I’m quoting some simple and basic tips found inside the “Olio Officina Magazine”, one of the most important online publications dedicated to the world of olive oil and olives, edited and directed by Prof. Luigi Caricato
How to proceed. Once opened the bottle, pour a little bit of olive oil in a small plastic coffee glass: 15 ml of olive oil is enough, a bit more than a table spoon.
Cup the glass in one hand, to warm the oil up to about body temperature (about 28° C) but also to release and bring out all its volatile aromatic compounds.
The first tasting stage. Swirl the oil inside the glass, then inhale it deeply and slowly so as not to fatigue the sense of smell. You will smell immediately its distinguishing characteristics, its pleasant or unpleasant sensations. Quality oil has always clean and fresh aromas reminding of the green olive fruit: they should be perceived in a light, medium or intense way. But you may also notice other aromas: artichoke, tomato, green field grass, almond, apple … and many others.
Next you sip a small amount of oil (about 3 ml) into your mouth while “sipping” some air as well. It has to be done in a slow and gentle way at first, after you should actually slurp it, spraying the oil into the oral cavity, bringing it into direct contact with the taste buds and then, retro nasally, towards the olfactory bulb.
Leave to rest the oral cavity for a few seconds, slowly moving your tongue against the palate.
Sip the oil again, lips half-open, while keeping on moving your tongue against the palate.
If you are not sure of the taste and aromas, repeat the operation several times, keeping the oil in your mouth for at least twenty seconds, to be sure of the perceived tasting sensations. Keep on moving your tongue against the palate, carefully assessing the retro-olfactory sensations.
Spit the oil, you don’t have to swallow it. If you are about to taste different oils, it would be better to clean your mouth by chewing a slice of apple or drinking some water.
Olive oil to be considered good should have clear notes with fresh and clean aromas; it should be balanced and nice on the palate, pleasantly tangy. What the oil must not have, are some unpleasant tasting sensations like “warming up” (a characteristic of the olive oil obtained from piled olives having undergone fermentation), have a “Winey” (a scent reminiscent of wine or vinegar, due to olive fermentation), “rancid” (a scent of the oil that has undergone oxidation), or “cooked” flavour (due to the excessive and prolonged heating during the mill process).