Its all about Acidity and Taste
Olive oil has two different classifications Extra Virgin and Virgin, the difference between the two is the amount of free fatty acid that the oil contains. To qualify as Extra Virgin, the oil must have excellent flavor and odor and free fatty acid of not more than 0.8g per 100 grams (0.8%). Virgin oil has reasonably good flavor and odor and free fatty acid content of not more than 2 g per 100 g (2%).
Since extra virgin olive oil is simply pressed fruit juice without additives, the factors influencing its quality and taste include the varieties of olives used, the terroir and the countless decisions, production practices and the dedication of the producer.
Excellent Extra Virgin Olive oil usually has the following attributes:
Fruity: Having pleasant spicy fruit flavors characteristic of fresh ripe or green olives. Ripe fruit yields oils that are milder, aromatic, buttery, and floral. Green fruit yields oils that are grassy, herbaceous, bitter, and pungent. Fruitiness also varies by the variety of olive.
Bitter: Creating a mostly pleasant acrid flavor sensation on the tongue.
Pungent: Creating a peppery sensation in the mouth and throat.