A number of different classifications exist, most importantly, 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. On the other hand, refined oils have been subject to chemical processing, excessive heat or any number of different processes before being sold.
Extra virgin olive oil
Extra virgin olive oil is simply the mechanically extracted juice of the olive. They should display true olive 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 they have been made from quality olives, processed soon after picking, and made using minimum heat.
Extra virgin oils are the healthiest choice. All the natural antioxidants, such as polyphenols and vitamin E, are retained because of the natural extraction process and the oil’s close connection with the olive flesh.
Virgin Olive Oil
To be classified as virgin olive oil, it must be extracted from quality olive fruit by the mechanical processes of milling, pressing and centrifuging, and must also meet some basic tests to ensure there has been no alteration in the nature of the oil. It is important to note that virgin olive oils differ from extra virgin olive oils as they are more acidic and may display some sensory defects.
Refined Olive Oil
Refined oils are olive oils of inferior quality that have been through chemical processes such as gum extraction (where mineral acids are applied to remove acidity from the oil), neutralisation (adding strong alkali to remove excess free fatty acids), decolourisation (heating the oil and using clay or activated carbon to lighten the oil colour) and treating with superheated steam under a vacuum. These olive oils can be classified under many different names, the most common of which are ‘extra light’, ‘pure olive oil’ or simply ‘olive oil’.
Extra light oils are chemically refined oils. As they are refined, they are much “lighter” in aroma, colour and flavour (not kilojoules) than extra virgin olive oils. The fact is, all olive oils have a very similar kilojoule content. In Australia these ‘extra light’ olive oils are generally labeled as ‘olive oil’
Pure Olive Oil
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. As with ‘extra light’ a so-called pure olive oil will often be labeled ‘olive oil’.
The table below summaries some of the differences between the different types of oil.