Yellow spots appearing on soap

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Violet253

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I made a batch of soap about a month ago which is starting to develop yellow spots that are gradually growing larger. I feel quite baffled about what is causing it as I've used the same recipe over the last couple of years and this has only happened a couple of times. I'm thinking it may have come into contact with something during curing ?
 

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ResolvableOwl

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Hi @Violet253. Welcome to SMF! And welcome to rancid soap aka Dreaded Orange Spots (DOS). :(

Your observations and the photo are quite unambiguous, IMHO. DOS is an, umm, dreaded thing to happen to soaps. Well-known enough to have a terrifying name by itself. And when it occurs, it is too late already.
The soap is technically still usable, but the yellowing is unsightly, and at some point DOS starts to smell off. Nothing you would want to use any further, let alone give out of hand.

The discolouration is a complicated decomposition of poly-unsaturated fats that have come into the soap via the oils (“luxury oils” like hemp, safflower, but also sunflower, canola and lard are prone. Long storage is detrimental too). It is fostered by unfavourable storage (warm, moist, not in the dark), as well as minute (inevitable) contaminations with heavy metals, also from things like metal grids used for curing.
Read the above link that already contains a comprehensive overview, and includes strategies how to avoid DOS in the future (chelators, antioxidants).
 

Violet253

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Thank-you for your reply. The soap has already started to smell a bit off ! I didn't realise metals could affect soap - I used tin foil to cover a jar whilst infusing the oils with alkanet root so I'm wondering if this is how it happened. The soap has only been curing for around a month so it isn't very old. It's only appeared on two of the bars from the batch so far so I'm hoping it won't appear on any more!
 

ResolvableOwl

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I guess you mean aluminium foil? Aluminium likely isn't the worst in creating DOS, but still should be kept away from soapy stuff for many other reasons (eaten up by lye, etc.).
That young, it seems likely that one of your oils is already at or beyond its use-by date and/or was inappropriately stored (not necessarily your fault).

What does a soap calculator output as the content of linoleic acid of your recipe?
 

Violet253

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Yes it was aluminium foil. I stored the infused oil in jars with the foil covering it for a couple of days before using it, so it wasn't airtight, could this have made a difference?

The linoleic acid comes out as 8 - I've attached the formula I used. The only other ingredient I added in was the alkanet infusion.
 

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ResolvableOwl

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Oof. Covering a jar with oils with aluminium foil should be next to zero risk (it'd be something different it it had contact with lye or finished soap). That recipe actually looks quite resistant against DOS, no “notorious” ingredients. But on the other hand, it is not unheard of that olive oil behaves strangely – many have zero issues, but quite some get DOS after a few months (though one month really isn't a long time, at the more with this low linoleic content).
Things you could try in the future: Lower superfat (5% is plenty, and 2-3% would still give a luxurious skin feel, if you are comfortable with lye weighing precision). If you used extra virgin OO, you could swap it with refined OO, pomace OO or even high-oleic sunflower/safflower, which are anecdotally less prone to DOS. And in general avoid oldish batches (including NaOH – though this is not a direct DOS risk, NaOH pulling water and CO₂ makes your lye measurement imprecise).
 

Misschief

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Wait....
The only other ingredient I added in was the alkanet infusion.
Alkanet is used to colour soap...... yellow.

How was your soap stored? What fragrance did you add? It does look like DOS but that recipe is very similar to one of mine and my bars still don't have DOS, even after a year or more.
 

Violet253

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I didn't use any fragrances, the alkanet was the only additive. I store the soap spaced out on coated cooling racks. I've been reading through the link resolvableowl sent and noticed it recommended distilled water rather than tap water - I've been using tap water so I'm wondering if maybe that could have caused it ?
 

ResolvableOwl

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Ahh, yes, that might well be the case. Tap water doesn't do well with soapmaking for several reasons. There is a good chance that trace metals present in tap water and/or dissolving from plumbing, that are harmless for human consumption, but can hurt unsaturated fats in the long run.
Chelators can scavenge these to interfere less with the soap molecules.

Quick fix is as easy as adding citric acid/sodium citrate (or replacing some of the water with lemon juice). And of course use distilled water (rain water, molten snow, aloe vera juice…) instead of tap water.
 

DeeAnna

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"...The discolouration is a complicated decomposition of poly-unsaturated fats that have come into the soap via the oils ..."

Although polyunsaturated fats are more likely to oxidize sooner than monounsaturated and saturated fats, even saturated fats will eventually oxidize and go rancid.

Oxidation and rancidity are part of the natural cycle of decomposition. No fat, being a product of nature, is immune to decomposition.
 

dibbles

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One other thought - even though your racks are coated, you might try putting a clean cotton tea towel or parchment between the rack and the soap. I use plastic mesh embroidery canvas like this, which can be found at most craft stores.
 

Misschief

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Ahh, yes, that might well be the case. Tap water doesn't do well with soapmaking for several reasons. There is a good chance that trace metals present in tap water and/or dissolving from plumbing, that are harmless for human consumption, but can hurt unsaturated fats in the long run.
Chelators can scavenge these to interfere less with the soap molecules.

Quick fix is as easy as adding citric acid/sodium citrate (or replacing some of the water with lemon juice). And of course use distilled water (rain water, molten snow, aloe vera juice…) instead of tap water.
Not necessarily true. I have used tap water for years with no issues whatsoever. It would depend more on your location. We have soft water in our area; others have hard water. It would have more to do with the mineral content of your water.
 

ResolvableOwl

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Yes, that's my point. It is not necessarily true that tap water is unsuitable for soapmaking. You can't rely on tap water to be well-behaved. If it does, fine. But since the mineral content of tap water depends on things like how the waterworks blend their supplies and what they put in for clarification and sanitation, or how long you have let the tap run in advance, reliability is a matter of luck. Of course everyone can decide for themselves if they want to rely on luck for troubleshooting DOS, but I wouldn't recommend it.
 

ResolvableOwl

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Although polyunsaturated fats are more likely to oxidize sooner than monounsaturated and saturated fats, even saturated fats will eventually oxidize and go rancid.

Oxidation and rancidity are part of the natural cycle of decomposition. No fat, being a product of nature, is immune to decomposition.
That statement sounds very pessimistic. If correct and relevant, this would have quite drastic consequences for soapmaking as a whole!
I cannot understand how such a generalising assertion is meant to support a new member, who has actually come here in hope to gain advice, not nihilism. Unless some scientific grounding, context and clarification of practical limits are provided, comments like this are not helpful.
 

earlene

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That statement sounds very pessimistic. If correct and relevant, this would have quite drastic consequences for soapmaking as a whole!
I cannot understand how such a generalising assertion is meant to support a new member, who has actually come here in hope to gain advice, not nihilism. Unless some scientific grounding, context and clarification of practical limits are provided, comments like this are not helpful.
Seriously? Come on. It's like death and taxes. Left to exposure, it's gonna happen, be it a living organism, or by-products of formerly living organic matter such as oils. Do you really believe that a scientific reference needs to accompany a statement that reiterates that decomposition is inevitable? Some things may take longer to decompose, like steel for example, but given time and the right conditions even steel will decompose.


Yes it was aluminium foil. I stored the infused oil in jars with the foil covering it for a couple of days before using it, so it wasn't airtight, could this have made a difference?
I would be more concerned about how fresh your oils were to start with, than the use of aluminium foil on the top of the jar in which you made your infusion. Oils have a limited shelf life before they start to go bad (oxidation, rancidity, etc), although it varies with different types of oils. If you start out with oil past its shelf date, it's more likely to contribute to DOS (dreaded orange spots) or rancidity than fresh oils. Adding other factors to older oils will just speed up the process.

We do have fairly hard water so maybe that was the issue.
Some minerals in water are more likely than others to contribute to DOS. But so do various other factors, like contaminants from handling (our bare hands, for example, work surfaces not thoroughly cleaned could also be a factor, impure additives is another possibility.)

And another factor can be super-fat. Your recipe is set at 5% super-fat, which means the goal with that recipe is that 5% of the oils do NOT get saponified. The excess fat that does not saponify remains free to go rancid when the right conditions exist. Even while using a soap calculator, there is potential for a higher super-fat than we plan. That can happen when we accidentally put a bit more oil into the mix than called for, either by human error or equipment malfunction (the weighing scale). It can also happen if our lye has absorbed water from the air (particularly when leaving a bottle of lye open to a humid room for any length of time); then when weighing the lye, we are actually weighing lye+water (absorbed from the air.) Also the Saponification values of oils are generally a range (xxx-xxx) rather than an exact number for that specific batch of oil, so variations can occur. All these things can contribute to a higher super-fat, and if the oil is already old, that can contribute to DOS.

This does not mean that rancidity is inevitable in all soap, but excess fat will very likely go rancid eventually if the soap remains on the shelf for years and years and sometimes sooner.
 
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