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Smoke Point

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Recipes often talk about mixing oils to raise the smoke point. For example adding peanut oil to olive oil will let the mixture get hotter without smoking.

What determines smoke point? Isn't it the fats in the oil? If so, how does cutting a low smoke point fat act to raise its smoke point? As far as I can see, smoke point isn't like boiling point, where a solute will raise the BP. And it's not like mixing paint where the end product is a blend of the two colors.

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Different Oils breakdown and degrade at different temperatures and this is called their ‘smoke-point’. It is the temperature at which an oil begins to discolor, burn and turn bitter and when it chemically breaks down and decomposes. Smoke points vary slightly depending on many factors including processing. Although Smoke point degrees should be seen as good approximations only, the smoke point of an oil does decrease with each repeated heating, with contamination by salt or food particles, exposure to light and oxygen and as it thicken and darkens.

But it’s not just heat that caused oil to chemically breakdown. Time, refining, air and light are also factors.It's just a matter of time before the molecular structure of all foods break down and oil is no different. You will know when it begins to happen by the increasing rancidity due to free radical formation.

-the less refined the oil, the more flavor and color it has because of the suspended plant matter, but this also shortens its longevity. The more refined the oil the longer its shelf life but the less color and flavor it has.

-oil oxidizes when exposed to air and plant flavored oils oxidize quicker depending on the type and amount of plant matter suspended. This process can grow a bacteria called ‘clostridium botulinum,’ which can lead to botulism, therefore first cold press oils have a shorter shelf life even when stored in a closed bottle or container.

-light and air cause oil to oxidize and loose nutrients

So smoke point is affected by how old your oil is, how refined, how much it has been exposed to light and air and how much heat is applied to it.

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OK. But why should mixing oils change the smoke point? I'd predict that it wouldn't.

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I wonder if it might - working with chocolate we find that the eutectic effect of one fat on another causes the melting point to change. So it might just be that eutectics play a part in smoke points as well.

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The eutetic effect is interesting, sometimes lowering the smoke point and sometimes raising it. I don't understand the science myself despite reading the journal articles on google scholar.

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OK. But why should mixing oils change the smoke point? I'd predict that it wouldn't.

I'd predict the opposite.

If we use the information provided in TCL's post, we can easily demonstrate how this happens. if you mixed two oils that were equivalent in all properties except the number of contaminants, by adding the less contaminated oil to the more contaminated oil you would by definition decrease the number of contaminants in the more contaminated one, thus raising the smoking point. Thus if you add comparatively pure vegetable oil to butter the smoking point is raised, which is something that most cooks will tell you from observation.

Of course, if you took grapeseed oil and added butter then the smoking point would decrease but I'm assuming that we are always talking about adding a higher smoking point oil to one with a lower smoking point.


Nick Reynolds, aka "nickrey"

"The Internet is full of false information." Plato
My eG Foodblog

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interesting. this has to be something different:

if an oil smokes at Temp a and has 10parts of 'contaminants' in it, you dilute it with a second oil that has a higher smoke point, it now has 5 parts of contaminats in it. you hold it at temp a, those 5 parts will smoke, maybe 1/2 as much smoke.

so its something else?


Edited by rotuts (log)

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interesting. this has to be something different:

if an oil smokes at Temp a and has 10parts of 'contaminants' in it, you dilute it with a second oil that has a higher smoke point, it now has 5 parts of contaminats in it. you hold it at temp a, those 5 parts will smoke, maybe 1/2 as much smoke.

so its something else?

well put...and exactly my question.

I don't think melting point changing with contamination is exactly analogous to smoking. The melting point changes because there is a different, more heat stable crystal when contaminants are present. Smoke point would seem to be a different issue since presence of contaminants ought not to change the temp at which a molecule burns.

I think.


Edited by gfweb (log)

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I think that organic matter thats not 'oils' burn at a 'certain temp' more of those, more smoke at that temp. the oils themselves are a different matter, and denature at a different temp, ie 'refined' which means removal of perhaps most organic non-oils leaves the oils themselves to burn.

I dont recall reading much of this in MC Tomes, but that's a lot of pages!

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Scanning around, I came up with a statement by a graduate student in food science called Levy Pascua.

His statement was that blending oil with butter doesn't raise the smoking point of either. What happens instead is that the lower smoking temperature butter breaks down but does not smoke because the higher temperature oil acts as a solvent and thinner. Moreover, the presence of the butter with its lower smoking point oil reduces the overall cooking temperature that is required to achieve the cooking outcome.

This response seems to be half way between the two points of view without the rigidity of either. Let's hope the science supports it.


Nick Reynolds, aka "nickrey"

"The Internet is full of false information." Plato
My eG Foodblog

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I looked in MC, McGee, and about a half dozen other places today, and didn't find anything that addresses it directly. MC talks briefly about oils and their smoke points (2-123), but doesn't go into detail about what's happening.

That said, here are my thoughts on the subject: Browning butter is essentially the cooking of solids suspended in a fatty matrix. (I'm assuming that all the water is cooked off relatively quickly, and does not play any role in the browning process) the milk solids will brown, and even blacken and burn well before the fat reaches its smoke point, and are in no significant way protected from "overcooking" by the presence of the fat. Similarly, you can brown a pat of butter even when you have added a relatively large portion of peanut oil to a pan. If the solids aren't protected from burning, is there any reason to expect that a liquid-phase material would be protected? Dilution of the burning molecules may drop the threshold sensory detection, but the burned material would still be there. If this is actually the case, then it should be evident in a shorter lifespan of the oil mixture, eventual lowering of its smoke point, etc.

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This response seems to be half way between the two points of view without the rigidity of either. Let's hope the science supports it.

I'm interested in what's true. I really don't have any position in this with "rigidity".

And I certainly don't "hope" for a particular outcome.

Finding out what's true is what matters.

If one thinks about science properly there aren't winner and losers.

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I think it is important to remember that most cooking oils are highly miscible in mixture with each other and form a homogeneous solution.

This would tend to lend credence to a change in smoke point for such a mixture , because the lower smoke point oil isn't just sitting there separate from the other.

It seems to me that butter mixed with oil is a different question though, as it is a fat,water emulsion combined with an oil.

My own personal experience tells me they stay combined when cooled but I am not sure how homogeneous the mixture really is.


"Why is the rum always gone?"

Captain Jack Sparrow

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This response seems to be half way between the two points of view without the rigidity of either. Let's hope the science supports it.

I'm interested in what's true. I really don't have any position in this with "rigidity".

And I certainly don't "hope" for a particular outcome.

Finding out what's true is what matters.

If one thinks about science properly there aren't winner and losers.

Who'd have thought someone with a PhD from a Science faculty could be so muddle headed? I suppose the lack of scientific references in this topic up until now led one astray.

The experiment would be simple to conduct in a laboratory equipped to observe smoke point while applying different temperatures; unfortunately like many things that interest us in the food arena, the issue seems too trival to feature in the scientific literature.


Nick Reynolds, aka "nickrey"

"The Internet is full of false information." Plato
My eG Foodblog

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This response seems to be half way between the two points of view without the rigidity of either. Let's hope the science supports it.

I'm interested in what's true. I really don't have any position in this with "rigidity".

And I certainly don't "hope" for a particular outcome.

Finding out what's true is what matters.

If one thinks about science properly there aren't winner and losers.

Who'd have thought someone with a PhD from a Science faculty could be so muddle headed? I suppose the lack of scientific references in this topic up until now led one astray.

The experiment would be simple to conduct in a laboratory equipped to observe smoke point while applying different temperatures; unfortunately like many things that interest us in the food arena, the issue seems too trival to feature in the scientific literature.

You could probably come up with something reasonable using a deep fry thermometer and a smoke detector set a few cm above the pan. But I wouldn't be surprised if there is a time/rate-of-heating factor so smoke point isn't simply a single temperature.


It's almost never bad to feed someone.

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I keep hoping that one of the MC guys will weigh in.

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Whole butter is not a good fat to include in this discussion, because it includes water and milk solids, etc. There is nothing you can do to raise the temperature at which the milk solids will burn. This would be true of any fat that tends to "burn" at a certain temperature due to the carbonization of suspended solids, etc. These fats haven't really reached their "smoke point." The smoke point is when the fat molecules begin to break down into glycerol and free fatty acids (see: wikipedia article). Blending oils most likely has some effect on smoke point because it changes the amount of free fatty acids in the blended oil compared to either of the constituent oils by itself.


Edited by slkinsey (log)

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Whole butter is not a good fat to include in this discussion, because it includes water and milk solids, etc. There is nothing you can do to raise the temperature at which the milk solids will burn. This would be true of any fat that tends to "burn" at a certain temperature due to the carbonization of suspended solids, etc. These fats haven't really reached their "smoke point." The smoke point is when the fat molecules begin to break down into glycerol and free fatty acids (see: wikipedia article). Blending oils most likely has some effect on smoke point because it changes the amount of free fatty acids in the blended oil compared to either of the constituent oils by itself.

Don't think blending would change the amount of free fatty acids present. Each triglyceride has three of them. They do vary in chain length and saturation among the various oils though.

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Whole butter is not a good fat to include in this discussion, because it includes water and milk solids, etc. There is nothing you can do to raise the temperature at which the milk solids will burn. This would be true of any fat that tends to "burn" at a certain temperature due to the carbonization of suspended solids, etc. These fats haven't really reached their "smoke point." The smoke point is when the fat molecules begin to break down into glycerol and free fatty acids (see: wikipedia article). Blending oils most likely has some effect on smoke point because it changes the amount of free fatty acids in the blended oil compared to either of the constituent oils by itself.

That's actually exactly why I mentioned butter. Because you can't change the temperature at which the milk solids will burn, but you can dilute overall mixture by adding more oils, you can still knock back the burned flavor in the mixture. It's not butter solids "smoking" like the smoke point of oil, but it's something burning in the matrix, and salvage of that matrix by diluting with a non-burned fat. In my college chemistry class, the professor used to quip "The solution to pollution is dilution" - I'm wondering if there is a flavor equivalent at work with fats at and around their smoke points. It seems to me that something with a relatively low smoke point like olive oil is still going to burn, even if you've diluted it 10x with highly refined peanut oil. What you have managed to do with the additional oil, however, is just dilute the burned molecules.

/Edit: I'm no chemist, I'm just trying to think through this with a fairly limited tool box, and happily defer to those of you what actually know what you are talking about. I'm saying, I don't see how taking molecule A, which burns at temperature X, and surrounding it with molecules of B that burn at a higher temperature Y would actually prevent A from still burning at X. If the solution is at X+(a little) but below Y, don't you still have burned A surrounded by not-burned B?


Edited by Dexter (log)

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Don't think blending would change the amount of free fatty acids present. Each triglyceride has three of them. They do vary in chain length and saturation among the various oils though.

Each triglyceride has three fatty acids, not three free fatty acids. A free fatty acid is one that is not attached to a molecule. Different oils have a different free fatty acid content. When an oil reaches its smoke point, the triglycerides begin to break apart into glycerol and free fatty acids. An oil that already has lots of free fatty acids floating around in it has a lower smoke point than an oil that has fewer free fatty acids floating around in it. So, to make a comparison with made-up numbers, let's say we have Oil A containing 20% free fatty acids and Oil B containing 10% free fatty acids. If we combine these in equal parts, we will have Blended Oil AB containing 15% free fatty acids. Blended Oil AB should have a smoke point somewhere between the smoke points of Oil A and Oil B (although I imagine it's more complicated than simply splitting the temperature difference).


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Excellent analysis ...

but ... logically a FFA would decompose (smoke) at the same temperature point regardless of what its neighbors are doing.

we will disregard the particular bits and such.

so ...

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Lots of people seems to be assuming that particles exist independently of their medium. As a corollary, if you mix two oils, they exist independently of each other: someone said above that they are miscible which I suspect means something more than coexisting. If smoke point is a function of the level of contaminants, then diluting the number of contaminants must decrease the smoke point irregardless of the volatility of the contaminants. Subjecting something to heat in one spot is different to diffusing it across the whole. Diluting a mixture should have the same effect. Let's experiment rather than speculate.


Edited by nickrey (log)

Nick Reynolds, aka "nickrey"

"The Internet is full of false information." Plato
My eG Foodblog

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I don't follow how logically a molecule of a material will react to heat the same if in solution with something else or not. I won't claim that the blended oils have to have a changed smoke point, but it is

entirely possible. Water is a perfect example of why I don't follow the logic. Phase transition due to heat is pretty well documented for H2O yet if you add it in solution with salt those same molecules have a changed temperature for phase transitions.

Something else to think about is that surface area can affect smoke point . The boundary area with the air determines how much oxygen is available , generally a shallow wide vessel with lower the smoke point vs a deep narrow vessel.


"Why is the rum always gone?"

Captain Jack Sparrow

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Many variables indeed.

RE analogizing a solute in water raising the BP, I'd say that's a different situation than smoke point. I would imagine that smoke point is a function of the chemical structure of the oil and not much affected by what other stuff is there. A better analogy might be chips of wood and chips of plastic mixed together and heated. One will burn earlier than the other in spite of being in a mixture.

But this is all guessing.

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I'm still not sure. As contaminants seem to lower smoke point, let's do a thought experiment removing all the variables except level of contaminants.

Say we have an oil with contaminants that lower the smoke point.

Let's then add that at a 10% solution with the same oil without the contaminants.

Is the smoke point lowered by the dilution (representing 90% less contaminants), or does it still act as if it had the same level of contaminants? Let's now take that to a 5% solution or a .0001% solution. I really can't see how the smoke point remains the same.


Nick Reynolds, aka "nickrey"

"The Internet is full of false information." Plato
My eG Foodblog

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