Using old oil for soap

[welsh black]

Has anyone used old oil to make soap? Re-cycling is the big thing in the UK, and I could get an unlimited supply of used palm oil. But what would the soap be like? Would it have a smell? Would it react with the lye the same? Different SAP value? Anyone have any experience in this? Perhaps I'll try a small batch and see what happens.

 

[Lion Of Judah]

. oil that has been used needs to be cleaned before turning into soap . once cleaned you can go ahead use it to make soap no special changes that i know of in terms of SAP value nor lye . there are different methods to clean it , you just got to find the one best suited to your needs and skill level . most of them easy to do at home . re-cycling oil is big here as well but not every one is into it [ it sounds strange but its big in the green and eco friendly sector but its not in the mainstream ] so go ahead try your hand at it . keep in mind you want to see what you bar becomes over time and the characteristics it hold not just in the immediate bar you get .

 

[welsh black]

Sorry. I meant used oil, its from a restaurant !!! I'd filter it first.

 

[mintle]

I have seen similar thread on forum, with old/used oil rendering - let me check

Ok, there it is: click!

And with rancid oils, I have seen some fascinating experiment on otionsoap:
click!

I would never use any of these on my skin or my cat's skin - one of the main reasons for soap making is to know that I use carefully chosen ingredients. But for cleaning/dish washing/laundry - maybe I'd try the used oils/frying oil.

 

[welsh black]

Thanks for the link, very interesting. I like the thought of "nice" oils in my soap too, but also know there are lots of people out there who like the thought of re-cycling and "green" usage. Maybe also have used coffee grounds in the soap for gardeners soap?

 

[DeeAnna]

We use fats to make soap, because they are easily available to us. Fatty acids are not so easily available to us soapmakers, but they also could be easily used for soap making. When a recipe calls for "stearic acid", say for a shaving soap, you would be using fatty acids to make the soap.

Speaking very generally, a fat molecule is made of 3 fatty acids bound together by a glycerine molecule. When we make soap, the sodium or potassium in the lye breaks the fats into three molecules of fatty acids and one molecule of glycerin. The sodium or potassium then reacts with the fatty acids to make three molecules of soap.

Other chemicals can break a fat molecule apart, including oxygen and water. Exposure to light, heat, certain metals, and microbes can also increase the rate of breakdown.

Oxidation (the process that causes rancidity) breaks the fat molecule apart into the same 3 fatty acids and 1 glycerine molecule. If the fatty acids continue to break down further, they will eventually form smelly ketones and aldehydes. These chemicals are the source of the "rancid oil" odor. This odor will not disappear during saponification, so if the odor is objectionable, some of these smelly molecules can be removed by washing the oil with water before using the oil to make soap.

When soaping with oil that is older but still smells fine or when soaping with oil that is definitely rancid, be aware that the sodium hydroxide does not have to work very hard to saponify fatty acids, compared with the fat from which the fatty acids come. Your recipe may trace quicker than expected or the batter may rice, so be prepared for that. The lye calculation will be the same, however -- you need exactly the same amount of lye to saponify rancid oil as you would to saponify non-rancid oil.

See also this paper: Girgis, et. al, Production of high quality castile soap from high rancid olive oil, http://grasasyaceites.revistas.csic.es/index.php/grasasyaceites/article/viewFile/235/236
and this article: http://handmadesoapcoach.com/dont-throw-out-that-rancid-oil-make-soap/

 

[Bex1982]

I have seen similar thread on forum, with old/used oil rendering - let me check

Ok, there it is: click!

And with rancid oils, I have seen some fascinating experiment on otionsoap:
click!

I would never use any of these on my skin or my cat's skin - one of the main reasons for soap making is to know that I use carefully chosen ingredients. But for cleaning/dish washing/laundry - maybe I'd try the used oils/frying oil.

Dang it! I just threw out a bunch of hemp oil :???:

Oxidation (the process that causes rancidity) breaks the fat molecule apart into the same 3 fatty acids and 1 glycerine molecule. If the fatty acids continue to break down further, they will eventually form smelly ketones and aldehydes. These chemicals are the source of the "rancid oil" odor. This odor will not disappear during saponification, so if the odor is objectionable, some of these smelly molecules can be removed by washing the oil with water before using the oil to make soap.


See also this paper: Girgis, et. al, Production of high quality castile soap from high rancid olive oil, http://grasasyaceites.revistas.csic.es/index.php/grasasyaceites/article/viewFile/235/236
and this article: http://handmadesoapcoach.com/dont-throw-out-that-rancid-oil-make-soap/

How do you wash oil with water?

 

[welsh black]

After thinking about why I make my soap in the first place - nice oils on my skin, no baddies ect, I've realised my question about used oils in my soap is not a good idea!! However , I have learned a lot on the comment and links above, about the chemistry of soap making. So thank you all!!

 

[DeeAnna]

Well, basically you shake the oil with water that has some regular table salt in it -- it's not rocket science.

Here is one suggestion:
Wash your oil with a brine made of 1 part salt to 10 parts of 180 deg F (80 C) water. You should have equal parts of water to oil. Stir vigorously until it looks cloudy, then allow it to separate. Pour off the oil with a gravy separator and throw away the brine. Read more : http://www.ehow.com/how_6862730_use-rancid-oil-soap.html

Here's another:
Girgis (the guy who wrote the research paper I cited in my earlier post) washed his olive oil with a solution of water and salt. He used, if I'm reading the paper correctly, about 10% of water and 3% salt based on total oil weight. Translation -- if he had 1000 grams of oil, he washed it with 100 grams water and 30 grams of salt. He warmed the oil/water/salt mixture to 160 deg F (70 C) and agitated the mixture for about an hour.

Girgis used a lot less water and a lot more salt than the E-how procedure. So, basically, it looks like there's a fair amount of leeway in how you do it. Agitation is important to mix the water with the oil so as much of the smelly bits can be washed out as possible. I suspect, however, that you don't absolutely need the salt nor do you need to strictly maintain a warm temp, but I didn't research those points.

 

[Bubli]

I know people clean it some how then make some type of alternative fuel for vehicles, don't know as much about that topic as I SHOULD, buy couldn't you. I'm sure it would have a different odor. You could try small amounts to see.

 

[dixiedragon]

I was on an emailing list years ago and there were several soapers who regularly used cooking oil from restaurants. I believe they added some castor and some coconut oil.

Question: What benefit does the salt have when cleaning fats?

 

[dixiedragon]

I have some rancid mango butter that I am gradually using in soap. I use it at 10% (5-6% superfat) and have not noticed a bad smell or DOS. This includes the unscented batch I did that is a year old at this time.

 

[DeeAnna]

Why use salt to clean the fats, you ask? I'm not really sure. It honestly might be tradition more than science, since salt was often added when making "boiled" soap to help separate the spent lye from the soap. (I can go into the chemistry of why this works, but it's a long story unrelated to cleaning rancid fat.) People might theorize since salt is required for boiled soap, then it might be helpful for cleaning fat. Don't know. I've also heard about adding vinegar to the wash water ... again with no real explanation of why it is helpful.

One source found that "a lot" of salt in the cleaning water actually made the used bacon fat (lard) she was cleaning become progressively softer. She thought the salt was allowing some of the water to emulsify with the fat. When she washed this fat with plain hot water, the lard became harder. http://sustainablescientist.net/2013/03/04/making-bacon-soap/

IMO good mixing of the water and liquid fat is key to good cleaning. If you don't mix well, the water cannot do its job well.

Warmth will also be helpful, especially if you're cleaning a fat that is normally solid at room temperature.

Two or three washings may also be needed if there is a lot of contamination to remove -- for example, bacon grease with lots of fried bits or fat that is very smelly. The contamination may not be removed by just one washing.

Salt? Not so sure. There might well be a good reason for adding salt, but I don't know the science behind it.

 

[Bex1982]

geez, lots of work. I'd rather just use new oils.

 

[Dorymae]

I render a lot of tallow and when you render you are basically cleaning the fat. You melt it all down (with tallow you chop it first) then add water (about equal to the fat but there is no specific amount and boil the heck out of it. Then you pour it into a container and refrigerate until solid fat is on the top. Then you take the fat, discard the water and again melt the fat with clean water and boil. Refrigerate again then do the process one more time. When you are finished you have a very clean hunk of fat that you rinse in cold cold water (to clean the bottom).

At that point you can freeze, refrigerate or put it in a bucket. When it is very clean it is shelf stable.