Oils are made of fat molecules (triglycerides), which consist of a glycerol molecule linked to three fatty acids.  Fatty acids may be either saturated, monounsaturated or polyunsaturated - which are terms used to describe the number of ‘double bonds’ present in the chemical structure.  Saturated fats have no double bonds, monounsaturated have one, and as implied by the name, polyunsaturated fats contain many.

What’s important to know, is that double bonds become unstable when exposed to heat, oxygen and light – which is why you should always store your oil away in a cool, dark place.

Saturated fats contain no double bonds, which makes them extremely resistant to damage.  Monounsaturated fats are also highly resistant as they contain only one double bond, whereas polyunsaturated fats are the most fragile, containing numerous double bonds.

Also found in oils, are free fatty acids - those that aren’t buddied-up with glycerol.  The amount of free fatty acids in oil varies between oil type and quality.  Olive oil is low in free fatty acids, which is good news, as they tend to me more prone to oxidative damage.

The third aspect which makes olive oil a superior cooking oil, is its low smoke point.

The smoke point is defined as the temperature at which you see bluish smoke rising from the oil. It’s at this point that the oil is more likely to break down and form harmful compounds.