Professional olive oil tasters use blue glasses so the colour cannot bias them, but everything else about their method works at your kitchen table. Here is the four step version we use for every oil in our rankings.
1. Warm it. Pour a tablespoon into a small glass, cup it in your palm and cover the top with your other hand for a minute. Warmth releases the aroma.
2. Smell it. Good oil smells of something alive: cut grass, tomato leaf, green apple, artichoke. Bad oil smells of nothing, or worse, of crayons and old nuts. That waxy smell is rancidity, and once you learn it you will notice it everywhere.
3. Slurp it. Sip the oil and draw air through your teeth over it. Undignified, but it sprays the oil across your palate. Notice the fruitiness up front and any bitterness in the middle. Bitterness is a good sign, not a flaw.
4. Wait for the pepper. A fresh, high polyphenol oil finishes with a peppery catch at the back of your throat. Tasters grade oils as one cough, two cough or three cough. If you feel nothing at all, the oil is likely old or heavily refined.
Run this test on the bottle you own tonight. If it fails, our ranking of the 33 best olive oils in the world is a good place to find its replacement.