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The characteristics of lampante olive oil are so poor that it is not suitable for human consumption. These oils have a high level of acidity, very unpleasant flavours and aromas, and, in some cases, an unusual colour.
To make lampante olive oil suitable for consumption, it must undergo a series of chemical and physical processes collectively known as the refining process, which remove its undesirable characteristics. The drawback is that many of these processes also remove the compounds responsible for the beneficial properties of olive oil.
Some of the refining processes described below are intended solely to improve the appearance of the oil and are not related to making it suitable for consumption.
1. Degumming. By adding water and phosphoric acid, compounds such as phospholipids and gums are removed. These substances may cause the formation of deposits in the bottle (see sediments in olive oil), which are considered unattractive to consumers. Unfortunately, some desirable compounds, including certain proteins, are also removed during this process.
2. Neutralisation. This stage removes the oil's acidity. Caustic soda is used to neutralise the free fatty acids, reducing the acidity to almost zero. However, the process also removes a significant proportion of the carotenoids, including compounds with provitamin A activity.
3. Bleaching. This process removes the substances responsible for the oil's colour, mainly carotenoids and chlorophyll. The oil is treated with activated bleaching earth at approximately 100 °C.
4. Deodorisation. Heat is used to remove the compounds responsible for unpleasant tastes and odours. As most of these compounds are volatile, they are eliminated by passing steam through the oil at temperatures of 200–250 °C. Free fatty acids are also removed during this stage. Unfortunately, most tocopherols, sterols and polyphenols, together with their valuable antioxidant properties, are also lost.
5. Winterisation. This process removes triglycerides with a high melting point, allowing the oil to remain liquid at lower temperatures. The oil is cooled, causing these triglycerides to solidify so that they can be separated. As with degumming, its main purpose is to improve the appearance of the final product (see olive oil sediments).
The final product obtained after refining lampante olive oil is refined olive oil. It can be said that, from the original composition of virgin olive oil, almost only the triglycerides remain, as most of the unsaponifiable fraction has been removed. The unpleasant colour, taste and aroma of lampante olive oil disappear, but so do many of the compounds responsible for the antioxidant and anti-inflammatory properties of virgin olive oils.
As a result, refined olive oil is a colourless, odourless and virtually tasteless vegetable oil. It differs from other vegetable oils mainly because of its high oleic acid content, which is the principal nutritional characteristic retained after refining. In this form, refined olive oil cannot be marketed directly, as it would not be accepted by consumers. Before being sold, it must be blended with virgin or extra virgin olive oil to provide colour, flavour and aroma.
More recently, there have been attempts to replace the chemical refining stages, particularly degumming and neutralisation, with more intensive physical treatments involving higher temperatures and longer processing times. Although this approach avoids the use of chemical substances, prolonged exposure to heat may alter the composition of fatty acids, particularly linoleic acid (omega-6) and linolenic acid (omega-3).