Eight things hidden in the olive and its oil

That peppery catch at the back of your throat from a fresh green olive oil is a real drug effect. The culprit is a natural compound called oleocanthal, and in 2005 researchers found it acts on the very same inflammation enzymes as ibuprofen. The sharper the sting, the more of it is present — the throat-tickle is essentially the oil announcing its anti-inflammatory dose.

An olive is not a vegetable but a drupe — a stone fruit built exactly like a peach, cherry, plum or mango, with a thin skin, soft flesh and a single hard pit guarding the seed. The savoury olive on a plate and the sweet cherry in a bowl are close botanical kin; the difference you taste is mostly bitterness and oil, not family.

Those uniformly jet-black canned olives were almost never ripened on the tree. They start as unripe green olives, are cured in lye, then have air bubbled through them again and again so oxygen darkens the flesh. A pinch of an iron salt, ferrous gluconate, locks in the deep even black. Truly tree-ripened olives are blotchy purple-brown, never that perfect uniform colour.

Pick an olive and bite it and you will spit it straight out — raw olives are brutally bitter, loaded with a compound called oleuropein. Every olive you have ever eaten was first tamed: soaked for weeks in water, brine or lye, or packed in salt, to leach that bitterness away. The fruit evolved the bitter chemical to stop animals eating it before the seed inside was ready.

When olives are pressed for oil, a wet brown paste of skins, pulp and crushed pits is left behind. That waste is not thrown away: it is dried and washed with a solvent to wring out a last couple of percent of low-grade oil, and the exhausted dry cake is then burned as fuel to help power the mill itself. Almost nothing of the fruit goes to waste.

Olive trees keep their own rhythm. A heavy 'on' year, when the branches bow under fruit, is usually followed by an 'off' year with almost nothing — a swing called alternate bearing that growers fight constantly. Patience is needed from the start, too: a young tree planted from scratch often takes three to five years before it bears its first real crop, and longer to hit full stride.

Olive trees may be the longest-living fruit trees on Earth. One gnarled giant on Crete has been dated by its rings to at least 2,000 years old, with some estimates reaching far higher, and it still sets fruit every season. Even when the trunk rots hollow or burns, an olive resprouts from its root crown, which is why ancient groves seem almost impossible to kill.