."

I disagree that this is an accurate interpretation of Soapsmith's tests. She had two findings -- one is that proper storage will minimize problems with shelf life. The second is the one you're focusing on -- that an antioxidant and/or chelant will further extend the shelf life. (The correct terminology here is not "preservative", by the way.)

IMO, there are two parts to making soap with the longest possible shelf life -- prevention and correction. Proper handling and storage is the prevention part -- this makes it less likely that problems will happen. Chelators and antioxidants are the corrective part -- solving any problems when they do occur.

We do the same about catching a cold or the flu -- firstly, good hygiene to avoid catching the disease and secondly, ways to treat the illness when it happens.

Thanks for the correction.

 

[cmzaha]

Last week I found a soap made in 2014 which smells perfect, and not rancid, no dos spots. The fo is Big Sur and contains 0.01% Bht and Tetrasodium EDTA @0.5%

 

[shunt2011]

I have a couple from 2012 and other than the fo fading they are still great soaps. Nothing special added. Olive, Palm, CO, Shea and Castor.

 

[DeeAnna]

I keep a "bone pile" of samples of soap I've made, the older ones without any chelator/antioxidant and the younger ones with. The oldest ones date to the time when I started soaping in 2012.

The idea that the shelf life of soap is determined by the shelf life of the oils doesn't seem to directly apply to the soap I make. Some of the reasons why I make the soap I do are based on the idea of avoiding rancidity, so maybe that's why I don't see a correlation. I don't make soap with a large percentage of linoleic and linolenic acids. I also don't make soap with high superfat, except for a batch or two early on in my soaping misadventures.

Some of my pre-EDTA soap samples (these would be three or more years old) show DOS (spots of rancidity) but others do not. The unpredictable nature of DOS supports my opinion that spots of rancidity relate to random bits of contaminants within the soap batter. I do my best to prevent any extra bits from contaminating my soap, and I now use ROE and EDTA to clean up the bits I cannot prevent.

I have been able to link overall rancidity (where the soap turns orange all over and has a definite smell) to using old EOs in a high superfat soap. Thankfully this has only happened once, but the experience was a eye-opener.

 

[Serene]

DeeAnna,

I have a question regarding ROE. Other than the suggested use by date, does ROE have a shelf life? Looked at your write up and did not see anything along with some other web searches. Sorry if this derails the topic. Did not want to start a new one.

Had to edit hoping to clarify since after I read what I asked it sounded stupid.
So for example: Jojoba oil has a long shelf life of about 5 years and in some cases some websites give it more, yet when I purchased it the suggestion is to use it within a year. So I have ROE that I purchased 2 years ago and I still have less than half left. Should I get rid of it and re purchase?

Thank you in advance.

 

[DeeAnna]

I don't know if manufacturers and distributors set a shelf life for ROE. The oleoresins and absolutes tend to have a longer shelf life than EOs, but even rosemary EO should be good for at least 2-3 years, according to my notes. It's my opinion that the oleoresin should be good for at least that long.

I buy only a small amount of ROE at a time, mark the date of purchase on the container, keep it in the fridge, and try to use it up within a few years.

 

[Serene]

Thank you, DeeAnna.

 

[Dean]

I keep a "bone pile" of samples of soap I've made, the older ones without any chelator/antioxidant and the younger ones with. The oldest ones date to the time when I started soaping in 2012.

The idea that the shelf life of soap determines the shelf life of the oils used doesn't seem to directly apply to the soap I make. Some of the reasons why I make the soap I do are based on the idea of avoiding rancidity, so maybe that's why I don't see a correlation. I don't make soap with a large percentage of linoleic and linolenic acids. I also don't make soap with high superfat, except for a batch or two early on in my soaping misadventures.

Some of my pre-EDTA soap samples (these would be three or more years old) show DOS (spots of rancidity) but others do not. The unpredictable nature of DOS supports my opinion that spots of rancidity relate to random bits of contaminants within the soap batter. I do my best to prevent any extra bits from contaminating my soap, and I now use ROE and EDTA to clean up the bits I cannot prevent.

I have been able to link overall rancidity (where the soap turns orange all over and has a definite smell) to using old EOs in a high superfat soap. Thankfully this has only happened once, but the experience was a eye-opener.

Hi DeeAnna.

How high linoleic is problematic? I’m trying a new 19% linoleic recipie today. Read that linoleic has an emollient quality thats different than oleic.

 

[DeeAnna]

The rule of thumb that many people use is to keep the combined linolenic and linoleic acids under 15%. I don't know of any scientific studies that support or disprove this rule of thumb, however. Most of my recipes are in the 5 to 10% range.

I'm not sure if you're making this assumption or not, but I'll say this to cover all bases -- Don't confuse the properties of certain oils with the properties of soap made from those oils. Emollience is the property of being able to soften or smooth the skin. Soap can be a mild cleanser that does little to disturb the skin's natural fats and proteins. Or it can be a strong cleanser that can dry or irritate the skin. But I think it's a real stretch to assume soap has emollient properties. I'll stick with my lotion for that.

 

[Dean]

The rule of thumb that many people use is to keep the combined linolenic and linoleic acids under 15%. I don't know of any scientific studies that support or disprove this rule of thumb, however. Most of my recipes are in the 5 to 10% range.

I'm not sure if you're making this assumption or not, but I'll say this to cover all bases -- Don't confuse the properties of certain oils with the properties of soap made from those oils. Emollience is the property of being able to soften or smooth the skin. Soap can be a mild cleanser that does little to disturb the skin's natural fats and proteins. Or it can be a strong cleanser that can dry or irritate the skin. But I think it's a real stretch to assume soap has emollient properties. I'll stick with my lotion for that.

Thanks DeeAnna.

I love how soaping has so many variables. Just when I think I figured it out, I discover a new twist or nuance. I think Ill forgo the high linoleic safflower in my recipe use mostly almond for the soft oil. Almond oil got a great review in the single oil lather test.

 

[DeeAnna]

Welcome to the club, Dean! I'm looking forward to hearing the results of your soapy adventures, with all the nuances and plot twists.

 

[OrganicSoapGuy]

The rule of thumb that many people use is to keep the combined linolenic and linoleic acids under 15%. I don't know of any scientific studies that support or disprove this rule of thumb, however. Most of my recipes are in the 5 to 10% range.

DeeAnna, thanks for naming this. I'm a newb here at the forum, but concur with your rule of thumb based on a fair bit of experience. I just responded to another post on the same topic that discusses the Kevin Dunn article (https://www.soapmakingforum.com/thr...ioxidants-and-chelating-agents-in-soap.69814/)

We've found the two strongest correlations to DOS are 1) levels of poly-unsaturated FA's (such as linoleic) and 2) temp levels (such as when melting the oils). Poly-unsaturated FA's are highly susceptible to oxidation due to their multiple double bonds. Then, if you add too much heat during any of the processes, the heat will provide the energy needed to open up double bonds, effectively priming the pump for oxidation. Of these, the easiest solution is to formulate in a way that minimizes the poly-unsaturated FA's.

Superfatting level, by itself, is not a strong factor in DOS. However, superfatting with an oil like soy or non-HO sunflower, will be a problem. In other words, it comes back to the stability of the oils. And, if the oils are accidentally overheated before using them, or if there is too much heat in CPOP, those superfatted poly-unsaturated oils will want to turn to DOS's even more.

I think we sometimes focus too much on adding in substances to extend shelf life when, if recipes stick to your rule of thumb about low linoleic/linolenic levels, the need will be reduced.

 

[DeeAnna]

"...I think we sometimes focus too much on adding in substances to extend shelf life..."

Well, yes and no.

If you're talking about reducing the chance of overall oxidation and rancidity by limiting the linoleic and linolenic content, I believe you have a valid point.

If you're referring to spots of rancidity (aka DOS), then I'm not sure your point of view entirely applies. DOS is more related to discrete contaminants, especially metals, that trigger oxidation and rancidity in the area around the contaminant. Even a soap made entirely with saturated fatty acids isn't immune to this problem. Soap makers can't entirely prevent this kind of contamination, which is why chelators and antioxidants are useful.

 

[SoapAddict415]

This is all so interesting. I never even considered the fact that bar soap could spoil. I always thought that most soap, if properly stored, would keep forever.

 

[DeeAnna]

Soap can go bad or not, depending on a fair number of variables. Here's a neat experiment done by Soapsmith that shows how storage methods can affect the shelf life of soap -- http://soapsmith.blogspot.com/2015/09/soapsmith-dos-experiment.html

We can do a LOT to reduce the chance of spoilage by proper handling and storage of soap and soaping ingredients as well as making smart choices of those ingredients. Antioxidants and chelators are valuable (but optional) tools to also consider using.