The International Olive Oil Council has classified virgin olive oil by its acidity in the general categories set out below. To be classified as virgin olive oil, it must also be extracted from sound olive fruit by mechanical processes of milling, pressing and centrifuging and must meet some basic tests to ascertain that there has been no alteration in the nature of the oil.
A number of different classifications exist, but before one can understand them, we have to understand the differences between virgin oils and refined oils. Internationally, the word “virgin” when applied to olive oil means that the oil has been extracted mechanically using either a press or (more commonly) a centrifuge, without using excessive heat, and without the use of any chemical agents or means.
Extra Virgin Olive Oil
As they are of the virgin class, Extra Virgin oils must simply be the mechanically extracted juice of the olive. Extra Virgin oils should display true olive character with respect to aroma and taste and be free of any non-olive flavours. Chemically they have a free fatty acidity of less than 0.8%, which indicates that they have been made from sound olives, processed expeditiously, and made using minimum heat. As such they are premium grade oils.
Extra Virgin oils are the healthiest choice as the non-chemical extraction process employed in their production, retains the natural antioxidants called polyphenols and vitamin E. These substances have been implicated in reducing coronary disease. All olive oils contain high levels of monounsaturated fats, which as well as being ‘healthy’ fats, are also resistant to oxidation, so they last longer in storage, and can be reheated more often than many other cooking oils.
Refined Olive Oil
Refined oils as the name suggests are olive oils of inferior quality that have been subjected to chemical processes such as gum extraction (the application of mineral acids to aid in the removal of acidity from the oil), neutralisation (the addition of a strong alkali to remove excess free fatty acids), decolourisation (heating the oil and using clay or activated carbon to lighten the oil colour), treating with superheated steam under a vacuum).
Extra Light oils are chemically refined oils. As they are refined, they are much “lighter” in aroma and flavour, not calories, than extra virgin oils. In fact all olive oils whatever they are called have a very similar kilojoule content.
Pure Olive Oil
These are the same thing. The word pure is simply a marketing term. Pure olive oil is a blend of refined oil and some virgin olive oil, the latter being used to add some character to the almost flavourless refined oil.
The table below summaries some of the differences between the different types of oil.