How NOT to wash your oil

Rancid oil, hooray! I took it as an opportunity to try out the oil brining technique to freshen it up. That means mix the oil with a 3% NaCl solution for a while then let it settle out.

If you do this, do not shake! Don't do it!

I was in a hurry so I figured it would go faster if I shook the stuff up a few times before leaving the workshop and let it settle overnight.

Fast forward 24 hours and I had most of the water on the bottom and an unbreakable emulsion of brine cloudiness on top.

Strike one. Gotta wait for more oil to go bad and try again.

How does that work? What does the salt do to freshen the oil?

Maybe I should back up. What's happening exactly when an oil goes rancid? I know it has something to do with oxidation, but I'm not sure I really understand what that means.

JBot said:

How does that work? What does the salt do to freshen the oil?

Maybe I should back up. What's happening exactly when an oil goes rancid? I know it has something to do with oxidation, but I'm not sure I really understand what that means.

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In broad strokes, rancidity is the degradation of the oil resulting from certain chemical processes, most notably hydrolysis and oxidation.

Hydrolysis is a reaction that a triglyceride undergoes with water to yield a glycerin molecule and three free fatty acids. This is what happens:

http://www.biotopics.co.uk/as/lipidhydrolysis.html

Oxidation refers to the double bonds of unsaturated fatty acids being attacked by oxygen. This produces smelly compounds called aldehydes and ketones. These reactions can be catalyzed by trace metals, which is why we're careful about the racks we cure on and why chelating agents like EDTA can be helpful. Antioxidants like BHT also fight this sort of rancidification.

So, rancidity has effects on the flavor, odor, color and pH of the oil.

Brining involves adding a 3% sodium chloride solution to the oil at 180 F. Mix for a period of time, allow to settle, then decant the oil off the top. What little info I've seen indicates that this has positive effects on several quantitative measures of rancidity.

The only thing I know about WHY this works is that it should definitely remove some quantity of free fatty acids from the oil. Those are the least of our worries for soaping purposes (they cause acceleration but otherwise just turn into soap), but apparently there are other improvements to the condition of the oil. I'd like to know more about why.

Have I mentioned, if you try this, not to shake the oil and water? Do not shake. ;-)

This happened to me with my rancid cooking oils however, I was able to get it much clearer and removed most of the emulsion to the point where it was useable.

To do this, I washed it with clean (no salt) water multiple times. Try using a beverage dispenser if you can find one, this way you can just pour off the bottom layer (it serves as a crude sepratory funnel). Like this one: http://www.amazon.com/dp/B005S4LOYY/?tag=skimlinks_replacement-20

I washed it with hot (160 F) water a few times. Then when it cooled back to room temperature, it was translucent and not an opaque emulsion. The emulsion did not clear 100% but I felt it was good enough to use in soap.

ETA: My oil was not necessarily rancid however, it was used for some stinky cooking and had some solids. This method left me with oil that smelled mostly of fried potatoes instead of the fried fish smell (Ewww).


I also used all 5.6 pounds right away to make soap. You can see my post here: http://www.soapmakingforum.com/showthread.php?t=53473

topofmurrayhill said:

Oxidation refers to the double bonds of unsaturated fatty acids being attacked by oxygen. This produces smelly compounds called aldehydes and ketones. These reactions can be catalyzed by trace metals, which is why we're careful about the racks we cure on and why chelating agents like EDTA can be helpful. Antioxidants like BHT also fight this sort of rancidification.

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Wow. Who needs poetry?! Be still my heart!

(I could pretend to be joking, but I'm afraid that I really am that nerdy.)