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Food stuffs in soap and preservatives

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KimT2au

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Hi all

I have been watching videos and reading posts about people using things like pumpkin puree and sweet potato puree in their soap and how yummy it is. I understand that the purees have combined with the soap and the portion of the puree that is enclosed within the soap is starved of oxygen and therefore will not grow bacteria etc but what about the purees that are on the outside of the bar? Do these bars need to have a preservative added to them to stop the foodstuffs from becoming a breeding ground for bacteria?

Kim
 

shunt2011

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I’ve made soap with pumpkin and have never had an issue. As long as it’s blended well it’s fine. I have a bar that’s 3 years old and still a good soap. I add the purée to my oils and mix well then add my lye mixture.
 

Relle

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I too have a bar that would be about 4 yrs old and I added purèed carrot, I split my batch and added it to the part that was swirled. No issues either.
 

amd

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I've made a number of avocado, pumpkin, or carrot soaps (I actually made a carrot soap last night). The thing to remember is that the puree has to be very fine with no large chunks. My theory is that finer particles will not have room to spoil because they are exposed more to the pH of the soap. Larger particles will have less of that particle exposed to the pH, allowing it to spoil. This is my theory based on zero scientific fact. Somewhat sciency is the basic formula of soap making: base + acid = salt. Remember back in the old days people used to salt meat to preserve it. I wonder if the salt composition of soap creates a preservation system for those finer particles more than pH does.

My first avocado soap had chunks that did eventually spoil within a year (at least, that's when I found it, ew). My second avocado soap was a smoother puree with no large chunks and the last bar was 2 years old when I finally used it. Lovely soap. I need to make more.
 

cmzaha

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I put avocado in my bullet and puree it with whatever liquid I am going to use so it is pretty much liquified, I also do the same with canned pumpkin. Baby food I do not worry about pureeing further. I use baby food carrots, sweet potatoes and have used peas. I have never had any problems.
 

dixiedragon

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I've made soap with cucumber and yogurt, banana and milk and pumpkin and never had a problem with mold or fungus. Interesting question about the stuff on the outside of the bar. My thought here is that because the food items are finely pureed, the water in them becomes part of the soap, so there isn't water to support mold.
 

dndlyon

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Bacteria, mold, etc - the bugs that spoil things - need a few things to grow / survive: food, water, correct temperature, correct pH, etc.

The baddies usually don't grow in soap because the pH is too high, there's nothing nutritious for them in soap, and moisture is too low. Also, the saponification process provides a bit of a "kill step" (especially when heating is uniform throughout the bar). Between the pH drop, heat from saponification, and drying during curing - soap becomes a pretty inhospitable place for the bugs.

The typical ingredients (oils, lye, distilled water, and powdered or liquid colorants and fragrances) also don't support a lot of micro growth / survival - so the incoming micro load is low.

When you have pockets of organic material that aren't mixed well (chunks of avocado, for example), the organic material can not only bring in more bugs and provide nutrition for them, but also can create a micro-environment where moisture, lower pH, etc can allow them to grow - creating a little protective pocket of yuck that bugs love. The heat transfer rate in the chunks will also be different and may provide a bit of protection. Large particles (that contain a high moisture content) will dry slower than the surrounding soap during curing, so the extra moisture will make the bugs happy and happy bugs will make unhappy soapers.

The antimicrobial nature of soap has less to do with presence or absence of oxygen (as different bugs have different oxygen requirements - the baddest one in the food industry grows only in the absence of oxygen). And, while soap is a salt, salt is antimicrobial due in large part to it's ability to bind water (bound water isn't available for microbes to use and they dehydrate).

For all of the reasons above, and as previous posters mentioned, it's important to puree and mix well - even puree that isn't well incorporated can create islands of bug paradise ;) Strictly from a chemistry standpoint, you also want to mix well to incorporate the liquid in the puree through the soap so you have consistent saponification throughout the bar.

(I try not to science here, but I get paid to grow and kill bacteria...and I like to talk about bacteria - it's the small things that matter o_O)
 

KimT2au

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Thanks everyone, all the info and links have been great. @dndlyon your explanation was FANTASTIC, thank you so much and @amd I am off to read the article after this. I am so glad to hear that using the food stuffs is OK as every year we get a glut of something from the garden and we are still working our way through pickles from 2 years ago. Even with giving the excess away we seem to have so much of some things (and so little of others). I think this year the emphasis will be on soap rather than pickles :D
 

dndlyon

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@KimT2au - glad I could help a bit! That article is good stuff as well - thanks @amd !

I'm super jealous of your garden excess! I was too busy to plant one this year and I miss all the fresh goodness :) Would love to see a post about your Garden Line of products ;)
 
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