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How to prevent rancidity before smoke point?

Answered on August 19, 2014
Created March 19, 2013 at 11:37 PM

Commonly, when recommendations are put on to how high you can heat an oil before it reaches rancidity, smoke point is used. My question is, is there a scientific basis for this other than that at this point its DEFINITELY going rancid?

For instance, polyunsaturated oils like corn and soya have high smoke points, but go rancid at very low temperatures. Also, even if you cook with something like lard, but at a low temperature for a very long time, like, say, from unstrained bone broth cooking overnight, wouldn't the fats be damaged to some extent?

I've had several professional chefs who have told me that the pan must be hot before you put the oil in, because the oil will degrade as time goes on. I've noticed the difference in heating a pan with oil and without, and the taste is far better the less time the oil has been cooked. Also, there is a common practice of draining fat only to add it in later, leading me to believe it has to do with the oil tasting worse due to rancidity.

32f5749fa6cf7adbeb0b0b031ba82b46

(41747)

on March 20, 2013
at 01:33 AM

Not sure that normal cooking methods are going to oxidize so much to worry about, particularly whole foods. Oxidation is a problem when high PUFA oils are stripped of their antioxidants and then processed at high heat. I don't think boiling a chicken carcass is the same thing.

9f54852ea376e8e416356f547611e052

(2957)

on March 20, 2013
at 12:15 AM

This is exactly the reason why I throw away the fat from making stock. Some people save it for cooking, but fat gets rancid in higher temps and longer it is cooked - and 24 hours is a long time, even at relatively low temps when making stock.

32f5749fa6cf7adbeb0b0b031ba82b46

(41747)

on March 20, 2013
at 12:11 AM

Going rancid and burning it are different things.

32f5749fa6cf7adbeb0b0b031ba82b46

(41747)

on March 20, 2013
at 12:10 AM

@Borysewich... smoking does not mean it's rancid, only that you're literally burning it.

C07939fb80c1f445cbb5b0469d665a8e

(470)

on March 20, 2013
at 12:00 AM

Maybe I didn't word it right, I know that if its smoking, its rancid, but I wanted to know how rancid an oil could be without smoking, as well as the time and temperature it would take for this to happen. MUFA and SFA included.

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2 Answers

best answer

1
4781cf8ae1bfcb558dfb056af17bea94

(4359)

on March 20, 2013
at 02:11 AM

I agree fully with Greymouser's answer. I would add that by adding a heat-stable antioxidant you can prevent oxidation of oils. I think you can even raise the smoke point of the oil too. I think that turmeric, rosemary, and ginger all add reasonably heat-stable antioxidants.

1
Ebb10603524dd22621c1155dd7ddf106

(19150)

on March 19, 2013
at 11:53 PM

You are conflating two ideas, slightly.

First, the smoke point is when the oil starts burning. The oil gets broken down so much, the the glycerol that already was freed from the triglyceride is further broken down into smoke-y chemicals. You are beyond "rancid" at this point.

Second, heat -- and not necessarily as high as the smoke point -- speeds up oxidative rancidification. So does exposure to water, light, and chemical catalysts. Water may also introduce bacteria, which rancidify oil in their own special way.

So, to answer your question specifically: oil has definitely begun rancidification if you are seeing smoke. Even before the stove-top, PUFAs will go rancid more readily than MUFAs or SFAs are they much more susceptible to oxidization.

9f54852ea376e8e416356f547611e052

(2957)

on March 20, 2013
at 12:15 AM

This is exactly the reason why I throw away the fat from making stock. Some people save it for cooking, but fat gets rancid in higher temps and longer it is cooked - and 24 hours is a long time, even at relatively low temps when making stock.

32f5749fa6cf7adbeb0b0b031ba82b46

(41747)

on March 20, 2013
at 12:10 AM

@Borysewich... smoking does not mean it's rancid, only that you're literally burning it.

C07939fb80c1f445cbb5b0469d665a8e

(470)

on March 20, 2013
at 12:00 AM

Maybe I didn't word it right, I know that if its smoking, its rancid, but I wanted to know how rancid an oil could be without smoking, as well as the time and temperature it would take for this to happen. MUFA and SFA included.

32f5749fa6cf7adbeb0b0b031ba82b46

(41747)

on March 20, 2013
at 01:33 AM

Not sure that normal cooking methods are going to oxidize so much to worry about, particularly whole foods. Oxidation is a problem when high PUFA oils are stripped of their antioxidants and then processed at high heat. I don't think boiling a chicken carcass is the same thing.

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