Moldy soaps, Storage, Packaging, Shelf Life

[Garden Gives Me Joy]

This image is from a batch of soap I made on 27 May, 2020 using the HP.

Why did these moldy spots appear? ... and isn't it odd that the molding happened to only these 3 out of the 10 bars that had been tumbled together in a sealed plastic bag?

The water content was at the rate of 38% of oils. The bars are actually hard and durable. They do not have any purees. I also added a little peppermint oil (at apx 1.5% of oils), along with superfat after the HP cook. In fact, the peppermint is still mildly perceptible in scent and sensation. I thought the mint would have helped to protect, certainly within only 3 months, but clearly not.

This batch has only been for my personal use. A sample soap used to test through washing my hands was tossed back in with the rest after it had dried. Could this have been the culprit, especially since I am in a high humidity environment? Does anyone else ever store soaps badly to see if they can withstand the bad treatment as a type of 'acid test' for undesirable shipping, handling, storage conditions and shelf life? Happy for advise and your stories. Most soaps have remained fine, especially the very hard ones beyond 9 months and 1 year without mold. I figure that the better way to store the soaps would be in a box that is closed but still breathable. Do high humidity storage conditions cause mold to appear? Is this only an error of tossing back in the sample or could it be something else?

These crazy experiments leave me uncertain re the extent to which packaging should have breathable vents.

 

[Obsidian]

I'm just guessing here since I've never seen soap mold like that. I'm going to blame the added SF along with the used soap being sealed up in a plastic bag.
Even if you let the bar you used, dry off, it still had excess water in it.

I've never stored soap in plastic, mine goes in paper bags on a shelf in the closet.

I won't even wrap in plastic for shipping. I really feel that soap needs air flow, even after cure.

 

[AlexanderMakesSoap]

+1 on not keeping them sealed up in plastic bag - seems like airflow would be better, and combine that with the fact that you tossed one in that put one back after exposing it to your hand-germs...trouble!

I dry mine on racks and then leave them in cardboard boxes after that.

 

[msunnerstood]

I have to agree. I HP but my bars sit out in the open to cure for 4 weeks before I wrap them. I had a soap scrap bucket I mistakenly covered in between adding scraps. A piece that was still moist wound up in there and within a few days the bucket stunk to high heaven and I had to throw the scraps out.

 

[shunt2011]

I’ve never seen anything like that before either. I’m going to have to agree with the storing them in plastic bags. Yikes.

 

[earlene]

Supposedly mold cannot grow in the high pH conditions of bar soap, but that certainly does look like mold! And it's not the first report of mold growing on bar soap. Still without some feedback from a scientist, it is rather a mystery.

I wonder if you could send a bar to Dr. Kevin Dunn and ask him if he would be willing to provide some scientific information on the subject that then you could share with the rest of us. He is a university chemistry professor who specializes in soap and frequently does presentations at soap conferences around the country. He has also written a book, titled Scientific Soapmaking, so he is really into the chemistry of soap.

As I think about it though, I wonder since mold is supported by the presence of water and other organic material, perhaps there was enough of the superfat (added after saponification had completed, right?) on the surface of the soap and some mold spores got into either the water or the bag in which you stored the soap, and the conditions worked in the mold's favor in spite of the pH on the surrounding soap.

 

[DeeAnna]

I've looked several times at the OP's photo, and I'm finding it hard to believe there's just fat, water, and lye in this particular soap. There is a lot of variation in texture and color that's unusual for a simple, basic bar of soap. The moldy areas seem to be on larger pale-colored spots, which makes me think those spots are something other than plain ol' soap.

 

[TheGecko]

What did you use as a super fat? I

 

[Catscankim]

Most soaps have remained fine, especially the very hard ones beyond 9 months and 1 year without mold. I figure that the better way to store the soaps would be in a box that is closed but still breathable

Im in no position to give advice, but you said “most soaps”....do you have other soaps with this mold?

 

[Nostalgicgranny]

You mentioned no purees. Did you add any botanicals? Oatmeal, herbs, etc. What was your recipe?

 

[Garden Gives Me Joy]

Supposedly mold cannot grow in the high pH conditions of bar soap, but that certainly does look like mold! And it's not the first report of mold growing on bar soap. Still without some feedback from a scientist, it is rather a mystery.
I wonder if you could send a bar to Dr. Kevin Dunn and ask him if he would be willing to provide some scientific information on the subject that then you could share with the rest of us.

I've looked several times at the [..] photo, and I'm finding it hard to believe there's just fat, water, and lye in this particular soap.

@earlene Thanks for recommending Prof Keith Dunn. He and I finally had a chance to have a phone call earlier today. I had already sent him the image posted here. In addition to mentioning the bad storage issue, we also discussed the other non-oil ingredients. I trust that I have done justice to his generous comments below.

He suggested that the factors that contributed to the soap's mold may be one or a combination of the following.

1. Carbohydrates. Specifically, I used 3 tsp ppo oats and 1 tsp ppo sugar. Mold consumes carbohydrates (not oils). Many people use these ingredients without a problem. It is therefore worth also considering other possible factors. @DeeAnna , @Nostalgicgranny I did not have any fruit or vegetable purees. I assume purees will fit into this same category?
2. A low pH. Mold can not easily survive on soap that has a pH of at least 9 or 10. I did not know the soap's pH.
3. Moisture / Humidity. The soap was stored in a plastic bag that had trapped moisture.

Things to do

• Do a pH test using a 1% solution (NOT by resting a strip against a wet bar of soap). I used the only pH strips at my immediate disposal which have a range of 5 to 9. I scraped off soap from the surface of the soap about 1cm around a moldy area. The results of my 1% solution suggest that the pH is at least 9. (See video)*. We did not discuss my intentions to start using citric acid in all of my soaps. Re the citric acid, I will ensure that I always raise the NaOH by 6g for every 10g citric acid.
• Consider which offending factor(s) to adjust. This will entail determining the (desirable) properties you can sacrifice without losing the overall use experience. In this case, that is a matter of reducing my high superfat / lye discount rate (near 10%) and the carbohydrates. I figure that I really ought not resist when increasing the NaOH. I think I will need to reduce or eliminate the oats. [Sniffle!] I'm thinking I'll entirely replace the oats with kaolin clay. I used oats mainly because I wanted to dry out the soap a little more before turning off the heat and adding superfat. What is the usual / safe amount of oats? (I used HP). Otherwise, I might get a drier batter with a slightly longer cook at a low temperature.??? My immediate feeling is to safeguard the bubbly properties by maintaining the sugar, ie because I added 0.5 tsp salt in the lye water for hardness. The hardness score was 36. The soap's current hardness is good!

OTHER: When I asked whether adding vitamin E or R.O.E can help, he explained that those ingredients do not safeguard against mold (but rancidity and D.O.S, which were not problems in this soap).

@Catscankim I have seen strange dark brown spots on another similarly tossed aside batch after roughly 1.5 years.



* Just realize that videos can not be uploaded.

 

[earlene]

I am glad you contacted him. And thank you for letting us know how that went.

So it sounds like the oats &/or sugar + wet storage in a plastic baggie may have been the perfect environment. I will have to be more careful with how I store my travel soaps. I do tend to put them into a soap travel container that does not allow them to dry out as quickly as they do at home. They aren't really air-tight, but the amount of air-exchange inside my ditty bag is surely minimal.

As I review your first post, I realize you describe storing all the soaps in that batch in a big plastic baggy, incluing the one you had used to wash your hands. I would advise against ever storing used soaps in the same container as your curing/cured soaps. And never store the soaps together in a large plastic baggy in the first place. Lye soap (as opposed to MP soap) does better with air circulation. Even if you think they have sufficiently cured, there is still going to be some more water loss over time and in a plastic baggie, that water has nowhere to evaporate to, so it wall drip back down onto whatever is inside the baggie.

To answer your question about a safe amount of oats and sugar. I've never had mold from sugar, and I've not read of sugar being a problem with anyone here in regards to mold. I've only used colloidal oatmeal (finely ground oatmeal) and from what I read, one should follow the particular vendor's guidelines for the product, but if you grind your own, you don't have that reference. In this blogpost, The Sage recommends 1-6 tsp. per PPO if you grind your own. But when you say you

used 3 tsp ppo oats and 1 tsp ppo sugar

were the oats whole oats or ground oats? If they were whole oats (like rolled oats), then I'd said there is your problem. If they were ground oats, then I'd say it was just the complete package that contributed, with the potential wet storage playing a part.

Bar soap made with lye is going to have a pH of 9 or greater, so don't expect it to be less than 9 if you are making soap with lye.

Others who frequently use oats are bound to come along and provide additional answers.