When olive is picked up from the tree it is far bitter to eat, but you know that this bitterness is so amazing for your health ! This bitterness is due to antioxidants- Tocopherol and Polyphenols respectively. Antioxidants contributes many health benefits.
The extra virgin olive oil is fresh juice simply made by crushing olives,that's why high quality olive oil tastes bitter with pungency.The degree of bitterness depends upon how ripe the olive is, bitter olive oil is positive thing.However after a couple of month the olive oil become mellow,softer and milder.But the olive oil that are too older, tastes rancid and having greasy texture.
source- olive oil times.