How do I know if an olive oil is good or not?
Taste it. Pour a little into a small shot glass or on a spoon and slurp it down. Close your eyes and really taste it. If you’re tasting an extra virgin olive oil, it should taste “green” and like olives. You might detect other notes like banana or grass. Other grades will not taste like much because they have been treated to remove unpleasant tastes. But you should not detect any bad tastes, such as cardboard or metallic. You might sometimes taste nice flavors in lower grades due to the small amount of extra virgin that is added. To learn more about tasting olive oil see An Introduction to Olive Oil Tasting.