Acidity indicates a hydrolytic phenomenon of oxidation and its state of progress.
Acidity is the main quality parameter, is a parameter that indicates olive oil freshness: a high acidity value shows the oil is becoming rancid, thus the oil quality is decreasing. Acidity can not be discovered merely through laboratory tasting.
Olive oil is called extra virgin when its acidity is below 0.8%. A low acidity value indicates an extraction process made soon after the olive harvesting and with natural, non-chemical methods, and also depends on the way the operators adhered to the process during the treatment and storage phases.