Quick question - stale oil

I have a sweet almond oil that I did not manage to use up and it went bad. There are no oil spots or anything, but the smell tell you that the oil is bad.

So can I use the oil to make laudry soap so as not to waste it?

I wouldn't as you don't want to carry that smell over to your clean clothes. IMO.

You could try a small batch to see if the smell carries over in the soap. If it doesn't, then make laundry soap.

I personally have not done this, but, yes, technically you can.

The chemistry stuff --

We use fats to make soap, because they are easily available to us. Fatty acids are not so easily available, but they also could be used just fine for soap making.

Speaking very generally, a fat molecule is made of 3 fatty acids bound together by a glycerine molecule. Oxidation (the process that causes rancidity) gradually breaks the fat molecule apart, ultimately into 3 fatty acids and 1 glycerine molecule.

If the hydrogen that makes a fatty acid ... a fatty acid ... is replaced by sodium or potassium, the fatty acid becomes soap.

Okay, now for the more practical stuff --

The goal is to make sure absolutely none of the fatty acids remain in the finished soap. One option would be to use a zero lye discount for a CP recipe. Another, possibly more effective method might be to HP your recipe using a slight amount of extra lye, then add enough "superfat" of good oil to ensure the lye is completely used up.

Be aware that the sodium hydroxide does not have to work very hard to saponify fatty acids, compared with the fat, so your recipe may trace quicker than expected. The lye calculation will be the same, however -- you need the same amount of lye to saponify rancid oil as you would to saponify non-rancid oil.

...speaking theoretically of course...

If any rancid odor remains in the finished soap, Ruthie is right -- your clothes may smell.

I want to add another bit to this conversation.

I was reading a 1905 book on industrial soapmaking last night, and the author touched on the use of rancid oils in soap. According to the author, a rancid oil contains an excess of free fatty acids from the breakdown of the oil due to trace water and exposure to light and oxygen. A rancid oil also contains varying amounts of aldehydes and ketones, something I did not realize until last night. These chemicals are the source of that "rancid" smell.

All these chemicals have varying degrees of odor. The odor from the fatty acids will disappear during saponification, but the odor from the aldehydes and ketones will remain in the finished soap, since they do not saponify.

One of the other interesting things I gathered from this book is that an excessive amount of free fatty acids can cause ricing, especially if the ricing occurs right after the lye solution is added to the fats. The fatty acids react instantly with the lye and create the ricing effect. (Ricing from fragrances and other additives is another story.) So even if an oil doesn't smell rancid, it may still have excessive free fatty acids and may rice.

Hoegarden -- give it a try. It might work out fine, or it might not. In either case, you will learn something!

I've seen this that has a suggestion for washing rancid oil: http://www.ehow.com/how_6862730_use-rancid-oil-soap.html#page=4

I haven't tried it, so I can't say whether it works. Might be worth a try though.

I have some soap made with fresh oil and no added fragrances. Half of the batch seems to have spoiled and does smell rancid and has DOS. I did make laundry soap from it and added a fragrance oil to it (Tide FO hehehe) and it is just fine. It washes our cloths well and leaves only the fragrance that I added. I made it into a dry laundry soap just fyi.

Rachelmf said:

I've seen this that has a suggestion for washing rancid oil: http://www.ehow.com/how_6862730_use-rancid-oil-soap.html#page=4

I haven't tried it, so I can't say whether it works. Might be worth a try though.

Click to expand...

Very interesting! Almost makes me wish I had some rancid oil so I could try it. Now that I think about it, my grandma used to brine her oils before she made her "lye soap." TFS!!

I read the eHow article -- that was very interesting. Thanks for sharing, Rachelmf!

I also found a research paper (that was rather difficult to follow due to language issues) that reported on an experiment in which rancid olive oil was washed with hot brine (salt water) before making it into castile soap. According to the paper, the soap was acceptable compared to a castile made with fresh oil.

Also found this: http://handmadesoapcoach.com/dont-throw-out-that-rancid-oil-make-soap/ An excerpt: "...When you have rancid soapmaking oils don’t throw them out. Make soap and saponify at 100%. No lye discount should be taken...."

My comment -- I still think the soap could be rebatched or hot processed and a superfat of good oil added to make it more skin friendly, if you didn't want to use it for laundry.

This thread had me curious so i went googling. I found this book: Annual of Scientific Discovery: Or, Year-book of Facts in Science and Art ... Page 25 has some interesting info. One being bone char soaked for a couple days in rancid oil will make it sweet again.

You're welcome. I thought it was pretty interesting. If anyone tries it, be sure to tell us how it works!

The bone char would basically be a type of activated carbon. I certainly would think it would adsorb some of the stinky chemicals, if enough char/carbon was used.

Rachelmf said:

I've seen this that has a suggestion for washing rancid oil: http://www.ehow.com/how_6862730_use-rancid-oil-soap.html#page=4

I haven't tried it, so I can't say whether it works. Might be worth a try though.

Click to expand...

This is interesting. But what is brine the oil? I never do it before. If this is successful, I will not waste my oil.

hoegarden said:

This is interesting. But what is brine the oil? I never do it before. If this is successful, I will not waste my oil.

Click to expand...

A brine is a mixture of salt and water. These directions tell you how to make the brine (1 part salt to 10 parts water), stir it into the oil, then let it separate. I'm guessing it is OK after that process.

But how do we separate the water and the oil? put in the fridge and scrap out the oil that has harden?

The oil floats to the top and you can gently pour it off. You may lose a bit right where the oil and water meet, but you'll recover most of it.

Maybe I should try using a dropper too?

If your oil will solidify in the refrigerator, you could chill it and take the solid oil off the water that way.

Or, yes, you could use a dropper if you have only a small amount of oil to remove. If you have a large amount, a dropper would be time consuming.

Do you have a container that is tall and skinny? Especially one that is clear or translucent so you can see through it? If you do, you can pour your oil and water into that container. In a tall, skinny container, the oil layer will be easier to remove with a spoon or dropper.