All olive oils can be classified into one of two groups - Virgin and Non-Virgin oils.
If the oil is classed as Virgin, this means it is made naturally by pressing fresh olives and without the use of chemical processes or excessive heat to extract or refine the oil. This is olive oil in its purest and most natural form. However, not all olive oils are made this way.
If the oil is classified as non-Virgin, this usually means the oil has either been extracted or refined using chemical solvents or heat (or both). These processes remove flavour and beneficial antioxidants from the oil and what is left is incomparable to a Virgin oil.
Virgin olive oils are “cold-pressed” which means the oil is extracted using mechanical processes at a temperature not exceeding 25°C. This retains the oils chemical structure and beneficial antioxidants. This process only uses fresh olives hence the term “Virgin” - as this is the first time they have been pressed.
Non-Virgin olive oils are made either from spoilt virgin oils which require refinement before consumption (for example to reduce an excessively high acidity level) or they are made from the leftover paste from the already pressed olives. Chemical solvents and heat are required to extract the residue oil from the leftover paste and this process leaves an oil which is near colourless and tasteless.
Solvent extraction is also used to extract oil from seed-based oils such as sunflower, rape, soybean etc.
Virgin oils are not refined after pressing and the oil is sold in its natural state. The acidity of oil is a key quality indicator and the grading of Virgin oils has specific requirements regarding acidity levels. For example, Extra Virgin olive oil can have an acidity level no higher than 0.8%. A Virgin oil, on the other hand, can have an acidity level up to 2.0%.
All non-Virgin oils have been refined by chemical or physical processes to correct significant defects to make the oil fit for human consumption. Not only does this process remove undesirable substances and qualities from the oil, but it also removes beneficial qualities. What is left is a colourless, tasteless refined oil which does not have any of the natural antioxidants or anti-inflammatory properties of the natural oils.
FATS REMAIN, ANTIOXIDANTS DISAPPEAR
Virgin olive oil is 97% fat and the remaining 3% is a wide range of substances responsible for the aroma, taste, and its antioxidant effects. These are mainly polyphenols, vitamin E and beta carotenes. Most of these substances are destroyed during the refining process.
As a result, refined oils retain the same fat composition as virgin oils, including the beneficial monounsaturated fatty acids, but lose their highly valued antioxidant and aromatic properties.