# Liquid Castile soap creating a vacuum. How?



## Karen jw (Jul 22, 2019)

This week I made my first liquid soap. I only used pure extra virgin olive oil (later found out extra Virgin is not the best choice if you want a clear soap but that's not important just now). It diluted nicely to a good thick liquid and I put it into a lemonade bottle. It was room temperature when I bottled it.
It seems to be creating a vacuum as the bottle is getting sucked inwards.
I equalised the pressure yesterday and it's done the same again today.
Can anyone explain what's causing this as I'm intrigued.


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## Zany_in_CO (Jul 22, 2019)

Weird. I'm intrigued too! I hope one of the science gurus drops in to explain what's going on.


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## Karen jw (Jul 22, 2019)

Zany_in_CO said:


> Weird. I'm intrigued too! I hope one of the science gurus drops in to explain what's going on.
> View attachment 40484


Haha yes I'll post a pic in the morning as it's 2:30 am here in the UK and I don't want to disturb the family


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## Mobjack Bay (Jul 22, 2019)

Very interesting. Is the bottle totally filled with liquid soap, or is there an air space?


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## Karen jw (Jul 22, 2019)

Mobjack Bay said:


> Very interesting. Is the bottle totally filled with liquid soap, or is there an air space?


It's about two thirds full so a fair bit of air space.


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## Mobjack Bay (Jul 23, 2019)

I am by no measure a chemist, but I’m still willing to throw out some hypotheses!  It’s a puzzler for sure!  Based on what you’ve described, it doesn’t seem like a change in soap temperature, room temperature or ambient air pressure can explain what happened. You need a volume change inside the bottle due to some other process.  One thought I had is that the soap is pulling something out of the airspace that is “fitting” into the liquid soap without changing the volume of the soap fraction while the volume of the air decreases.  Alternatively, perhaps the volume of the liquid soap can decrease (density would increase) due to the molecules “packing” together with time.


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## HaniS (Jul 23, 2019)

Karen jw said:


> This week I made my first liquid soap. I only used pure extra virgin olive oil (later found out extra Virgin is not the best choice if you want a clear soap but that's not important just now). It diluted nicely to a good thick liquid and I put it into a lemonade bottle. It was room temperature when I bottled it.
> It seems to be creating a vacuum as the bottle is getting sucked inwards.
> I equalised the pressure yesterday and it's done the same again today.
> Can anyone explain what's causing this as I'm intrigued.



Carbon dioxide. The reaction still needs Oxygen and it's trying to absorb it from the outside.


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## Karen jw (Jul 23, 2019)

Mobjack Bay said:


> I am by no measure a chemist, but I’m still willing to throw out some hypotheses! ........ that the soap is pulling something out of the airspace that is “fitting” into the liquid soap without changing the volume of the soap fraction while the volume of the air decreases.  Alternatively, perhaps the volume of the liquid soap can decrease (density would increase) due to the molecules “packing” together with time.




Yes I agree it does seem to be some sort of reaction so I am hoping someone can confirm the chemical process going on


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## Karen jw (Jul 23, 2019)

HaniS said:


> Carbon dioxide. The reaction still needs Oxygen and it's trying to absorb it from the outside.


This would make sense. I thought the process with liquid soap is finished by this point though. Is this a known phenomena?


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## Karen jw (Jul 23, 2019)

Pictures.
This is after equalising the pressure once. It was worse the first time around.


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## HaniS (Jul 23, 2019)

I can think of the reason why the bottle is collapsing in this sense: The breakdown of the triglyceride inside of the bottle emits carbon dioxide. The Carbon dioxide that becomes dissolved in the liquid (water) produces carbonic acid. Carbonic acid neutralizes the potassium (or sodium) hydroxide in the solution. This result in the conversion of gaseous carbon dioxide to an aqueous solution of sodium carbonate (soda ash). As the amount of carbon dioxide decreases, the pressure inside the bottle decreases while the atmospheric pressure on the outside remains the same, leading to a collapsing the bottle.

From another point of view, the reaction of KOH, water and the triglyceride (olive oil) might still be active and emitting heat. The heat causes moisture vapor to migrate and pass throughout the bottle’s cap. And as a result, the volume of the contents is reduced and the bottle wall sucks in to compensate for that loss. This is because Oxygen is not absorbed back to balance the pressure between the inside and the outside.

I can think of Mobjack Bay’s point of view also. The molecules “packing” together in order to prevent or compensate the loss or the need for oxygen, and creating an (inward stress) to compensate and acquire oxygen by creating an absorption force.

Did you bottle the liquid soap soon after you finished the reaction? And how much water did you use or add? Also how much KOH did you use?

note: if it's KOH that is being used then it potassium carbonate not soda ash (sodium carbonate)


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## Karen jw (Jul 23, 2019)

HaniS said:


> I can think of the reason why the bottle is collapsing in this sense: The breakdown of the triglyceride inside of the bottle emits carbon dioxide. The Carbon dioxide that becomes dissolved in the liquid (water) produces carbonic acid. Carbonic acid neutralizes the potassium (or sodium) hydroxide in the solution. This result in the conversion of gaseous carbon dioxide to an aqueous solution of sodium carbonate (soda ash). As the amount of carbon dioxide decreases, the pressure inside the bottle decreases while the atmospheric pressure on the outside remains the same, leading to a collapsing the bottle.
> 
> From another point of view, the reaction of KOH, water and the triglyceride (olive oil) might still be active and emitting heat. The heat causes moisture vapor to migrate and pass throughout the bottle’s cap. And as a result, the volume of the contents is reduced and the bottle wall sucks in to compensate for that loss. This is because Oxygen is not absorbed back to balance the pressure between the inside and the outside.
> 
> ...





HaniS said:


> I can think of the reason why the bottle is collapsing in this sense: The breakdown of the triglyceride inside of the bottle emits carbon dioxide. The Carbon dioxide that becomes dissolved in the liquid (water) produces carbonic acid. Carbonic acid neutralizes the potassium (or sodium) hydroxide in the solution. This result in the conversion of gaseous carbon dioxide to an aqueous solution of sodium carbonate (soda ash). As the amount of carbon dioxide decreases, the pressure inside the bottle decreases while the atmospheric pressure on the outside remains the same, leading to a collapsing the bottle.
> 
> From another point of view, the reaction of KOH, water and the triglyceride (olive oil) might still be active and emitting heat. The heat causes moisture vapor to migrate and pass throughout the bottle’s cap. And as a result, the volume of the contents is reduced and the bottle wall sucks in to compensate for that loss. This is because Oxygen is not absorbed back to balance the pressure between the inside and the outside.
> 
> ...



This is the recipe I used.
I didn't measure the amount of water I added altogether as it was over the course of a day or two. I didn't want to make it too thin by throwing in too much water at once.
It was bottled about 2 days after processing.


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## HaniS (Jul 23, 2019)

KOH seems to be almost right, slightly increased though. To the best of my knowledge, the water used is being incorporated over two stages.  The first time is when KOH is dissolved in it to produce the water/lye and react the oil with it. By looking at the recipe I can see that first amount of water. After few days of settling the liquid soap, without covering it yet, more water is being added - usually at least another 100 grams to this recipe. I used to add more, about 200 grams relative to this recipe. But as you said, this is up to you if you want to make it more concentrated. But again as far as I know, the second amount of water is added without further heating, and the mixture is left to cure for at least couple of weeks or more to neutralize. I'll try and look it up again, and find a resource to confirm this. The last time I made olive oil liquid soap was probably 15 years ago!

Also by looking at the picture, the top fatty layer indicates that the soap still hasn't fully reacted, there's free fat on top. So it seems like it needs more heating. I checked one site, and found that adding more water is there. But the (maker) added the water soon after she finished cooking the soap. From a chemical/ reaction point of view, the liquid soap should be allowed more time to cure gradually. I'd use a prolonged (or repeated) hot water bath to speed up neutralizing..


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## Karen jw (Jul 23, 2019)

HaniS said:


> KOH seems to be almost right, slightly increased though. To the best of my knowledge, the water used is being incorporated over two stages.  The first time is when KOH is dissolved in it to produce the water/lye and react the oil with it. By looking at the recipe I can see that first amount of water. After few days of settling the liquid soap, without covering it yet, more water is being added - usually at least another 100 grams to this recipe. I used to add more, about 200 grams relative to this recipe. But as you said, this is up to you if you want to make it more concentrated. But again as far as I know, the second amount of water is added without further heating, and the mixture is left to cure for at least couple of weeks or more to neutralize. I'll try and look it up again, and find a resource to confirm this. The last time I made olive oil liquid soap was probably 15 years ago!
> 
> Also by looking at the picture, the top fatty layer indicates that the soap still hasn't fully reacted, there's free fat on top. So it seems like it needs more heating. I checked one site, and found that adding more water is there. But the (maker) added the water soon after she finished cooking the soap. From a chemical/ reaction point of view, the liquid soap should be allowed more time to cure gradually. I'd use a prolonged (or repeated) hot water bath to speed up neutralizing..


Thank you that's interesting and most helpful. I'll try that and look forward to confirmation of the process and curing timing.
I was quite surprised to see free fat appear as I used a 0% superfat to avoid that and had cooked it for longer than instructed and there was no zap on testing.


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## HaniS (Jul 23, 2019)

It looks like a great start anyways! Liquid Olive Oil Soap is so special as far as I remember when I used it, it has a unique effect especially to the hair.. What I think happened, is that you might have exceeded the amount of water that is required to achieve the reaction during the initial stage, which resulted in low concentration of KOH. Never the less this can be corrected by heating the soap again. KOH reacts slowly with oil. This is why a relatively small amount of water should be used to achieve the first saponification. Usually the soap turns into a paste not liquid yet after finishing the first stage. It's left to cure to advance the reaction and allow further neutralization. After few days the additional amount of water is added and the soap is not stirred yet. It's left to emulsify with the water. Then it's stirred every few days slowly, as it starts to become more clear and stable.

I'm sure that you will find a way to work it out and have a great all-natural liquid olive oil soap..


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## Karen jw (Jul 23, 2019)

HaniS said:


> It looks like a great start anyways! Liquid Olive Oil Soap is so special as far as I remember when I used it, it has a unique effect especially to the hair.. What I think happened, is that you might have exceeded the amount of water that is required to achieve the reaction during the initial stage, which resulted in low concentration of KOH. Never the less this can be corrected by heating the soap again. KOH reacts slowly with oil. This is why a relatively small amount of water should be used to achieve the first saponification. Usually the soap turns into a paste not liquid yet after finishing the first stage. It's left to cure to advance the reaction and allow further neutralization. After few days the additional amount of water is added and the soap is not stirred yet. It's left to emulsify with the water. Then it's stirred every few days slowly, as it starts to become more clear and stable.
> 
> I'm sure that you will find a way to work it out and have a great all-natural liquid olive oil soap..



That makes sense. I'll try some again soon and follow your tips and hopefully have a less problematic experience. I'll let you know how I get on fixing this soap and if I have any other problems I'll no doubt be back for some more expert advice. Thank you most kindly


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## Saranac (Jul 23, 2019)

www.oberk.com/packaging-crash-course/plastic-bottle-paneling-5-causes-and-the-cures

I'm leaning towards Causes #2 and #3 in the above article.  I've had full bottles of LS do this, so I ruled out #2 when it occured to me.  Temperature fluctuations, pressure changes, and the gas permiability of your bottle all seem at play.


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## DeeAnna (Jul 23, 2019)

Saranac said:


> ...Temperature fluctuations, pressure changes, and the gas permiability of your bottle all seem at play.



Yep, my thinking too. A thin walled bottle will buckle simply from ambient temperature and pressure changes, especially if there is a lot of headspace (air) in the bottle to expand and contract due to environmental changes. A tall, narrow cylinder shape doesn't have much rigidity simply due to its geometry, so that will also contribute even more to a lack of stability.


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## Karen jw (Jul 23, 2019)

Saranac said:


> www.oberk.com/packaging-crash-course/plastic-bottle-paneling-5-causes-and-the-cures
> 
> I'm leaning towards Causes #2 and #3 in the above article.  I've had full bottles of LS do this, so I ruled out #2 when it occured to me.  Temperature fluctuations, pressure changes, and the gas permiability of your bottle all seem at play.



Yes I'm thinking 2 or 3 and if it happened to you with a full bottle then 2 is likely not the cause here either. Also the ambient temperature has been increasing drastically here over the last few days so if temperature alone were responsible I'd be seeing pressure build as well as drop but it's only been dropping.
It's a very flimsy bottle being from cheap generic cola so I think reason 3 could be the most likely.
Very interesting indeed


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## Mobjack Bay (Jul 23, 2019)

Karen jw said:


> Yes I'm thinking 2 or 3 and if it happened to you with a full bottle then 2 is likely not the cause here either. Also the ambient temperature has been increasing drastically here over the last few days so if temperature alone were responsible I'd be seeing pressure build as well as drop but it's only been dropping.
> It's a very flimsy bottle being from cheap generic cola so I think reason 3 could be the most likely.
> Very interesting indeed


If there was no gas buildup in the headspace for the other poster, then #3 is not likely.  The gas would be much more likely to collect in the bottle and cause the sides to bulge compared with escaping out through the container walls. I ruled out ambient changes in pressure and temperature because it happened twice. That suggested to me that the soap itself was actively changing.


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## DeeAnna (Jul 23, 2019)

And remember that the plastic in these flimsy bottles can be slightly deformed or weakened from being washed, moved around, heated/cooled, etc. If there is a slightly weaker part of the bottle, any distortion will show there first. 

The super-thin bottles of drinking water that I have in my pantry show similar deformation just from sitting quietly at ambient temperature on a shelf. They look fine when new, then gradually deform as time goes on.


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## Zany_in_CO (Jul 23, 2019)

Good discussion. Although I wasn't able to contribute to why the bottle weirded out, here are my comments about your recipe.

As I long-time member of a liquid soap making group, 100% olive oil castile is one of the most challenging to make. It takes a long time to trace (45 minutes for me) and a long time to cook (3-9 hours on average; 10 hours for me the first time) until it tests neutral for lye excess.

TIPS:
Be sure your SB has a stainless steel shaft... the high heat of making LS can melt plastic.

Because OO has "unsaponifiables" you were correct to use 0% SF and 90% KOH. The thing to keep in mind though, is, once you know your KOH amount, you need that number X 3 for your water amount to make the lye solution -- due to evaporation during the long cook. There is a place on SoapCalc.net where you can enter 3:1 *Water to Lye Ratio*





Dilution: While 100% coconut oil and more balanced formulas will dilute nicely at 40% soap to 60% dilution water, the recommended dilution for 100% OO is 15% Soap to 85% water. This results in thin soap but with excellent lather and cleansing properties. You will then need to thicken with brine solution (or thickener of choice).

Viscosity is, of course, a matter of preference. But the high viscosity of your finished soap means that a lot of it goes down the drain and it takes longer to rinse off. My recommendation is to take a portion of the soap, say 100 grams, and try the 15 grams to 85 grams ratio to see how you like it. I think you will be surprised at the feel of the lather and how well it cleans. I know I was! LOL

There's good info plus Tips & Tricks about making liquid soap in the link below. Faith also has a tutorial on making 100% OO using the glycerin method (which is what I do), but it is an advanced technique, dangerous due to the high heat of the lye solution, so I don't recommend trying it until you have a few more batches under your belt.

*http://alaiynab.blogspot.com/search/label/tutorial*

HAPPY SOAPING!


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## Karen jw (Jul 24, 2019)

Zany_in_CO said:


> Good discussion. Although I wasn't able to contribute to why the bottle weirded out, here are my comments about your recipe.
> 
> As I long-time member of a liquid soap making group, 100% olive oil castile is one of the most challenging to make. It takes a long time to trace (45 minutes for me) and a long time to cook (3-9 hours on average; 10 hours for me the first time) until it tests neutral for lye excess.
> 
> ...




That's really helpful info.
Yes it did take around that long to get to trace but I was expecting that with the pure oo. I did the zap test after I thought it was fully cooked and there was no zap at all and it had cooked to a thick clear jelly so I thought it was finished. 
Loads of really helpful info here. 
So glad I posted this question.
Thank you all


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## DeeAnna (Jul 24, 2019)

Once the soap paste is zap free, it's done. You can choose to cook it longer, certainly, but you don't have to. I make liquid soap from 100% sunflower, which is even higher in oleic acid than olive oil, and it's usually done in under an hour ... two hours tops if I'm out of practice.

Or get the paste to trace, cover it tightly, set it in a safe place at room temperature, and let it finish saponifying that way. It will take longer than if it is cooked, that's true, but it WILL fully saponify and make fine soap with zero fiddling and fussing.

The hours 'n hours of cook time have given liquid soap a bad reputation that is undeserved.


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## Nanette (Jul 24, 2019)

I'm Never making liquid soap.


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## Karen jw (Jul 24, 2019)

Haha Nanette. If you stick with a mixture of oils and not just pure olive oil, I'm pretty sure you won't have a problem. I just like to challenge myself haha.
And even though it has thrown up a couple of issues, I used some of the soap to make a dog flea shampoo using neem oil and some other essential oils. It left my two shihtzus so soft feeling that I decided to use some to wash my own hair. I'm very happy with the results. This was before I realised strange things were happening to the bottle


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## Zany_in_CO (Jul 24, 2019)

DeeAnna said:


> Or get the paste to trace, cover it tightly, set it in a safe place at room temperature, and let it finish saponifying that way. It will take longer than if it is cooked, that's true, but it WILL fully saponify and make fine soap with zero fiddling and fussing.


*@Nanette *This is SO true, and easy peasy. One of the most difficult judgment calls for those who are new to making LS is whether or not they have cooked the paste long enough. Finishing saponification this way eliminates that problem. I know many soapers who use this method. I've done it myself. I just let it set for 2 weeks and I have a beautiful honey-colored neutral blob of soap ready to dilute.


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## Karen jw (Jul 25, 2019)

Update.
The bottle is still doing weird things. Not worried any more it's stupidly flimsy. I'll use a better one next time.
As for what appeared to be free fat floating in the top.....
I added some more water.
The free fat appears to have actually been a very fine layer of bubbles trapped due to the high viscosity.
This makes total sense as there was no zap so the soap was done and the superfat was 0% so there shouldn't have been any free fat. I'm now very happy indeed with my successful liquid Castile soap.

Thank you everyone for your help and insight as well as some great advice that I'll be taking into my next batch and beyond.
Oh and next time I will use regular olive oil rather than extra virgin which should give me a better chance of producing a nice clear soap!


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