Virgin olive oils are categorized and classified according to their content of free fatty acids, acidity. Essentially the acidity of the olive oil is what will determine its quality.
Acidity is one of the indicators of evaluation and classification of an olive oil. It is usually expressed as a percentage and represents the percentage of free fatty acids. It is one of the main criteria for the quality of olive oil, as the lower the acidity, the better the quality of the olive oil.
The acidity of olive oil is due to various factors, the main of which are the way the fruit is harvested and stored as well as its ripening stage.