The quality criteria for olive oils are described in detail in the Codex Alimentarius (FAO and WHO standards) and in a regulation of the European Commission. Among these criteria, the most important is the content of free oleic acid. It is defined as the percentage, measured by weight, of the free oleic acid that the oil contains. The acidity of extra virgin olive oil must be less than 1 %.
Fatty acids, which comprise approximately 99 % of olive oil, degrade over time, from the moment the olives are harvested. When the oil is extracted the degradation is relatively slow, provided that the oil is not in contact with air and light, which promote its oxidation.
This acidity is not perceived as an acid taste. However, the products resulting from the oxidation alter the original taste of oil giving it, for example, a musty taste.
Low acidity is not the only criterion of quality, but it is an important one and it is often the only one indicated on the label. Being aware of the acidity level when choosing a fine oil is therefore an important factor to take into account.
