Curing & other implications of hermetically sealing lye soap immediately after cutting?

[Garden Gives Me Joy]

I notice that my brine soaps are at their lowest ever weight immediately after I have processed them. The weight only increases afterwards. I believe this is because I am in an extremely humid (tropical rainforest) climate that makes salty soap sweat endlessly, especially when it rains. So I guess the salt generally attracts more water to the soap rather than allow water to evaporate as the soap cures. I have doubts about running a fan incessantly for 6 weeks. It does not help that we often have power outages.

Some noteworthy points about how I processed brine soap.

• water as a percentage of oils: 22.5%
• Although I use cold process, I emulsify when the lye is at its hottest (at roughly 78 C) / 172 F) after it has dissolved fully (usually within a minute of adding NaOH). To match the temperatures of the oil and lye, I heat the oil before adding the NaOH to the water so that the oil is already at the 'high' lye temperature, roughly 78C. I have even begun to emulsifying & blending within a hot water bath. I wanted to evaporate away as much of the water as possible, to hopefully accelerate curing and release as much water as possible.

In light of water absorption issues, what are the implications of wrapping the soaps in airtight wrap immediately after cutting, roughly 2 to 4 hours after pouring, depending on the recipe? (The soaps would be too brittle if I cut them any later). Would the absence of oxygen be problematic chemically or otherwise somehow?

 

[amd]

Hang with me for a second here... when making soap dough one of the things that keeps it moldable and pliable is wrapping it well after saponification, slowing the cure process and preventing the soap from drying out. I think the same thing will happen to your brine soap if you wrapped it immediately after cutting - you would be slowing the cure process and keeping the soap, maybe not in a pliable condition, but a much softer bar than if you allowed it to cure with air flow. The end result would be a soap bar that uses up much more quickly. If this is acceptable for personal use, then this may be an option to consider, but if you are selling, I don't think you would be putting out the best product.

 

[Todd Ziegler]

You are right about salt. It's what you call a humectant, they are what makes something a long lasting moisturizer.

About sealing your soap within 2-4 hours. I wouldn't recommend doing that, because regardless of how much the soap attracts water, the soap needs air to cure and that can't happen in an airless environment.

Second, trapping moisture in could lead to other problems. Even though the salt in your soap will kill a lot of bad critters, you will run the chance that a spot in the soap not having enough salt to kill the mold or fungus.

It’s a hard spot to be in but I would not wrap them air tight until you are ready to ship/sell them.

Hopefully someone else will chime in and either correct me or add to what I have said.

 

[AliOop]

You might try the reverse - MORE water in your salt bars may allow them to equalize more easily in your humid environment, and thus, they will sweat less. Try a small batch to see what happens!I

Otherwise, if you still want to try for less water in your uncured bars, here are a few thoughts:

1. Use the lye concentration setting instead of water as % of oils. That will give you a more consistent water percentage as you scale the batch up or down. I regularly use 40% lye concentration and have no trouble with tracing faster than it already does for the particular recipe in use. Because they have less water to begin with, my soaps unmold sooner and shrink less during cure. I still think that might have the reverse effect of what you are seeking, and that they will attract more water bc they are drier, but it's worth a try.

OR

2. With your hot lye, hot oils and hot water bath, you are almost HP'ing your soap ... so give HP a try. It is less fiddly and more straightforward than a hot water bath, IMO. You could start with a 25% lye concentration and see how that works for you. For an HP salt bar, I don't recommend cooking to mashed potatoes, however. Vaseline stage is good enough so you can still get it into the mold without too many pockets or too much of a "rustic" effect. I wouldn't try fluid HP, however, since that requires way more liquid, which kind of defeats your goal of minimizing the water in your final product. Tip: I do my HP in a stainless pot on the stove, or in the stainless liner my IP. A heavy crockpot liner is too hard on my wrists and too messy when I'm trying to get the soap into the mold.

 

[ResolvableOwl]

@amd Hrm. Soap dough. I have successfully converted cured soap back to soap dough by soaking them in water. From this perspective, @Garden Gives Me Joy's initial idea of instant wrapping might be the best thing to do (without changing recipe/process). You'll have to use many hard oils anyway in your climate, and a soap dough that is a bit “too hard” might well be just a fairish bar of soap at room temperature/becomes pliable not until reaching temperatures that aren't common in the bathroom. Give it a try! Curing is something that happens irrespective of water content. Soap dough cures, TD-bearing CPOP soaps cure to form glycerin rivers, M&P base cures.

Besides this, I think a classic HP might well be worth a try as well. Just be cautious when you add the salt (I'd do it as late as possible), to not accidentally salt-out the soap batter.
Well, or deliberately salt-out the batter! That way you get rid of much of the glycerol, which is a major contributor to the hygroscopic nature of soap.

 

[earlene]

As a matter of fact, the last time I made salt bars, the humidity in my home was really quite high, so I shrink wrapped them quite a bit earlier than I normally do with other soaps. They were plenty hard when I eventually took them out to use them and I know they cured because the quality of the soap improved over time as cured soap does.

My 4 week young salt bar soaked up water when I took off the shrink wrap in Hawaii and just left it out open to the natural humidity. This was before I even used it, so yes, in a tropical rain forest area salt bars are going to soak up the ambient moisture, no matter what their age, although in my experience it takes longer for an older (over a year cure) salt bar to start beading up than it does for a younger salt bar in the presence of high humidity.

 

[Garden Gives Me Joy]

So very thankful for your feedback and suggestions.

If possible, I would prefer to consider other workaround options before changing my recipe.

AIR?
Does soap really need air in order to cure? Are there certain conditions to its necessity? @Todd Ziegler suggests that "soap needs air to cure". Conversely, @earlene got "plenty hard" bars that "cured [... well and whose] quality [...] improved over times ..." when she wrapped her soap "quite a bit earlier than [...] normal [...]". @earlene, would you mind please saying how much time after pouring you wrapped your salt bars?


LONGER CURING TIME FOR HARDER / DURABLE BARS?
I gather from @amd that sealing soap at any stage slows its curing process and in turn prevents the soap from hardening than would have been the case otherwise. Since my brine recipes produce very hard bars from within a few hours, would a longer cure period resolve any potential sub-optimal hardness if I wrap within hours after cutting?

@earlene , Do your salt bars seem to need significantly more curing time overall than usual to get to an ideal state of being cured after you have wrapped them 'prematurely'?


MOLD & OTHER NASTIES?
@Todd Ziegler 's good point re "trapping moisture in could lead to other problems" leads me to my other question. When soapers wrap to sell, what is an acceptable percentage of water that remains in the soap after curing (roughly 6 weeks after pouring)? Should I assume that any weight below my initial total weight of ingredients is due to water evaporation (ie that no other ingredient could have evaporated or otherwise dissipated ... and of course, taking into account the tidbits left in mixing bowls whose weight can be determined if we know the weights of our mixing bowls, etc)?

@ResolvableOwl suggests that "curing [...] happens irrespective of water content." My personal observation suggests the same. So! What if I attempted to evaporate out ALL of the water before pouring? Would that just resolve the potential for nasties? (Don't know what TD means). I am not concerned with glycerin rivers and the sort. I get @amd 's point re a dried out soap. However, I am hoping that the environment will resolve that issue very quickly once the soap is unwrapped, because the soap will start attracting moisture from the air.

BTW, I have decided to completely exclude mold-loving ingredients (like carbs) in my brine bars. They only have additives like clay and charcoal. (Turmeric might be mold inducing but I have never seen it in my acid tests). But I am unsure what causes fungus and should probably look that up I suppose.

 

[amd]

I gather from @amd that sealing soap at any stage slows its curing process and in turn prevents the soap from hardening

To correct this slightly - wrapping does not prevent the soap from hardening, it slows it down. Sorry if I gave that impression. Even well wrapped soap dough will eventually harden.

 

[ResolvableOwl]

Good write-up, I can understand you so well, sometimes this is needed to squeeze the important bits out of such a thread. Though, you still have no definite answer/help for your further steps.

A few annotations:
TD means titanium dioxide (white pigment), which isn't directly relevant for your case, I mentioned it because with TD & glycerin rivers, one can “watch” part of a curing process (reorganisation of soap molecule crystals) with bare eyes over a short amount of time.

evaporate out ALL of the water before pouring?

I don't quite understand? Mixing oils and NaOH (and other ingredients like salt) but without water would possibly be marvelous, but it isn't possible; you'd start with a rock-hard bar that, well, isn't pourable at all. Lye concentrations at >40% do all they can to prepare soap with as little water as possible, but there is just no way how this could achieve a soap that has no (excess) water just at the moment of making. You'd need lye concentrations of some 70% or higher, which is impossible for obvious reasons. Adding table salt makes this even worse.

Should I assume that any weight below my initial total weight of ingredients is due to water evaporation (ie that no other ingredient could have evaporated or otherwise dissipated

Except for FOs to a very limited degree, there is nothing in soap that is volatile at room temperature. So any weight loss really is a water loss. There is one process that can increase the mass of a soap, if only by minute amounts: formation of soda ash (this isn't limited to the surface, but also happens inside the soap bar, though invisible, and leads to a moderation of lye heavy soap on the long run, i. e. old-fashioned castile recipes).
But this leads me to another (hopefully stupid) question: You've said that the soaps become heavier with time. You have weighed the bars just after unmoulding/cutting/planing/bevelling, and then some time later? Or have you just compared the weight of the bars to the numbers in your recipe?

A final point regarding @Todd Ziegler's objection against early wrapping and “nasties”: As far as I understand it, this is based on the assumption that soap loses water with time, i. e. any solutes therein increase in concentration, and become deadlier for bad bugs. But exactly this appears to not be the case for you. Pulled water from the air might foster microbial decay, just like pulled water from moist basement air fosters mould stains on walls and wood/paper rotting (just as an example that free air flow does not always improve longevity). So, as useful as his approach is for well-behaving cosmetic products, in your case it appears more like a “no predictive value unless further testing has been carried out”.

 

[Garden Gives Me Joy]

You've said that the soaps become heavier with time. You have weighed the bars just after unmoulding/cutting/planing/bevelling, and then some time later? Or have you just compared the weight of the bars to the numbers in your recipe?

I weighed the soaps when I poured them into single-bar molds. I then weighed them at different times where the only thing that changed was the time. The bars just remained in the molds. In addition to seeing that the soaps were sweating, their weights continued to rise with time once they cooled down. Examples:

Soap 1:

• at pour: 56 g
• day 6: 56.9 g
• day 17: 57.7 g

Soap 2:

• at pour: 53 g
• hour 1: 52.9 g
• hour 4.5: 52.7 g
• day 6: 53.7 g
• day 17: 54.6 g

I have not yet tried to contrast weights of the recipe against the batter at pour. To calculate how they contrast, I figure I would account for all of the batter (including what is left over in the mixing bowls) and then assume that any shortage is due to water loss.

When I mentioned evaporating away all of the water, I really do notknow how much evaporation is actually possible. That is why I am eager to know what extremes are acceptable and possible. I was trying to go to extremes with high mixing temperatures and the hot water bath and would push the envelope further if it were possible to do so with good results.

 

[ResolvableOwl]

Okay, that is unambiguously a mass gain. Not much, but it's significant that they will never lose weight under your climate conditions (btw, wind/ventilation won't help much, maybe even worsen it).

By comparing soap weight with recipe size, you're mostly measuring your process losses (how much is dripped, stuck at the stick blender, in bowls, on spatulas etc.), not so interesting from the mass-change-by-evaporation point of view.

From the NaOH solubility, 50% lye concentration is about the maximum that can be achieved halfways reliably with CP. I haven't tried it, but it might be of some help for you to start off at a lower initial water content.
The maximum lye concentration in HP is probably lower, since you'd need some extra water to keep the batter fluid enough to not end up with soap-on-a-stick. Though maximum NaOH solubility increases with temperature, CP (with some heat assistance) is better in this respect.


ETA: To determine equilibrium moisture content of well-behaved soaps (in well-behaved climate), there are some drying curve experiments out there; the one from DeeAnna as well as mine on a super slow castile come to my mind.

 

[earlene]

@earlene, would you mind please saying how much time after pouring you wrapped your salt bars?

That batch of soap was over 3 years ago, I honestly don't recall exactly. I know if was less than 4 weeks because I shrink wrapped them and took a couple of them to Hawaii with me when they were about 4 weeks old so I could experiment with humidity higher than my own.

LONGER CURING TIME FOR HARDER / DURABLE BARS?
I gather from @amd that sealing soap at any stage slows its curing process and in turn prevents the soap from hardening than would have been the case otherwise. Since my brine recipes produce very hard bars from within a few hours, would a longer cure period resolve any potential sub-optimal hardness if I wrap within hours after cutting?

@earlene , Do your salt bars seem to need significantly more curing time overall than usual to get to an ideal state of being cured after you have wrapped them 'prematurely'?

I really cannot say for sure. I am not a huge fan of salt bars, mostly because it takes a really long cure before my skin can tolerate them (close to 3 years, regardless or whether the soap was wrapper early or not); perhaps it is the high CO content or perhaps it is all the salt that feels so abrasive on my skin.

MOLD & OTHER NASTIES?
@Todd Ziegler 's good point re "trapping moisture in could lead to other problems" leads me to my other question. When soapers wrap to sell, what is an acceptable percentage of water that remains in the soap after curing (roughly 6 weeks after pouring)? Should I assume that any weight below my initial total weight of ingredients is due to water evaporation (ie that no other ingredient could have evaporated or otherwise dissipated ... and of course, taking into account the tidbits left in mixing bowls whose weight can be determined if we know the weights of our mixing bowls, etc)?[/quote]
I refer you to Marie Gale's excellent information about determining final (net) weight of soap (for the purpose of creating a label that will be accurate even if said label is made prior to complete cure.):
https://www.mariegale.com/calculating-net-weight-soap-part-1/https://www.mariegale.com/calculating-net-weight-soap-part-2/
Just for the record, all the moisture is NOT trapped inside when I shrink wrap my soaps, nor when many others here shrink wrap their soaps. Over time the soap still looses weight and the wrap can become loose, requiring a quick application of the heat gun to tighten the shrink wrap up again if the soap sits around for a long time (many sellers have mentioned this.) Is that true of all thicknesses of shrink wrap? Probably not, as what we buy for soap wrapping is not the heavy duty shrink wrap. Many soapers use 'smell-through' shrink wrap, like I do, and it allows the fragrance to be sniffed when the product is held close to the nose. If the wrap is permeable to odor, it is bound to be permeable to oxygen to some degree, as evidenced by the soaps inside getting smaller over time (water loss).

@ResolvableOwl suggests that "curing [...] happens irrespective of water content." My personal observation suggests the same. So! What if I attempted to evaporate out ALL of the water before pouring? Would that just resolve the potential for nasties?[/quote]
Well, then, you wouldn't be able to pour it, as it would be a solid.