Warming Up Olive Oyl

Awhile back some of we cooking instructors and nutrition nerds got in a snit about olive oil and whether it was “safe” to heat it.  I was prompted to seek a definitive answer when one of my students, who was vegan, was perplexed by what fat to use to make a cookie.  Butter was out and for whatever reason coconut oil wasn’t working for this student.  She was considering extra virgin olive oil (EVOO in Rachel Ray jargon).  I wrinkled my nose thinking about the taste of an olive oil cookie.  But this person had trepidation because “heated olive oil will oxidize and be toxic to my body”.

Really?  Could that be?  How did this student garner this particular fear?  And did it have any validity?  Shouldn’t Rome have fallen much sooner if this was the case?

I went for the big guns – Dr. Mark Kestin, PhD in nutrition and a mind like a biochem data base.
Here’s his answer:
“Firstly, as you probably already know, the smoke point of a cooking fat or oil is the temperature at which the chemical bonds between the fat molecules (trigyclerides) begin to break down and get turned into other compounds.  EVOO has a low smoke point as it has a little water and some other stuff in it.  All this means is that you should not deep fry with EVOO but you can sauté or bake with it – think of it a little like butter which also has a low smoke point.

Secondly, when you overheat an oil, and especially if you use it again and again for deep frying, the polyunsaturated fatty acids get oxidized and make a number of substances, some of which may be carcinogens, but definitely affect the flavor, texture, color etc.  As olive oil does not have many  polyunsaturated fats it is less likely to do this than say sunflower or canola oil.  But considering you shouldn’t be deep frying with it in the first place it is not really a practical problem.

Thirdly, EVOO has some unique compounds (the chemicals are called phenols) which are believed to have specific health effects separately from the monounsaturated fat.  There is less work done on how stable these compounds are.  I have seen two or three studies that found that shallow frying with EVOO led to about  30% loss of the compounds in total (80% was lost if the oil was used for frying 8 times).  To put this in perspective, this is less than the loss of vitamin E and if you store EVOO for 4-6 months in the dark you lose about 40% of these compounds (and you lose about 60% if stored in diffuse light).  However, some of these compounds are more fragile than others but we don’t know enough to say which is most important for health effects.

My take overall is that baking or sautéing with EVOO should be OK if you don’t reuse it.  It may be more important not to store too long and to keep it in the dark.”

So that’s my overall take too.  Thank you Dr. Kestin.  Slays me how we have to prove that the simple way we have made food taste fabulous for centuries is safe.   Of all the things out there that truly could be labeled “toxic”  I’m running around defending a beautiful bottle of organic EVOO.  Silly rabbit.

13 thoughts on “Warming Up Olive Oyl

    1. My understanding is that as long as the oil is not smoking, it is safe. I happily roast potatoes at 400 to 450 degrees that have olive oil on them. They taste fantastic.

  1. That’s always been my rule of thumb – don’t let the oil smoke. (And just because the oven is higher than the smoke point doesn’t mean the food is that hot.)

    I have a major quibble with the folks from America’s Test Kitchen/Cooks Illustrated who OFTEN instruct to heat oil in a pan “until it begins to smoke” then add the food. Nooooo!!!!! The oil should be hot before adding the food, but definitely not at the smoke point.

  2. Also, just don’t deep fry? It seems like there have been enough studies that showed that food that’s deep fried has all manner of icky-for-us changes, whether or not it’s fried in an oil that has a high smoke point. The thought of reusing oil kinda gives me the willies.

  3. Love it. How about a “tweet” or “facebook” button so we can share specific posts w/ others?

    We recommended your website in our last NutritionWorks newsletter. :)

  4. I make a whole wheat butter pie crust that always smokes… it fills my kitchen! The crust is tender and it’s a great recipe in terms of how the crust turns out in the end, but the whole time it’s baking I’ve got all the windows open, fans blowing out, and I’m opening the oven door every 10 minutes to let the smoke out.

    I thought maybe the temp was too high (375), so I tried baking at 350, then 325… still no luck. I thought it was just the butter that was dripping out so I put foil under the pies and replaced it several times… still no luck.

    Any ideas; and, aren’t these temperatures lower than the smoke point for butter? Does it have something to do with the combination of whole wheat and butter?

    Sorry if this is getting off point too much- but this post was relevant to me as I JUST baked blackberry pies yesterday!

  5. :) Thanks so much for the feedback… but this has happened in at least 3 different ovens, and nothing else smokes when I bake it in my oven. That’s what’s so weird about it- every time with this recipe and this recipe only.

    I discovered your site looking for an alternative recipe, actually, and am thoroughly enjoying it (the website- I haven’t tried the crust recipe yet)! Thanks again-

  6. Terri S.,
    Have you tried Ghee? It is butter without the low molecular weight milk ingredients that usually burn at lower temperatures. You should get the butter flavor without the smoke.

    I would love to see your recipe. I am still trying to find a good tasting pie crust.

  7. I know this is going way off topic, but someone recently told me the same thing about honey, and that you shouldn’t use honey in your tea or in baking. I thought of you, Cynthia, because I always know you do your research and I trust what you have to say. I know it’s so easy for people to pass along info they heard from someone else, not knowing if it’s true or not. I searched your site but didn’t see anything about this…any thoughts? (Or you can point me in the right direction about where to look). Thanks, Lisa

  8. Hi Lisa,
    Some people claim that there are some beneficial enzymes in raw honey. Not true if the honey is pasteurized. So if you heat raw honey to the point of a simmer or boil, you would likely lose those enzymes.

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