1

I've seen many charts of Smoke Point charts for cooking oils online. And, there all slightly different if not very different. Even MasterClass and SeriousEats seems to have their own versions (butter moves around). Perhaps, that's due to the particular quality of the manufactured oil they tested, but I'm not sure.

So, a lot of cooking websites indicate that the smoke point of an oil is when the oil burns and breaks down--which chemically speaking, isn't correct from my understanding. Sure, at the smoke point, some compounds inside the oil may have broken down already since they break down at temperatures below the smoke point, but the smoke point itself is not a direct indication of that breakdown, rather, that, if any breakdown at lower temperatures should happen, it already happened when you achieve the smoke point.

So, what is the smoke point then? For me, what I've learned is that its just the vaporization temperature for oils. Water that evaporates (vaporizes) is steam. Oil that evaporates (vaporizes) is smoke (because its smokey looking). Also, I'm assuming fats and oils with the longest fatty acid chains, chemically speaking, have higher smoke points.

But, also, there's this note on Wikipedia:

"Specified smoke, fire, and flash points of any fat and oil can be misleading: they depend almost entirely upon the free fatty acid content, which increases during storage or use. The smoke point of fats and oils decreases when they are at least partially split into free fatty acids and glycerol; the glycerol portion decomposes to form acrolein, which is the major source of the smoke evolved from heated fats and oils. A partially hydrolyzed oil therefore smokes at a lower temperature than non-hydrolyzed oil. (Adapted from Gunstone, Frank, ed. Vegetable oils in food technology: composition, properties and uses. John Wiley & Sons, 2011.)"

Any thoughts?

3
  • Not an answer, but I think your point about vaporizing oil == smoke isn’t accurate. I’ve a vague recollection of seeing a boiling point for an oil that was markedly different from the smoke point Oct 6, 2023 at 15:31
  • en.wikipedia.org/wiki/Smoke_point Not sure but that's what I also recall from my chemistry days. I think the main thing to discern here is: At smoke point, does the oil (substance that mainly consists of a carboxylic acid with a long hydrocarbon chain from the alpha-carbon (i.e., a fatty acid) break down (irreversibly)? Another question to guide us would be this: Can, you re-condense the oil in a container if you catch the "smoke"? I think so. I've seen oil condense on range hoods and range hood have apparatuses for catching oil. Oct 6, 2023 at 17:03
  • Triglyericdes (in fats) are a different beast. Those may break down. If significant acroilin evolves from oil, its not an oil as there's significant amounts of glyercol. Honestly, great subtopic tho. Oct 6, 2023 at 17:03

1 Answer 1

6

Smoke and vapor are not the same thing.

The process of something smoking is a form of thermal decomposition called pyrolysis where heat acts as a catalyst for something to chemically change into something else. For instance, if you press wood against a hot surface, it will start to smoke and char even without bursting into flame, and that's because the heat is causing the chemical compounds in the wood to degrade into different compounds. Food being cooked will do the same thing in a hot pan or oven - eventually, it will burn, releasing smoke and leaving behind a lump of glorified charcoal. The smoke is composed of the components that are vaporized (such as water), gaseous (such as CO2), or exist as tiny particles that are buoyant in the hot air (i.e. ash), and the char is the stuff that's left behind.

Vapor, on the other hand, is a product of the process of evaporation. How this process works on a technical level can get complicated, but the grossly oversimplified explanation is that a material has entered a phase in which it is both light enough to be buoyant in air and energetic enough to no longer be stably connected to other nearby molecules. Boiling is the widely known way a substance can evaporate, but it's not the only one; some substances are energetic enough on their own to just leech directly into the air given enough time. For instance, if you leave a glass of water out at room temperature, the water will eventually entirely disappear, though how long it will take depends on the temperature and humidity of the environment.

When oil reaches its smoke point, it is not boiling, it is decomposing. This is because while it's technically possible for oil to boil, the boiling point is higher than its smoke point. The reason for this is that the molecular bonds in oil are so strong that the amount of energy required to break them and cause the oil to boil off is higher than the amount of energy to get the oil to start decomposing into something else entirely.

Now it's possible for trace amounts of oil to start vaporizing during the cooking process, hence why range hoods over stoves and griddles can get pretty oily over time. But as mentioned before, boiling is just one way a substance can vaporize - just because the oil is vaporizing doesn't mean it's boiling. Theoretically, yes, this oil can be captured and reused, but its in such low quantities that it's hardly worth the effort. And besides, oil isn't the only thing condensing on those range hoods; the smoke is condensing on those surfaces too, and when smoke condenses, it forms tar.

6
  • 2
    Great answer by Abion47. Off the top of my head, I would add that this feature of oils is also somewhat analogous to that of sugar. If I am not mistaken there’s also a thing about sugar decomposing into carbon and water at a temperature that’s lower than it’s boiling point. So you will never really get to boil sugar. Oct 7, 2023 at 3:03
  • Great answer, and thank you for your time. I think there should be a distinctions and connections made between these terms: Vaporization point Smoke point/Burning point Fire Point/Combustion point Flash point Also, as addressed previously, as been referenced previously, acrolin evolves following decomposition of gylcerol from trigylcerides. However, many oils are not trygylcerides, but fatty acids/FFA. So, if fatty acids must decomposed, just as someone else suggested here, it would be via pyrolysis, which would require splitting of C bonds, which requires a lot of energy... Oct 14, 2023 at 1:18
  • Also, "Smoke point" seems to reference a macroscopically observable phenomon of "smoking". Impurities in cooking oils that may contain substances that may undero pyrolysis readily may also exist. And, Wikipedia point this out as well, referencing "blue smoke" but no physicochemical mechanism. So, for me, its hard to discern still despite your great answer. Thanks again. Oct 14, 2023 at 1:20
  • Also on your point where you say this: " But as mentioned before, boiling is just one way a substance can vaporize - just because the oil is vaporizing doesn't mean it's boiling."... So, you do understand my point here as I did allude to the observed phenonom of oil collecting on range hood surfaces and even devices that collect said oil (drip pan apparatuses). Since you also likely are a technical person, the distinction of between boiling and vaporization matters. However, I was careful not to mention boiling in my initial post so I'm focused on vaporization here. Oct 14, 2023 at 1:23
  • 1
    @PettyCashPrash At the end of the day, the distinction between smoke and vapor is simply that smoke is a product of decomposition and vapor is a product of evaporation. The end result may look similar visually, but the physical/chemical processes that happened to get there are completely different. Granted, this is greatly confuddled by sources around the internet who, in their cooking-centric views rather than scientific views, use these and other related terms rather arbitrarily and interchangeably.
    – Abion47
    Oct 14, 2023 at 14:44

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.