Look for ‘extra virgin.’ Oils that earn the highest grade conferred by the International Olive Council must pass a taste test and have very low acidity. Beware the terms “refined” and “pure.” The first designates oil that’s been processed with solvents to mask odd odors and flavors. The second, oddly, describes a blend of virgin and refined.
Check the harvest date. Olive oil is good for about two years, and fresh olive oil tastes better than older oil. Also, note where the oil is from. If it was “produced” in Italy but the olives were grown elsewhere, the travel time likely caused some degradation.
Think domestic. California oils “consistently score higher in quality than -imports”—probably because they’re fresher.
Sample it at home. Taste the oil when you get it home. If it tastes or smells of wax, salami, or peanuts, it’s rancid, so return it.