Can you cook with extra virgin olive oil?
There is no doubt that extra virgin olive oil is good for us. But cooking with it is a very hot topic of debate, particularly on social media. Some praise its rich flavour and health benefits for cooking. Whereas, others bring up the smoke point, and that its usage should be reserved for salads. So let’s explore the research.
What is the difference between extra virgin olive oil and olive oil?
Before we jump into the science, we need to break down the different types of olive oil and what makes them unique.
There are several types of olive oil, but the key difference lies in how they are made. The following points summarises the different types of olive oil available for consumption:
- Extra virgin olive oil – Is olive oil in its purest form. Extra virgin olive oil is first cold pressed, meaning that the oil is extracted by crushing the olives. This method uses no heat or chemicals, so it retains more nutrients and flavour. It also contains polyphenols, which are natural compounds found in plant foods that have antioxidant properties. This is why high quality extra virgin olive oil has a premium price.
- Virgin olive oil – Is a lower grade and considered less healthy than extra virgin olive oil. After the first cold press, the olives are then cold pressed again to extract the virgin olive oil. So it contains a moderately high amount of antioxidants naturally.
- Olive oil or pure olive oil – Is made mostly from refined olive oil and roughly 5-15% extra virgin or virgin olive oil. So it is much lower in nutrients and antioxidants.
- Refined olive oil – Is made from lower quality virgin olive oil that is heavily processed. The refining process causes the olive oil to lose its antioxidants and nutrients. It also increases the amount of trans fats.
- Olive oil pomace – Is made from the leftover olive pulp. Using solvent chemicals, the remaining liquid is extracted from the crushed olives. It is then combined with virgin olive oil. Pomace is also heavily refined, so nutritionally it is about the same as refined olive oil.
The science behind oils
All oils are made up of long chains of fatty acids. These fatty acids are broken down into 3 different categories: saturated, monounsaturated and polyunsaturated.
The difference between these types of fatty acids comes down to the number of double bonds (=) they have in the chain (picture for reference).
- Saturated fats – Contain no double bonds. This makes them solid at room temperature.
- Monounsaturated fats – Only one double bond.
- Polyunsaturated fats – Have two or more double bonds.
The nutrition of extra virgin olive oil
Being a fat, oils have 37 kilojoules / 9 calories per gram. In general, cooking oils contain all 3 different types of fats. However, the ratios of these fats differs depending on the type of oil.
For example, coconut and palm oil is primarily made of saturated fat. As saturated fat contains no double bonds, they are solid at room temperature.
Safflower, flaxseed, walnut, sunflower, corn and soybean oil are mostly made of polyunsaturated fats. Finally, olive, canola and peanut oil is largely made of monounsaturated fats. This will be important further down. Due to containing double bonds, these fats are liquid at room temperature.
Olive oil has more monounsaturated fats than canola or peanut oil. Extra virgin olive oil is made up of ~70% oleic acid, a type of monounsaturated fatty acid (a single double bond). Additionally, it also contains smaller amount of polyunsaturated fats (~15%), which is a mix of omega 6 (linoleic acid) and omega 3. But also a small amount of saturated fat (~15%).
Smoke point
All cooking oils have a smoke point, regardless of how they are processed. This also includes organic oils. The smoke point of an oil refers to the temperature at which it starts to visibly produce smoke. Many people believe that heating cooking oils beyond their smoke point is harmful. As it can create trans fats and other harmful compounds. For reference, here’s a list of the average temperature for different home cooking methods:
- Boiling – 100ºC / 210°F
- Steaming – 100ºC / 210°F
- Roasting – 180ºC / 355°F
- Microwaving – 100ºC / 210°F
- Deep frying – 170-180ºC / 340-533°F
- Pan frying – 200-220ºC / 390-430°F.
The science behind smoke point
Heating an oil beyond the smoke causes the oils to break down and lose its nutrients. This is a known as oxidation. The high heat disrupts the bonds in the long chains, causing the fat to break down. Double bonds are more easily damaged by heat. So polyunsaturated fats are more likely to oxidise from heat because they have more double bonds. While saturated and monounsaturated fats are better at resisting heat.
When an oil oxidises, it can release harmful polar compounds, such as free radicals. Ideally, we want to try and reduce the amount of free radicals in our bodies. These free radicals can cause damage to our cells, known as oxidative stress. Chronic and prolonged exposure to oxidative stress has been linked to certain diseases.
The smoke point of oils
However, the actual smoke point can vary among the different types of oils. For example, sunflower oil, despite being mostly made from polyunsaturated fats, has a very high smoke point at 267°C / 529°F. Whereas, extra virgin olive oil’s smoke point is more towards the middle, at 206°C / 403°F. Take note, that a lot of refined oils like grapeseed, sunflower, canola etc, have a much higher smoke point than extra virgin olive oil.
What the research says
In 2018, a study looked at the changes in the most common cooking oils when exposed to high temperatures. They recorded results on trans fat levels, the amount of polar compounds produced from each oil and oxidative stability.
Trans fats
Grapeseed oil developed the most trans fats after 6 hours of heating. While canola oil had the most trans fats after reaching a temperature of 240°C / 464°F. In contrast, all the olive oils, avocado and coconut oil, produced the least amount of trans fats. The key difference is that these oils are unrefined and produced naturally. Whereas, grapeseed and canola oil are heavily refined, so they contain more trans fats before heating.
Production of polar compounds
The oils were heated to 240°C / 464°F over a 20 minute period. During this time, the extra virgin olive oil produced the least amount of polar compounds. Whereas, canola oil produced the most at a whopping 27.5%.
For the second test, all the oils were heated to 180°C / 355°F for 6 hours in a deep fryer. Both extra virgin olive oil and coconut oil produced the least amount of polar compounds by the 6 hour mark. Whereas sunflower and grapeseed oil, produced the highest amounts of polar compounds.
Oxidative stability
Heating an oil increases its exposure to oxygen, which causes it to oxidise. On the other hand, oxidative stability is an oil’s ability to resist oxidation when exposed to oxygen. Thus, the more resistant an oil is to oxidation, the better it is for cooking.
Looking at both of the graphs below, you can see that coconut oil starts off with the highest oxidative stability. But when being heated to ~215°C / 419°F, extra virgin olive oil became the most stable. Remember, both peanut and extra virgin olive oil are monounsaturated fats. So even though they each have a single double bond, they were both more stable than coconut oil.
Coconut oil continues to be the most stable between the 3 – 6 hour mark while being heated at 180°C / 355°F. This is because coconut oil is ~90% saturated fat, meaning it has no double bonds. That being said, extra virgin olive oil also started off relatively high. During the 30 mins – 2 hour mark, it became more stable than coconut oil at 180°C / 355°F. Interestingly, all of the heavily refined seed oils are at the bottom of both charts. This is because, despite their high smoke points, they are mostly polyunsaturated fats.
So over all, this also tells us that extra virgin olive oil is a great choice for cooking. Both at really high temperatures and for 2 hours or less.
Polyphenols
The amount of antioxidants in the oil also plays a role during heating. Polyphenols are a group of natural compounds found in plants that have antioxidant properties. What sets extra virgin olive oil apart from other cooking oils is its very high polyphenol content.
Several studies claim that the antioxidants in extra virgin olive oil protect it from oxidation when heated. One study found that while heat degraded some antioxidants, most were retained. Another study compared the oxidation levels of different oils after 27 hours of heating. The authors found that extra virgin olive oil resisted oxidation better than regular olive oil. They attributed this resistance due to it’s high antioxidant content.
Lastly, a study highlighted that the polyphenols in extra virgin olive oil can prevent oxidation. These polyphenols stop other compounds forming, which increases oxidative stability during heating. Although the heating process does reduce the amount of polyphenols. Extra virgin olive oil retains many polyphenols and some antioxidant activity even after heating. However, all studies agree that the polyphenols degrade more at higher temperatures (220-240°C / 428-465°F).
These claims are reinforced by the PREDIMED study. In this study, a group of participants were required to follow a Mediterranean diet with extra virgin olive oil (including for cooking). Participants assigned to this group had a reduction in cardiovascular events.
Should I only use extra virgin olive oil?
Despite what the research is saying, it doesn’t mean you have to stick to only extra virgin olive oil. There are no right or wrong answers here, so you can use other oils.
You’ve probably noticed that I use extra virgin olive a lot in my cooking! For example, I use it for:
- Baking – like in my Nutty Apple Cinnamon Bread or Pistachio & Matcha Cake,
- Roasting – such as in my Curry Cauliflower Potato Salad,
- Pan frying – in my Pork Steaks with Balsamic Glaze.
However, I’m a big fan of the 80/20 rule. So using extra virgin olive oil 80% of the time, and the remaining 20% for other oils. When it comes to cooking, I prefer to use extra virgin olive oil. While other natural oils like avocado oil, I would reserve for uncooked foods, like salads.
Summary
The research shows that smoke point is not a reliable indicator an oil’s stability during cooking.
Extra virgin olive oil is a better option for cooking compared to most oils. This is due to its ability to resist oxidation and retain antioxidants at high heat. Considering the average home cooking temperature is generally around 160-180ºC (320-355ºF). Plus the fact that there is no shortage of studies that show the benefits of extra virgin olive oil for health.
Anyhow, I’d love to hear if you found this article interesting, or if it changed how to looked at extra virgin olive oil? And feel free to let me know in the comments if there is anything else you would like to know or any other topics you’d like me to cover.
