One of the questions we are asked most often is what happens when olive oil is heated and/or used for frying?
You've probably heard that olive oil is great for drizzling and dressing, but bad for high-heat cooking like sautéing, frying and roasting. Maybe you've also heard that olive oil develops dangerous toxic compounds when you use it with high heat Well, guess what: Olive oil is perfectly safe to cook with!!
Cooking food is a little like carrying out a “magical” laboratory experiment. Behind the everyday practice of preparing a sauce, a pasta dish or a side of vegetables is an entire world of techniques, materials and methods that can play a far more important role than we can possibly imagine in making sure that food has a key say in shaping our overall health.
The choices we make in terms of cooking methods can have a positive or negative influence on the nutritional value and quality of the foods we cook. For every cooking technique from searing and sauteing to roasting and even deep-frying, the application of heat is needed and every one of these techniques has its own preferable working temperature.
The important thing about cooking with any oil is not to heat the oil over its smoke point. The smoke point refers to the temperature at which a cooking fat or oil begins to break down. The substance smokes or burns, and gives food an unpleasant taste. When this happens, the fat molecules are getting cleaved into glycerol and individual fatty acids, while also turning into various harmful and potentially toxic compounds. The other trace nutrients in the oil, like the vitamins and antioxidants, can also start to burn and give off smoke, sometimes at lower temperatures than the oil itself.
Usually, a portion of the fatty acids in an oil are free and not attached to glycerol. These are called free fatty acids. The more free fatty acids there are in an oil, the lower its smoke point.
Because refined oils are lower in trace nutrients (a bad thing) and lower in free fatty acids, they usually have a higher smoke point.
It is difficult to determine an oil's exact smoke point, because it doesn't happen all at once. There is a range in which a higher temperature forms progressively more smoke. Many of the numbers for smoke points you will find on the internet are just estimates. The numbers vary between different batches.
But what is the smoke point of olive oil?
Fatty acids in oils can be either saturated, monounsaturated or polyunsaturated. Saturated fatty acids have no double bonds, monounsaturated have one (mono = one) and polyunsaturated fatty acids have many double bonds (poly = many). Here's the important part... the double bonds are unstable when heated and they tend to react with oxygen.
Therefore, the more double bonds a fatty acid molecule has, the more unstable it will be when used for cooking. This is the reason saturated fats (zero double bonds) like coconut oil are very resistant to heat.
Although most vegetable oils contain polyunsaturated fatty acids with many double bonds, olive oil contains mostly monounsaturated fatty acids with one double bond.
The heat resistant monounsaturated and saturated fats in Extra virgin olive oil make up 87% and damage-prone polyunsaturated fats make up only about 11% of Extra virgin olive oil so it's actually pretty resistant to heating. The lower the free fatty acid content, the more stable the fat, and the higher the smoke point. Besides that Extra virgin olive oil also contains Vitamin E and many powerful antioxidants. These substances protect the oil from damage during high heat cooking.
Numerous studies have exposed olive oil to high heat for long periods of time and measured how it affects the quality and nutritional properties of the oil. Many of these studies used a high temperature for a very long time. But even under these extreme conditions, olive oil did pretty well. One study deep fried several different types of olive oil for 24 hours and noted that it was highly resistant to oxidation. Extra virgin olive oil, which is higher in antioxidants, did the best (1). Other studies agree with this - olive oil does not oxidize much when used for cooking, while vegetable oils like sunflower oil do oxidize and form harmful compounds (2).
Many sources put the smoke point of Extra virgin olive oil somewhere around 190-215°C. Refined olive oil is often placed around 240°C. This makes it a safe choice for most cooking methods, including most pan frying.
So normal cooking use is unlikely to oxidize or significantly damage the oil. However, it may degrade some of the antioxidants and Vitamin E, which are sensitive to heat.
In one study, heating olive oil at 180°C for 36 hours did lead to a decrease in antioxidants and Vitamin E, but most of the trace compounds were intact (3). One of the main active compounds in extra virgin olive oil is called oleocanthal. This substance is responsible for olive oil's anti-inflammatory effects and the burning sensation in the throat that quality olive oil brings (4). Heating olive oil at 240°C for 90 minutes reduced the amount of oleocanthal by 19% according to a chemical test, and 31% according to a taste test (5).
The trace compounds in olive oil are also responsible for some of its flavor. Therefore, overheating olive oil can remove some of the taste.
Keep in mind that the studies showing that heat degrades olive oil's antioxidants and vitamins are using rather extreme conditions.
Quality extra virgin olive oil is a SUPER HEALTHY FAT that retains its beneficial qualities during cooking. The main reason you may not want to use it, is that heating it too much can have adverse effects on the flavor.
The belief that olive oil oxidizes and goes rancid during cooking is a harmful myth that scares people from using this incredibly healthy fat – DON'T BE ONE OF THEM.