Curing, packaging & formulating soap in highly humid environments

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Garden Gives Me Joy

Well-Known Member
Jan 25, 2020
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United States
My current location has a tropical rainforest climate and therefore experiences extremely high humidity. Issues include profusely sweating soap, soap weight gain during the cure period (a phenomenon I suspect is due to moisture), high probability of 'sweat' and mold on soap and packaging (like paper or string) that can wick water to skin-loving carbohydrate ingredients.

Examples: 'Zany's no-slime' Castile or Bastile soaps with minimal amount of salt at apx 3.5% ppo sweats and water slides out when the bottom of the container is drained. Just imagine what happened with some others of my higher percentage salt crystalline or brine soaps. You may also recall my other post (images included there) re how moisture in carbs likely contributed to mold.

To clarify, air conditioning is unfortunately not an option, not only for my current address (which is temporary, thanks to Covid-19) but also for others in my proposed distribution channel. Please give feedback and or add to my list of solution ideas and questions, especially those related to curing and packaging.

-- Formulating --
  • Use less or no:
    • Carbohydrates *
    • salt *
  • Use as little water as possible. *
  • Use batter drying ingredients that are also hostile to mold
    • Turmeric
    • ZnO? (It's used to prevent mold in paint. I don't know if that extends to soap somehow. Gave matte0p finish to Zany's no-slime Bastile but crumbly for another experiment with softer oils. Happy for comments).

-- Curing --
Dehumidifier. Does anyone have experience with this?
For the entire period, keep soaps next to a dehumidifier. This can be a calcium chloride (CaCl2) DIY dehumidifier. Is it effective and therefore worth the trouble trying to source the materials despite Covid. YouTube videos show variations, the most common & safe of which involves cutting a large pet bottle and inverting the top over the bottom section like a funnel. The cap is drilled with small holes that are too small for the CaCl2 to escape. Since CaCl2 is a desiccant, it attracts moisture and the funnel structure allows the condensation to become channeled down into the bottom section, the waste catchment.

Is a short period of solar dehydration just before packaging in plastic wrap a feasible idea? After all, won't it be like doing CPOP? (Video on the design of a solar dehydrator: ).

-- Packaging --
Is there a safe moisture percentage I should achieve to know all will be well if I could wrap in an airtight or very tight way with clingwrap? If so, to what extent should I quickly dehydrate just before wrapping still warm bars?

* ... more RE water in formulation process.
Outside the minimum 1:1 ratio required to dissolve NaOH, is there a minimum requirement for water for soap making? I read somewhere that there is more to curing (like chemical changes) than water evaporation. Would be happy for clarification. Does soap have at least some water, even when it can be considered fully cured and suitable for packaging? I read somewhere of label weights varying even after packaging 30, 60 and more days.

If a benchmark moisture percentage exists, how do I calculate weights? Specifically, apart from water that evaporates, are the original weights of all raw materials reliable for calculating weight at different times during the cure period? For instance, if raw materials were 450g fats, 60g NaOH and 190g water (ie 700g total) but, after cooking or curing, the total weight is 640g, should I assume that the weight loss occurred only with water and that the moisture level is therefore 20%? (ie 130g remaining water as a percentage of 640g )

Assuming this calculation is correct, I just tried a new HP batch that ended with just under 20% moisture post cook on 7 Feb (3 days ago). I barely got it in the mold and had to cut just after about 30 minutes. I suspect it would have been better if I had cut sooner. 2 of the 5 variants (with turmeric) crumbled badly, the one I thought "oh what the heck, I will add carbs, lots of it, namely dry rice flour" was the easiest to handle as it needed to be kneaded and felt like a firm but very compliant / malleable bread dough. I needed to press it against itself with my fingers into the mold. Some edges broke away when I was cutting it but the bars are rock hard and dusty dry. BTW, the formulation had no salt, sugar or other carbs. I suspect I caught the 'mashed potatoes' phase very late. I had forgotten how quick and drama-free (no separation, etc) HP is without additives. Water was 36%. Since there was 0.5% stearic acid, I tried keeping heat over 71C, up to 80C to be precise. Perhaps it's ok to lower the heat after the emulsion and trace have clearly passed, especially since I already know there's no trouble with separation that could pose problems for stearic acid. ???

* ... more RE carbs, salt & I other lovely ingredients in formulation process.
If it is feasible to protect the soap, even from humidity that exists in the environment of distribution channel players and consumers, can I go back to using carbs and salt ... and instruct consumers to open only before use? If I introduce additives like oat flour when there is as little water as possible, should that prevent them from being 'activated'? ... but would they have enough time to become activated in the shower?

It's only been a few days since my last experiment so I don't know yet if mold will grow. Happy for your thoughts!
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Sep 15, 2018
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First off, I'll apologize because my reply is to your thread title lol. I tried to read the rest twice but maybe I need more coffee first........

Anyhow, I am in the Philippines. Humidity at its best lol with extremely humid days followed by lots of rain. Plus heat. Ugh.

Packaging: I do not wrap my soaps til right before they're to be sent out. FYI, I use paper and twine/jute. I learned my lesson when the ink on the labels got transferred onto the soap, and this happened when they sat on the counter (not where I cure them) for about 4 days.

Water n Curing:
My salt bars and soleseifes are on the shelf closest to the dehumidifier - a recent purchase, and has helped loads - directly facing the rack. They will sweat even after curing for a year btw, because the glycerin in handmade soap will always draw water in.

Imagine what happened when we were flooded lol

That being said, my triple rice soap (rice water, Rice Puree and rice flour) sweats the least, followed by my lard soaps. I HP too, and my water ranges from maybe 2.3 - 2.6 : 1 lye ratio, depending on the recipe. More than that then the bars warp horribly, less than that and it gets difficult to mold and swirl

Zany's no slime ranks somewhere near the high salt soaps..... And I used less than 2:1 water here when I made mine.

Before the dehumidifier I had a ceiling fan running constantly in the room where they were. Once the soap has cured and I needed space in my shelf I transferred them into boxes with raw rice grains in the corners, with the lid partly open, still in the same room where the fan is running

My slight advantage is every now n then the AC gets turned on, so the fan can get a bit of rest lol

I have not gotten mold on my soap. Ever. I use a lot of plant powders and pureed stuff. Your chances will increase if you use chunky food bits (I have to point out though, that my pureed banana soap never got mold too, I have a couple of bars that are more than a year old now) that have not been saponified with the rest. In my head that means don't add the food bits after cooking lol

Err... If I've not covered anything, please remind me lol I'll just go make that coffee...

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