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As an example, we often lightly fry onions in (preferably) Olive Oil before adding them to any number of dishes, such as scrambled eggs for breakfast.

My talented cooking friends frequently remind me, "Don't put your veggies into the frying pan until the oil is hot!" The thing is, I personally can't tell the difference if I put my veggies in immediately after adding oil to the pan, or if I wait for the oil to properly heat up first. My friends also tell me, "Don't turn the heat up all the way either!"

  • Why do people recommend heating the oil first? Are there really benefits to waiting the 3-5 minutes?

  • If the answer to above is yes, how high should you turn the heat up to get the oil? Can I just set it to 100% for 1 minute to cook the oil faster? Yes I realize I have to watch the oil carefully otherwise chaos will ensue.

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  • If you turn your heat all the way up, you also heat the pan at that speed, which is important to remember.
    – justkt
    Dec 22, 2010 at 18:45
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    First heat the pan. Even if you walk away for a while, nothing happens because you haven't put the oil in yet. But don't turn the heat up full because then when you finally put in the oil it will start to smoke really fast.
    – BaffledCook
    Dec 22, 2010 at 18:55
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    Onions are a special case, as often you want to let them cook on a low heat for the effect that causes, see sweating in the answers. Most vegetables you would not want that to happen.
    – Orbling
    Dec 22, 2010 at 19:14

5 Answers 5

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If you are looking to fry veggies then yes, it is necessary to pre-heat. If you put them in a cold pan with oil, you start 'sweating' the veggies instead of frying them.

For example: if you put a sliced onion into a pan with hot oil, it will cook and have a nice golden brown color as it caramelizes. Put that same sliced onion in a cold pan with cold oil and then add heat, and the onion will first turn translucent and lose moisture.

Both of these cooking methods have their uses, but they are different.
How do you know when the oil is ready to cook? It will start to shimmer a little before it reaches the smoking point. Put the veggies in when you see this shimmer, or at the very first wisp of smoke.

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    Technically the definition of sweating is not that you don't pre-heat the oil. It's just the low temperature. Or, to quote Michael "Sweating onions....just means to cook them until they are translucent and giving up liquid, over a low enough heat that they don't caramelize." Pre-heating oil is irrelevant.
    – justkt
    Dec 22, 2010 at 18:44
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    If you are frying/sauteeing vegetables, they will sizzle and pop, and begin to brown around the edges. At lower temperatures, they will still cook (and bubble a bit), but not brown, as they are essentially steaming in their juice.
    – Bob
    Dec 22, 2010 at 18:50
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    Visible smoke with some types of cooking oil means you heated the pan to what is beyond specifications of most nonstick coatings...
    – rackandboneman
    May 14, 2018 at 8:28
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You heat up the oil first because your food tastes/feels less greasy oil is hot (around 350 degrees F) than when it is cold (under 300 degrees F). So if you want your food to resemble the greasy food of your iconic dive-y restaurant there is, I guess, no need to heat your oil. Otherwise, do heat it. You usually want it hot enough that if you toss a few drops of water in there, they sizzle.

As to how high to turn up the burner when heating, usually most recipes that I've worked with suggest medium-high for many applications, except perhaps searing steak. When working with olive oil specifically you don't want the temperature to go too high because olive oil has a low smoke point. Depending on how refined the olive oil, the smoke point can be as low as 374 degrees F (reference). You don't want to heat oils past their smoke point, because they begin to break down at that point. In order to avoid doing so, I wouldn't heat at 100%.

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    Incorrect. Food will absorb more oil at higher temperatures. seriouseats.com/2010/10/the-food-labs-top-6-food-myths.html
    – Bob
    Dec 22, 2010 at 18:46
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    @Bob - thanks for catching my sloppy phrasing. From the article you linked, however, I point out "There's no denying that frying food at a low temperature—say below 300°F or so—leads to greasy end results, and that upping the temp to 350°F or above will infinitely improve your food's crispness." If the difference is no pre-heating versus heating, it still matters (even if only from a taste perspective). I will edit.
    – justkt
    Dec 22, 2010 at 18:52
  • Also, @Bob, having seen the idea that food soaks up too-cold oil in Cooking Light, and the sentence I quoted, I might have to do some more digging into the science of it.
    – justkt
    Dec 22, 2010 at 18:56
  • There's definitely some controversy, though I think the key point is that hotter oil will make make for a crispier result, regardless of the amount of oil absorbed. There also may be multiple types of oil absorption happening, like oil absorbed into the food vs oil clinging to the outer surface.
    – Bob
    Dec 22, 2010 at 19:00
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To sauté, the dry pan should be brought to a medium/medium-high temperature. At the correct temperature, if you drop a spoonful of water into the pan, it should form a single solid mercury-like ball that glides across the surface. Once the pan is heated, the oil can be added. The oil will come to temperature in a trivially short period of time.

To heat the pan, it's best to set the heat at the point you want it, and allow the pan to come to that temperature, instead of setting the heat very high, as this will risk overheating the pan.

For sautéing, use an oil with a high smoke-point, I prefer grapeseed oil because it retains its health benefits even when cooked at a high temperature, unlike say, olive oil.

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My chef busts of me for this but in my opinion it’s actually more efficient... I will have a stack of sauté pans in the back left burner of my station and I keep the burner on low. Say I need to sauté asparagus, I’ll grab the lowest pan which is ripping hot with my tongs, add the asparagus and then drizzle oil over it. The oil shoots up in temperature quickly enough to start frying immediately, then I’ll add my garlic to sauté immediately after and then hit them with veg stock. You don’t have to wait for your oil to get hot and then drop veg and splash hot oil or burn yourself. But your pan has to be super hot in order to do this properly. It’s faster and easier.

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First answer is yes, it matters, sometimes. Food reacts differently to different temperatures, particularly when you're aiming for certain coloring. The type of metal pan you're using also reacts differently to oil and heat so as to stick or not stick. The most important reason you keep your oil hot is in a restaurant environment, where you don't want to waste time cooking when you can simply keep your oil hot (spend a few minutes upfront, when you're not busy) and start cooking instantly.

For most home cooks however, this doesn't matter.

The second answer is it depends. Different oils have different smoke points. http://en.wikipedia.org/wiki/Smoke_point

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    Personally, I prefer to heat the oil along with the pan because the color of the oil gives clues as to whether or not the pan is at the right temperature to start cooking.
    – zacechola
    Dec 22, 2010 at 17:46
  • Disagree on leaving the oil sitting there. Would be difficult to maintain the exact right temperature. Also, it's a safety hazard - even just the burner being on, much less the hot oil.
    – zanlok
    Jan 27, 2011 at 4:26
  • There is a device tailored to keeping oil safely at a preset temperature. It is called a deep fryer :) But keeping oil idle at saute temperature will degrade it quickly...
    – rackandboneman
    May 14, 2018 at 8:30

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