Professional tasters pour a small amount of extra virgin olive oil (HOEV) into a blue stemless tasting glass. The blue glass darkens the color of the oil so that the taster is not biased by the appearance of the oil. The glass is held in the hand and swirled to warm the oil, then the aroma is felt. A good oil will have a nice aroma of fresh fruit; a bad oil will smell fermented or rancid. The oil is then sipped and mixed by drawing air around the teeth and lips. This volatilizes the oil, which amplifies its flavor. Once the oil coats the inside of the mouth, the taster swallows and exhales through the nose. This provides what is called the retro-nasal effect, further enhancing the flavor characteristics. A good oil should taste like fresh olive with a bit of bitterness and spiciness. Bad oil can taste slightly flat, fermented, greasy, or even rancid.
To see the sensory vocabulary to learn more about the qualities and defects of olive oil.