This is one of the enduring myths that just won't go away. In fact it has become so engrained in the minds of many, that I have heard leading chefs repeating the fallacy that good extra virgin olive oil should only be used chilly and never to cook with.
So let's knock this on its head once and for all. Yes you can cook and really should cook with extra virgin olive oil. Here's why.
A quick chemistry lesson
OK this is the science piece -- you can bypass it if you'd like and head straight to the end, but to really bust this myth I want to convince one fully.
Oils are made up predominantly of fats called triglycerides. These are made up of three (therefore the'tri') fatty acids attached to a compound called glycerol.
Oils also contain a very small number of free fatty acids -- in other words fatty acids that are not attached to glycerol and are'floating' in their own. The degree of free fatty acids varies between oils and varies with the quality of the oil. This is important, as we will discover.
The fatty acids within the petroleum, either as part of a triglyceride or free, can be saturated, monounsaturated or polyunsaturated. These names come from the chemical structure of the fats and the amount of what are called 'double bonds'. Saturated fats have no double bonds, monounsaturated fats have one, and polyunsaturated fats, as the name implies, have many.
You don't have to understand what these are school chemistry may be a distant memory -- but suffice to say that they are important because a double bond is the part of the fat that is prone to damage.
Damage (technically called oxidative damage) to double bonds is what creates trans fats -- the most damaging to our health -- and what makes a fat turn rancid. A rancid fat won't taste great, but it also contains potentially harmful compounds.
This damage to oils can happen with exposure to light, to air and also to heat, especially very high heat and heat. This is why you are best to keep any petroleum at a dark, cool pantry and also to use it up before the best before date to ensure freshness. It is also the reason we will need to take care with our choice of oils when cooking.
The smoke point is a term used to describe the temperature at which you will notice a bluish smoke rising constantly from the oil. (Notice that extra virgin olive oil is a natural product and so contains a little water.
This means that if you heat it into the pan you will often see steam rising well before the oil reaches its smoke stage -- don't confuse this and believe you are damaging the oil.) Heating the oil above its smoke point increases the odds of oxidative damage and the creation of potentially harmful compounds.
Since polyunsaturated fats have a lot of double bonds these fats are the most fragile and prone to damage. In contrast, saturated fats without a double bonds are really stable, whereas monounsaturated fats with just double bond are also exceptionally resistant to oxidative damage.
Free fatty acids are also more prone to oxidative damage and so oils with higher amounts of free fatty acids are also more fragile, especially during cooking.
The smoke point is usually provided as the definitive guide as to whether a kind of petroleum can be used for cooking. But, it is not the only important factor and it varies, even amongst one type of oil. This is where much of the confusion has come from.
Extra Virgin Olive Oil
Looking just at olive oils you'll find different smoke tips given, based on the source of the information. That's because it depends on the quality of the petroleum, how fresh it is, how it has been kept, the levels of free fatty acids and the levels of protective antioxidants.
So here is the crux of the matter. Extra virgin olive oil has three important qualities that make it an excellent cooking oil: it contains predominantly stable monounsaturated fatty acids, it has a low level of free fatty acids and it has a high level of protective antioxidants.
If we look at the smoke points of extra virgin olive oils, these range from about 190-220°C. The highest quality oils, such as Cobram Estate extra virgin olive oils, come in at the higher end of the range.
How does this relate to cooking? Well sautéing on the cooker equates to a temperature of around 120°C, deep-frying is usually in the range 160-180°C and roasting in the oven 180°C. It is not often you'd cook at any temperature higher than this.
Importantly there is no further advantage to using an oil or fat with an even higher smoke point. In other words, if you are roasting your veggies in the oven at 180°C, your extra virgin olive oil is perfect as it has a smoke point above this. Choosing an oil with a smoke point higher than 220°C is not any safer.
Why We Should Cook with Extra Virgin Olive Oil
Several excellent studies have confirmed the stability of extra virgin olive oil during cooking. Importantly these studies have really pushed the boat out to test the point at which various oils will break down. They repeatedly heat the oils, heat them for long amounts of time and take them up to extremely substantial temperatures.
These conditions could almost never happen in home cooking so the fact that extra virgin olive oil stands up consistently well in these tests really does confirm the safety of using the oil at home. The same is true of oils high in polyunsaturated fats such as sunflower or generic 'vegetable' oil.
Plus we have research showing that if we cook veggies in extra virgin olive oil, the overall level of antioxidants and other beneficial compounds rises significantly. So we get a double whammy benefit of the fats present and a greater availability of protective compounds.
Extra virgin olive oil has an unequaled body of research supporting its function as a protective, beneficial food in a healthy diet. It is very versatile and can be used cold in dressings and for drizzling, as well as in almost all cooking applications. In this regard it is not just safe but also beneficial for our health, and of course delivering exceptional flavor!
So do as the Mediterranean countries have traditionally done for hundreds of years and enjoy cooking with your extra virgin olive oil.