Extra virgin olive oil's reputation as a cornerstone of the Mediterranean diet rests largely on its polyphenols — natural antioxidant compounds that also happen to taste bitter and peppery. The flavours that beginners find challenging are, quite literally, the healthy part.
The throat-catching pungency of a fresh, robust oil comes substantially from oleocanthal, a compound shown to have anti-inflammatory activity compared (at the molecular level) to ibuprofen. The bitterness comes from related phenolics like oleuropein. These exist only in extra virgin oil — refining destroys them, which is why refined 'pure' and 'light' oils are smooth, bland and far less beneficial.
European regulators allow a specific, evidence-based health claim: olive oil polyphenols 'contribute to the protection of blood lipids from oxidative stress', for oils containing at least 5 mg of hydroxytyrosol and its derivatives per 20 g. In practice that means a fresh, genuine extra virgin — and the higher the polyphenol count, the stronger the claim and, usually, the more bitter and pungent the oil.
Polyphenol content varies hugely by variety, ripeness and freshness. Early-harvested, robust varieties — Coratina, Picual, Koroneiki, Moraiolo — can carry several times the polyphenols of a mild, ripe Arbequina. If you're choosing oil partly for health, lean bitter and peppery, buy it fresh, and use it raw or in low-heat cooking to preserve the compounds.
Polyphenols decline as oil ages and oxidises. A two-year-old oil, or one stored in heat and light, has lost much of both its kick and its benefit. The freshness obsession isn't just about flavour: with olive oil, fresh is healthy.