You know the saying: Where there’s smoke, there’s fire. But in cooking, that’s not always the case. Sometimes there’s just hot oil.
All fats, including the oils you typically use in the kitchen, have a smoke point, the point at which they will begin to produce smoke. Specifically, it’s when anything in the oil — fats, proteins, sugars, other organic material — starts to interact with oxygen and burn, says Joseph Provost, a chemistry and biochemistry professor at the University of San Diego who co-wrote “The Science of Cooking: Understanding the Biology and Chemistry Behind Food and Cooking.”
On a practical level, oil that’s heated past its smoke point can be problematic for a few reasons. It makes your food taste and smell bad, the smoke detector could go off and you may end up with a bear of a mess to clean up on your skillet.
I say skillet (or pot or other piece of equipment used on your stove top) because the most likely situation in which you hit the smoke point will be when you’re applying direct heat to the oil. That also applies to deep frying. We’ve consistently heard from readers chiding us for recommending roasting food with olive oil in the oven at a temperature above the supposed smoke point (depending on the variety, anywhere from 280 to 400 F), but there’s more at play here. In an oven, Provost says, there are plenty of other things to absorb the heat and energy — the pan, the food, the moisture of the meat or vegetables. Water or a sauce with the food can help, too. The oil is not taking the brunt of the heat, and it’s unlikely that the temperature of the oil will equalize to that of the oven itself. If it did, your food would probably be dried out and inedible anyway.
Even when it comes to stove top cooking, there’s less to be worried about than you might think. “But except for the lowest-smoke-point cooking fat of all, unclarified butter, which begins to smoke at only 250-300 degrees, smoke shouldn’t be a problem in sauteing and pan-frying unless you have a very heavy hand on the burner control,” food scientist and author Robert Wolke explained in the Washington Post in 1999. Some recipes, such as for searing meat and stir-fries, may even instruct you to wait to cook until you see a faint wisp of smoke wafting off the oil.
Despite the many smoke point charts and guides out there, Wolke was wary of assigning specific temperatures to specific oils. “Exact smoke-point temperatures cannot be given because a particular type of oil can vary quite a bit, depending on its level of refinement, the seed variety, and even the climate and weather during the plant’s growing season,” he wrote. Still in 2007, he wrote, “for those of you who insist, here are ballpark smoke points of some common refined cooking oils”:
- Canola, 400 F
- Cottonseed, 420
- Sunflower, 440
- Corn, 450
- Peanut, 450
- Olive pomace, 460
- Soy, 460
- Extra-light olive, 468
- Safflower, 510
Are you going to actually be able to measure the temperature of the oil? Unless you’re deep-frying and employing a thermometer, the answer is probably no. You’re going to see or smell the smoke instead.
What’s important to think about is how refined the oil is. Virgin or raw oils have lots of compounds that contribute flavor and aroma, Provost says, but they tend to burn. As they’re refined, those compounds fall out. That raises the smoke point, but “as you purify and refine, you lose flavor,” he says. So extra-virgin olive oil — aromatic, flavorful — has a much lower smoke point than something like an odorless, flavorless refined vegetable oil, which might include corn, canola and sunflower oils. However, the smoke point of oils, even those higher vegetable ones, decreases as a result of cooking. So keep that in mind if you’re someone who reuses frying oil, and discard the oil after a few frying sessions.
It’s also helpful to know that animal-based fats such as butter and lard generally have lower smoke points than vegetable-based options. In the case of butter, clarifying it, as with ghee, can help boost the smoke point by removing the burn-prone milk solids.
Provost says the biggest determinant of smoke point is the amount of proteins and free fatty acids. The more there are, the lower the smoke point. Oils with more polyunsaturated fats, such as regular safflower or canola oil, will have a lower smoke point. At the middle would be those higher in monounsaturated fats, such as avocado and nut oils. The higher the saturated fat and monounsaturated blends, the higher the smoke point. Think palm oil and refined coconut oil.
As to the health implications of cooking oils to high temperatures, Provost explains one byproduct that can be present in the smoke is acrolein. It can bind to amino acids and DNA in your body and cause changes in the DNA, making it a potential carcinogen. Provost emphasizes that the concentration and the duration of the exposure is what’s key, so if you’re a line cook burning a lot of food and then inhaling the smoke, it could be an issue. For home cooks who generate a little smoke now and then, “you’re not going to hit the point where it’s going to be toxic,” he says.
Much has been made about how breaking down oils while cooking can create free radicals, compounds that form slowly at room temperature and faster at higher temperatures. Provost says free radicals themselves are not the direct problem and eating them is unlikely to affect you, though they can attack flavor and aroma molecules and beneficial compounds in the vitamin E category.
Most of the time, a little smoke or burned food is the biggest problem we face when flirting with the smoke point. As temperatures creep higher, though, you run the risk of reaching the flash point, at which gases can ignite in the presence of an open flame, or the fire point, at which the oils themselves can spontaneously catch fire. But those are very unlikely, at around 600 and 700 F, respectively, Wolke explained.
Especially under high direct heat, just make sure your oil of choice can handle your cooking method. For most moderate cooking, though, don’t be afraid to let flavor and price — do you really want to deep fry with expensive olive oil anyway? — guide your decision.