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.
asked byBorysewich (470)
Get FREE instant access to our Paleo For Beginners Guide & 15 FREE Recipes!
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.
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.