Olive oil is a kitchen staple, but the facts behind it are less well known. Here are ten that are true, useful, and a little surprising.
1. Olive trees can live for centuries
An olive tree that is looked after can keep producing fruit for hundreds of years. Some trees around the Mediterranean are thought to be well over a thousand years old. Their exact age is hard to prove, because old trunks often hollow out and lose the growth rings that would date them. Even when the trunk fails, the tree can send up new shoots from its base.
2. Olive oil is pressed from a fruit
An olive is a fruit, related in structure to a cherry or a plum: flesh around a hard stone. The oil comes mainly from that flesh. Virgin and extra virgin olive oils are obtained only by mechanical means, crushing the olives and separating the oil, without chemical solvents or refining. In that sense it has more in common with a fruit juice than with a refined oil.
3. There is one harvest a year
Olives are picked once a year. In the northern hemisphere that is roughly autumn into winter, from around October to January, depending on the region and the style of oil the producer wants. Earlier picking generally gives greener, more bitter and peppery oil. Later picking gives a softer, rounder one.
4. Extra virgin is a legal grade, not a marketing term
To be sold as extra virgin, an oil has to pass two kinds of test. The first is chemical: limits on things like free acidity, which must be no more than 0.8%, plus several other measures of freshness and purity. The second is sensory: a trained tasting panel must find no defects at all and some fruitiness. Fail either test and the oil cannot carry the name.
5. “Cold” on a label has a specific meaning
Under UK and EU rules, “first cold pressing” may only be used for virgin or extra virgin oil made below 27°C in a first mechanical pressing with a traditional hydraulic press. “Cold extraction” may only be used for oil made below 27°C by percolation or centrifuging. Most olive oil today is extracted by centrifuge, so “cold extraction” is the accurate term for most of it.
6. Light, heat and air are the enemies
Olive oil does not improve with age. Light, heat and oxygen all speed up the slow decline in flavour. That is why good oil comes in dark glass or tins, and why the best place to keep a bottle is a cool, dark cupboard away from the hob, with the cap on.
7. Colour is not a sign of quality
Olive oil can be deep green or pale gold, depending on the olive variety and how ripe the fruit was. Neither colour tells you whether the oil is good. Professional tasters use small, dark blue glasses so the colour cannot sway their judgement. Your nose and your tongue are better guides than your eyes.
8. Bitter and peppery are good things
In official tasting, there are three positive attributes: fruity, bitter and pungent. Pungent is the peppery catch at the back of your throat that sometimes makes people cough. Bitterness and pepperiness come from natural compounds in fresh olives, and they tend to soften as the oil ages.
9. You cannot eat an olive straight off the tree
A raw olive is intensely bitter, so bitter that it is not pleasant to eat. Table olives have to be cured first, using brine, water, dry salt or a lye solution, sometimes followed by a long fermentation. Curing breaks down or draws out the bitter compounds.
10. Olive trees take turns
Olive trees are known for alternate bearing. A heavy crop one year is often followed by a lighter one the next, as the tree recovers. Careful pruning can reduce the swing, but rarely removes it. It is one reason the amount of oil from the same grove can change a lot from year to year.
Putting it to use
Most of these facts point the same way. Buy extra virgin, look for a harvest date, choose dark glass or a tin, keep it somewhere cool, and use it while it is fresh.
Our extra virgin olive oil comes from Dukat, in Vlorë county, Albania. It is bottled in 0.5 L dark glass, with the harvest date and batch code on every bottle, so you know which harvest you are pouring. If you would like to taste it, you can find it here.