My procedure for salting out

Four years ago I posted a question here about salting out soap, which was received with some confusion. I now have reached the point where I have mastered salting out to my own satisfaction. I will describe my procedure, not because I think it original or in any way better than any other, but because I could find no such procedure anywhere, and my experiences might help another person who finds himself with a similar problem.

Caveat: I make functional bath soap, NOT suitable for milady's boudoir. It is plain lye soap, yellow to tan in color, made from whatever oil or grease I can come up with. Nonetheless, my objective it to make it (nearly) colorless and odorless, a real challenge when starting with such "crude" oil. When I make soap from relatively clean oil, I shoot for 5% superfat -- so there is no excess lye in the soap. However, when I plan from the start to purify the soap by salting out, I use excess lye -- which will be washed away in the salting-out step.

My latest batch of soap was a real success, not because the result was exceptional, but because the starting oil (used cooking oil saved, apparently, to make biodiesel!) was about the color of motor oil, and smelled rather bad. I cleaned this oil as much as possible by straining through cloth, boiling it up with water and letting it separate, but the resulting water contained little in the way of impurities, so further refining the oil was not going to help.

Therefore, I saponified the entire lot (~13 lbs) using a slight excess of lye, and following the usual sort of procedure. I cook my soap hot -- 150F or so -- which I can get away with because I use no additives in it. As a result, the soap forms in minutes and requires little or no curing. I did my first salting out right away merely by adding two or three liters extra water, and, when that was mixed in, an excess of salt. After boiling this up -- mainly to mix it -- I let it cool outside a couple days (till I could get back to it).

When cool, I dug through the hardened soap and found that the brine was nearly black, and had gelled like aspic -- something I'd never seen before when soap making. After washing away this ugly gel, I added about 3L of water to the pot and heated it up, breaking up the mass of soap by slicing it, mashing it, and running it through a 1/4" hardware-cloth strainer. (This mechanical work was needed because the soap had hardened as it cooled. I learned from this, and in the future will transfer the soap off the brine before the soap fully cools and sets up.)

When the hot soft soap was homogeneous, I added about 1 kg of salt to saturate the water, and continued heating and stirring until the soap floated atop the brine. I then transferred the soap to another container, leaving the nearly black brine behind, and repeated the salting out by the same procedure. (See bottom.) The final brine was only dark amber, and I judged that clean enough for me, especially since the odor was gone.

I ladled the soap into rectangular plastic containers to a depth of about 2.5", covered them and let it set up overnight. In the morning, I sliced it into bars, which I set on toweling to dry further. This procedure yielded over 50 bars of soap, roughly 1" x 2.5" x 3.5" -- a convenient size for the bath.

My question of four years ago pertained to the soap not sticking together when salted out. This problem has never occurred to me again. I find the hot, salted-out soap behaves very nicely. But perhaps a better description of my salting out process is warranted. The following is based upon my understanding and observations:

Soap mixes infinitely with water, but not with brine. Therefore, my procedure is to add a moderate amount of water to the soap mix (3L worked well for this batch that started with 13 lbs oil), and heat and mix till the water and the soap are homogeneous -- soft soap. To remove the excess water, I use enough salt to saturate the water present -- roughly 350 g salt per liter of water. (No, that's not exactly correct, but it doesn't matter. This isn't rocket science.)

Since I use rock salt, it takes a little while to dissolve, but as it does, the creamy soft soap starts to separate into a somewhat denser hot soap, while the brine tends to settle to the bottom. When the salt is mostly dissolved, I let the mass settle out. At this point, there will be some brine still mixed with the soap, but that doesn't matter.

As I learned, the time to judge the purity is before the mass cools completely and the soap hardens. Pull some brine from the bottom. I judge the brine by color. If it's dark, you might want to repeat the salting out. To do this, ladle the soap into another container, throw out the brine, and repeat the salting out by first adding water to the soap, then adding salt to the soft soap. Repeat until you're satisfied -- it only cost you a little water, salt, fuel, and time.

Thank you for sharing this in depth procedure. Do you always make soap in this manner or were you just trying to find a procedure for salting out, as you called it?

I commend you for having the patience to work this process out. Seems complicated. This is the first I've ever heard of such a process. It is interesting, though. Thanks for sharing.

Wow! Thanks for sharing your experiences and process. Is your purpose to be able to use old oil like used cooking oil so it's not wasted?

So, what is the purpose of salting out the soap? Is it so your can remove impurities from used oil to soap with it? That's a very in depth procedure that I think is "beyond my scope of practice"...though I can appreciate reusing oil that would otherwise be thrown out. Would this method work with rancid oils or DOS afflicted soaps? Or am I way off track with the purpose of salting out soap?

This information is not really for you because it looks like you have done you R+D really well. For others that are interested this is the like old fashioned boiled soap. There are a lot of ebooks from the 1800s and early 1900s about soap making that you can down load that describes the different ways they used to make soap. Including some on transparent soaps, liquid soaps and usually all books have at least a small part on cold process. They also talk about tasting for zap, yellow spots occurring on aging when certain oils are used and good description of the milling process for those of you that call remelting hand milled. Lots of good info.

Thanks for sharing all your hard work and your process with us. Very informative. Sissy

I'm following up on my (top) posting with a detail I didn't fully realize and didn't report: Use soft water for the salting-out process!!! Some years ago I posted on a failure of salting out, and I've since had one more such failure. The problem, I'm convinced, was that in both cases I had used too much hard water.

Soap is the sodium (or potassium) salt of fatty acids (plus a minority of other stuff, perhaps), and is completely soluble in water. But hard water contains calcium and magnesium salts (and possibly iron and others), the "soaps" of which are insoluble in water. Bummer. Using too much hard water turns your batch of salt into a batch of "bathtub ring"!

To prevent this, use either soft water (from a water softener that uses "water softener salt") or just use distilled water (from a dehumidifier). I do the latter because I don't have a water softener, and I'd throw away the condensate from the dehumidifier anyway.

Using distilled water, I am now able to salt out a batch of soap repeatedly, washing away water-soluble impurities each time, and reducing the odor. This is not a 100% effective procedure. The soap from the nasty oil I have been working with still has an odor and a distinct (though not necessarily unpleasant) yellow color.

In my latest go-around, I've done one final salting out, which left a medium-amber-colored brine (as opposed to dark amber or black), and now I'm doing one final brine "rinse" of the batch, and that will be it. I can still smell the bad odor in this soap (derived directly from the nasty oil it was made from) and I rather doubt it will be suitable for the bath.

Bottom line: Salting out is a very useful technique in some instances, especially for correcting an "oops" in which you used too much lye, but will not take a really foul soap and turn it into a lovely, clean-smelling white soap! Start with "clean" oil and fat to get clean soap. Use salting out as a "tool" along the way.

Now, to respond to some questions above (which I saw today for the first time):

Q: Do you always make soap in this manner or were you just trying to find a procedure for salting out, as you called it?

A: I certainly don't ever plan ahead on using salting out in my soapmaking, but I do make soap from my waste cooking oil, and salting out is a way of removing the dark color from such soap, should it happen that refining the oil before soapmaking didn't do the trick.

Q: So, what is the purpose of salting out the soap? Is it so your can remove impurities from used oil to soap with it?

A: Succinctly, salting out allows you to separate the soap from water-soluble impurities, such as odors or colors. I consider it a means of save an otherwise failed batch. I consider it much more important to refine the oil before soapmaking. (I refine the oil by running it through a fine strainer, then boiling it up with water and letting it cool to 40F or so, possibly multiple times, and discarding the water.)

Q: Would this method work with rancid oils or DOS afflicted soaps? Or am I way off track with the purpose of salting out soap?

A: Please avoid acronyms like "DOS" - "Dreaded orange spots". (It took me a while even to learn what it means, from www.natural-soapmaking.net/DOS.html). Salting out would probably correct the spots, but it would probably work only moderately well for removing the odors of rancidity. However, I simply don't understand how soap can go rancid and SMELL unless it is very significantly overfatted with unsaturated oils. Soap is a salt, and hence is of very low volatility. I would think that only the free fatty acids could give rise to an odor. In any event, this was not MY purpose for salting out. I see it as a means for eliminating excess lye if you muck up the recipe, or excess color if you're working (as I do) with waste oil.

You are a more persistent person than I! I thank you for sharing the process but I don't think I'd attempt it unless the world order collapsed and I had no other option. Too time-consuming for me and not without it's own added water and energy costs. Reminds me a bit of the messiness and repeated melting and rinsing involved in rendering tallow from game fat.

Sorry about the acronyms but DOS is so prevalent among soapmakers that it's generally not translated. When I googled DOS and soap, I came up with multiple hits in a second or two.

Personally, I have to superfat at at least 7-8% or the soap is too drying for my skin. However, if I use stable oils with a long shelf life and keep my rinoleic and rinolenic numbers low, the soap is used up long before it has a chance to oxidize or smell bad.

There is also a handy acronym thread stickied, for quick reference.

Sounds like an interesting process. If you have time at some point, I'd love to see it in pictures, too.

If I'm not mistaken, this sounds similar to the common commercial process for making soap. Very interesting. I never heard of anyone endeavoring to do it at home. Kudos!

Unfortunately the glycerine produced by saponification of the triglycerides will end up in your brine phase, which you discard. One of the benefits of handmade soap (by the normal CP or HP method) is that the beneficial glycerine remains in the soap.

True, but if marginal fats that would otherwise be wasted can be converted into useful soap, I'd say making "boiled soap" on a small scale like this has more benefits than disadvantages. You don't have to know the exact saponification value for the fat blend -- just make a good estimate of the required lye and adjust at the end of the saponification process as needed. This soap could be used to make laundry powder, if the lack of glycerine in this soap is an issue for bath use.

I've never quite understood the rationale for worrying about glycerine in soap. Glycerine is a natural byproduct of saponification of triglycerides, so it ends up in soap, but I don't follow how it's a benefit. It's touted as being beneficial to the skin, but I've tried using pure glycerin and all that happens is my hands end up tasting sweet! To each his own...

Anyway, this is another follow-up to my salting out. I packed the soap "curds" into my Tupperware containers and let it set up a bit (a physical, not a chemical process), then cut them out. They're a bit damp, so I'm letting them dry, which also brings a salt "florescence" to the surface (easily washed away with first use).

I've been using one of these bars for handwashing and I'm pleased to report that the odor is no longer objectionalble. Again, not for lady's boudoir, but fine for rough work. I'm thinking of milling them and adding a scent, but that's for another thread.

i have never make soap using used oils, though i would love to, as we have quite a lot in here daily. rather than going to the bin, why not use them one more time, right? i'm thinking, laundry soap

i dont think i'll have the patience like you did for the salting out process, though

edited: i dont think i will go thru with the idea of using used cooking oil for laundry soap. i took a peek at the used oil today and it was pretty yucky, all black with small bits of fried whatever floating. and since i dont have the patience for salting out, the plan is going out the window

Glycerine is a humectant. In soap, or lotions, it moisturizes the skin, helps prevent drying out of the skin, and due to being a humectant actually attracts moisture to the skin. Used completely alone it is quite viscous and sticky, but would have the same moisturizing benefits to skin and hair. Much more pleasant when introduced to the skin by soap or lotion.

I found this whole thread interesting. It reminded me of something I read on how to salvage rancid oils and be able to use them for soapmaking. I was able to try it tonight, as some cheap coconut oil I got last week turned out to be rancid, and was brown and smelled like burnt popcorn. Eww. (I got a refund on it, but they didn't want the rancid oil back)

I was going to throw it away, but I thought about this thread on cleaning oils, and about the article I had read, so I figured, at worst, I still throw it out, at best, I make 2lbs of 100% coconut oil soap with 0%SF, and shred it for laundry soap.

The method I read in the article was to use an equal amount of boiling water as the amount if oil you have, and dissolve salt in it at a rate of 1 part salt to 10 parts water. I actually used about 1.5c salt in 32oz boiling water. Just seemed right. Mix the oil and water until cloudy-ish and well agitated, then let it all settle. When it's separated, carefully skim off the oil -- I used a gravy separator -- and discard the brine.

OMG it worked. The oil turned clear unscented yellow instead of stinky brown. And was white once it cooled all the way. I was amazed.

And I made soap of course.

I guess I'll be shredding it for the next few days, then will have probably a years supply of laundry soap.

Nicely done, Grayceworks! I'm filing your tip in my stash of good info for future reference.

Gracyworks - If I read your post right, you were cleaning up rancid OIL with boiling brine. That's not the same as the salting-out I was speaking of, but it sounds like an excellent trick to add to my bag. Thanks for posting.
For some time now I've been considering re-acidifying a bar of this smelly soap -- which would convert it to (impure) stearic acid. That alone should get rid of some more impurities in the soap. But then I could use your boiling-brine wash to reduce them further, before re-saponifying the steric acid back to soap. Obviously, this is not an economical approach to soap-making, but I'm curious how it would work.

I would think it should also work for cleaning up used oils BEFORE making the soap, to help remove the impurities and cooking odors, to lessen or eliminate the need for the extensive salting-out process. I probably won't get an opportunity to try this however, as we rarely have leftover cooking oils, we generally use just enough to prevent food sticking, no frying or anything that would require larger amounts of oil.

"... Obviously, this is not an economical approach to soap-making..."

Actually, it can be economically viable if you make soap on an industrial scale, but I agree with your point of view for a small-scale or hobby soap maker. A lot of work for small return. But interesting, nevertheless.

grayceworks said:

I would think it should also work for cleaning up used oils BEFORE making the soap, to help remove the impurities and cooking odors, to lessen or eliminate the need for the extensive salting-out process. I probably won't get an opportunity to try this however, as we rarely have leftover cooking oils, we generally use just enough to prevent food sticking, no frying or anything that would require larger amounts of oil.

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Actually you nailed it. Clean oil, no black or amber colored oil.
Plus the OP said the salting is to address excess lye so I would think
if anything this part of the process if using dirty oil would be helpful.