Can i reuse the liquid from salting out my soap?

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B&E Homestead

May 8, 2020
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I made a 100% tallow and NaOH soap and salted it out for laundry soap and now I'm wondering what to do with the 2 gallons of water/salt/glycerine/lye mixture left over. Can i just put more fat and lye into it and cook it until it becomes more salted out soap? Or would the glycerine and salt already in the liquid interfere with the process??
If I can't reuse it to make more laundry soap, is there anything else I can do with it? Reclaim the salt out of it somehow or separate the glycerine?? I hate to have to dump it out on the ground.
Theoretically, yes, you could, but I question why the average soap maker would want to do that.

Niger (or nigre; the name for the water-glycerine-salt solution left over from salting out) contains impurities that might not be desirable in soap, including an excess of salt and an unknown amount of alkali (NaOH).

Historically, large-scale soap makers sometimes did recycle niger into a new batch of soap, but my recollection is the niger wasn't routinely recycled. I'd have to look into it more to find the pros and cons of this. Also they were using a boiled method of soap making, which is different than the HP and CP methods we small-scale soap makers normally use.

I also question why soap for laundry use needs to be salted out. I'd make the soap at a zero percent superfat -- or even a slight lye excess -- and call it good. Salting-out is a lot of work for not a lot of benefit, IMO. I do it on occasion because I like to experiment, but I wouldn't salt-out soap as a routine practice.

edit: Reclaiming crude glycerin or salt from niger is not realistic for a small-scale soap maker to do - you'll spend more time and fuel than the effort is worth. To discard niger from salting-out, I would flush it down the sink with plenty of water. The amount of salt used to salt-out a typical batch of soap isn't that big of a deal. I wouldn't water my plants with niger, but it will be fine if discarded in a septic or municipal sewer system.
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Thank you for replying. I will probably try reusing some in a small batch to see how it goes. I like experimenting too.
To answer some of your questions, salted out soap is better for laundry than just 0% superfat because there's no glycerine, or at least that's what I read somewhere. But I didn't actually set out to make salted out laundry soap. It was sort of an accident. I had a 10 year old bottle of lye that was hard as a brick and didn't know what to do with it. So I cut the packaging off with a razor knife and dissolved the whole thing in a 5 gallon bucket about half full of water. (hard well water! And yes, WAY more H2O than necessary.) It was somewhere around 30 oz of lye, but I had no way of knowing for sure, so guestimating how much tallow I would need for that much lye, I melted down 7ish lbs of home rendered tallow, (also quite old) and cooked it all in a big pot on the wood cook stove. We needed the fire that night so no wasted fuel in this experiment. The lye was otherwise worthless, and the tallow was so old I wouldn't have used it for a nice soap anyway, or for cooking. So the only thing it cost me really is the salt. I added about a pound of salt at the beginning, and after it started looking something like a HP soap in mashed potato stage, I kept adding more salt until it separated into hard soap and a brown liquid. If I could reuse the niger a couple times then I'd really feel better about having used so much salt. (My soap budget is literally $0 so...) Anyway, the soap turnout out great! I got 12 pounds of it! I have washed kitchen towels with it and even used it to do the dishes, and to my amazement, there was no soap scum. Made me wonder if some of the salt ends up in the soap instead of just in the water, and if salt works like a chelator.?? My normal bar soaps leave a lot of scum in the bathtub and I'd never try using them for laundry, certainly not dishes!
Ah, I understand now -- without any context to your question, I assumed you were making soap with a more typical CP or HP method.

Yes, some salt does end up in the soap. No, table salt (sodium chloride) is not a chelator.

"...salted out soap is better for laundry than just 0% superfat because there's no glycerine, or at least that's what I read somewhere..."

Being a chemical engineer, I'm a little skeptical about "I heard it or read it somewhere" ideas like this. There's a lot of these theories floating around in the handmade soap community that "everyone knows is true" except it turns out the theories are wrong.

I'm not saying this theory is NOT true. It's just that I don't know it IS true either. You might be right that soap without glycerin is a better laundry cleanser than soap with it, but I'd want to see some facts or testing that supports this idea before I go along with it.
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I do try to keep tabs on what is known fact vs hearsay vs my own theories... and the "better for laundry" claim was definitely just a "maybe" floating around my head with no real facts attached. So I did a quick Google search just now and turns out it might actually be good for getting out stains! Oh well. I'm not really picky about laundry so I'm sure it will be good enough for most things. I do know that soap without glycerine is not great for skin though, so I guess in that sense I could at least say it's "better for laundry soap than for hand soap!" The main reason for salting it was not to get rid of the glycerine but to make sure it wasn't lye heavy since I wasn't measuring, and because it had way too much water in it.

Thank you for your help DeeAnna. I appreciate your scientific ways.