Linal=Dossy?

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Millie

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The batch of lavender soap that brought me to the forum :) is starting to smell off. No DOS yet but it's on its way! DeeAnna has mentioned in a few threads that lavender EO is prone to DOS. I'm wondering if linalool and linalyl acetate (interaction with NaOH produces linalool) are the culprets? If so what limits should I set in my scent formulations? Bergamot oil comes to mind... I found a spot of DOS on a neglected year+ bar of 100% bergamot (roughly 30% linalyl acetate). No hint of bergamot scent on that bar, just a bit of "off" scent. I have a bar left of a blend with bergamot at 20% (6% linalyl acetate) around 20 months old - the scent has changed, bergamot seems to fade quickly like other citrus oils, but it doesn't smell distinctly musty (although cedar and patchouli might mask some mustiness). Any thoughts?

ETA: I'll have to look up how much scent was added to each soap, but my personal max for EOs is 1 oz ppo. My guess is the bergamot blend was around 0.7 oz ppo.
 
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If the problem with lavender EO is caused by the reaction with the alkali, then all lavender would cause rancidity/DOS. But that's not what happens. As time passes, lavender EO oxidizes -- reacts with oxygen -- and the chemical change that results from the oxidation is the culprit.

And remember -- DOS (dreaded orange SPOTS) are not what I'm talking about here. SPOTS of rancidity usually come from discrete particles of contamination, such as metal fragments, dirt particles, powdered additives, etc.

Lavender EO in soap is distributed throughout the soap. Rancidity from Lavender EO will be an overall change. The whole bar will turn various shades of orange and will smell musty/off.

So if you have DOS, look for particles of contamination.
If you have overall rancidity, look for an ingredient that is evenly mixed throughout.

***

PS: The writer in the thread you mentioned, Lenarenee, has some good points. I think what you're sharing here is mainly his suggestion to keep a newly-made soap tightly covered for a few days after making? His thought was this will help ensure the fats and fatty acids are saponified as much as possible. I understand his point but I question how important it is, given that the superfat in most people's soaps is usually fairly high.

Remember that the actual superfat is going to be approximately the desired superfat plus the % of impurities in the NaOH. Many people use 5% superfat and the NaOH impurities run 3% to 10%, so a lot of soap has 8% to 15% actual superfat. I don't think slowing down the initial drying process to ensure full saponification for soap like this will make a big difference in reducing the chance of rancidity.

Just my opinion, however.
 
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So the spot of DOS in the bergamot soap is unrelated. I think it was musty all over, which would be something spread throughout, but I don't have it any longer to confirm. So - it could be both, or just the former. Hmm...

I was wondering if any chemical components in lavender EO that are prone to oxidation had been pinpointed. Because linalyl acetate and linalool are so high in lavender oils I was thinking they might be something to limit, the way soapers try to limit certain fatty acids in base oils.

I might be asking a question that is over my head....
 
I'm not sure you can limit linalyl acetate and linalool if you actually want lavender EO. They're the key chemical components of lavender.

"...linalyl acetate, a major constituent of lavender oil, can oxidize in the presence of atmospheric oxygen, “forming allergens that can cause contact dermatitis” (Sköld et al 2008 ). Indeed it can, as can linalool, the other major constituent of lavender oil (Sköld et al 2004 ). However, these are theoretical risks, not actual risks, and lavender oil oxidation is a process that takes many months, even years. What this research suggests is that products containing lavender oil should be protected from oxidation by the addition of antioxidants, and that very old products should be discarded. The International Fragrance Association (IFRA) does not have a regulation for lavender oil, but it does for linalool. Referring to linalool-rich essential oils, the IFRA guideline recommends the addition of an antioxidant: “The addition of 0.1% BHT or a-tocopherol has shown great efficiency” (IFRA 2009)...." http://roberttisserand.com/2011/12/lavender-oil-and-negative-innuendo/

"...To be super-safe, use undiluted lavender oil within 12 months of purchase, keep it cool and away from strong sunlight, and add an antioxidant to any product containing it (not needed in soaps)...." http://roberttisserand.com/2011/08/lavender-oil-skin-savior-or-skin-irritant/

Also see: http://www.usingeossafely.com/shelf-life-of-essential-oils-and-how-to-make-them-last-longer/

The last article suggests a 4 year shelf life for lavender EO. Tisserand suggests a more conservative 1 year period in the above "skin savior" article. You'll have to use your own good judgement about what makes sense for you and your soap. Regardless of what you think is the better answer, using refrigeration, excluding light, and minimizing the head (air) space in the bottle will be important.

Also, these references are talking about the use of lavender on skin, not about minimizing the chance of rancidity in soap, so that's a point to keep in mind. But maybe the info will offer some perspective.
 
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My over 2 year-old-lavender bars have no DOS, so I don't actually believe that Lavender EO always contributes to DOS. I love these bars and it's my very favorite recipe so far for the feel it gives my skin. I have since made the same recipe leaving out the SL (originally I used SL for ease of removal from the mold, but don't like SL quite so much anymore), different colorants and additional additives (originally I did not use ROE or EDTA, but now I do.) My first lavender soap had the default 3% that the online lye calculator suggested. I now add more than that with lavender EO, so it would be interesting to see if those bars develop DOS.

I wonder if the combination of soaping oils (and their respective fatty acid profiles) in combination with whatever fragrance and whatever other additives don't just ALL work together to inhibit or foster DOS development. It makes sense to me anyway.

Not that I claim to have created a DOS resistant recipe by any means. I've had my share of DOS in other soaps made around the same timeframe as soaps that have never developed DOS. I am positive that my inexperience at the time contributed to some of it, as well as using questionably old oils (I was new and didn't know any better). More like a happy accident that I have a recipe I created when I was new that my skin just absolutely adores and it hasn't DOS'd on me yet.

With a bit over 2 years of making lye soap under my belt, I feel that I am still in the newbie category with so much more to learn. It's not even funny how new I feel at times!
 
"...I don't actually believe that Lavender EO always contributes to DOS..."

And neither do I. I want, once again, to be perfectly clear about this -- it's OXIDIZED lavender EO that is the culprit. If you don't have oxidized lavender EO, then the EO will not trigger rancidity.

I'm being emphatic about this, because I don't want to be the cause of one more weird soaping myth.
 

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