carebear said:
Used cooking oils are well on their way to rancidity, so you'd be risking early DOS. If it's just for yourself and you are certain that no cleaning fluids went in there, then try it. But I'd personally not sell it or even give it away.
Used cooking oil is recycled into many things including pet food and candles.
It is not "well on their way to rancidity" unless they sit in the pressence of water. Dry oils rarely go rancid, even when sitting for a very long time. Also, even rancid oils can be cleaned. Cooking oil usually only goes rancid if it sits outside for a long time in a drum or dumpster that's not properly covered.
As for it developing DOS early, all pure soy bar will eventually do this. I'm not sure that virgin Vs. used makes any difference but I'll admit I haven't timed it. There are many ways to prevent it from doing so... but I'm not tellin' how 8)
I've also made many observations on DOS and I'm still not sure what it is but I'm skeptical that it's rancidity. It doesn't smell and doesn't develop colonies (as is evident by a lack of speckles). It does however have the same properties as the glycerin that can precipitate out of pure biodiesel glycerin soap. I'm hoping I can get a university to send a sample to get checked on a gas chromatograph so I can know for sure... either that or run a culture on it.
You are right about the cleaners but most restaurants don't mix oil with cleaners, they clean the fryer when it's empty. And if you ask them not to, they probably won't.
I've been working with used cooking oil for years and have gone through thousands of gallons of it. And though I only took Chem1 in college, I've also been asked to speak at several universities including Chemical Engineering departments about used cooking oil and its benificial uses.