The acidity level provides us with information on the quality of the raw material used to produce the oil and on the means of storage. Products with a low level of acidity were probably obtained from healthy olives, gathered from the tree and treated rapidly thereafter, while oils made from olives that have been attacked by parasites, harvested using methods that involves keeping them on nets or on the ground before they are processed – perhaps after a long time – have higher acidity levels, sometimes so high they are not fit for consumption. It is worth pointing out that the acidity of an oil cannot be perceived by tasting it.

The peroxide value, expressed as the amount of oxygen that has reacted with the oil, indicates the state of oxidation of the oil. An oxidized oil is very likely to have been conserved and processed inappropriately. In addition to air and light, the factors that boost the formation of peroxides are high temperatures and the traces of any metals present in the oil; it is important to keep these values under control, both while the olives are stored before being processed and during the conservation of the finished product. The factors described above also facilitate a number of chemical reactions that can damage the product even after purchase; this is why oil – like other food products – should always be stored away from light and heat.

Wax esters are compounds naturally present in the protective coating of the fruit and leaves of plants, and are a quality index. A low wax content is indicative of healthy fruit, picked from the tree when at the correct stage of ripeness.

This parameter determines the purity of extra-virgin olive oils. Specifically, a value higher than the legally established limit (0.2%) indicates the possible presence of seed oils.