A history of olive oil: six thousand years

The olive has been cultivated for roughly six thousand years, making it one of the oldest crops still widely grown today. It began in the eastern Levant and spread across the Mediterranean basin.

Why this tree and not another

The olive has three qualities that made it unusually valuable in the ancient world, and all three are practical.

1. 1.It withstands drought. It grows on rocky ground and dry slopes where other crops fail
2. 2.It lives a very long time. An olive tree can bear fruit for centuries, and some in the Mediterranean are estimated at over a thousand years old
3. 3.Its oil keeps. Unlike most food in a world without refrigeration, olive oil stays usable for months

It was not a cooking oil at first

This is the part that most often surprises people. In the ancient world, olive oil was used widely for things other than cooking.

• Lamp fuel — the most widespread use for thousands of years
• As a trade good, and sometimes as a stored form of wealth
• In religious ceremony across several traditions
• As a base for perfume
• For cleaning the body, before soap as we know it existed

Cooking was part of the picture, but it was not the whole of it. Olive oil was an industrial commodity of the ancient world.

Tunisia and North Africa

Olive growing in what is now Tunisia goes back thousands of years, and the region has been a major producer for much of that time. The conditions suit it: long dry summers, mild winters, and well-draining soil.

For much of modern history, a large share of Tunisia's output was exported in bulk to Europe, where it was bottled under other names. The more recent change is that more Tunisian oil is now bottled at source and sold under its own name.

What changed in the last hundred years

Two things. The first is that centrifugation replaced pressing as the main separation method, which sped up processing and reduced the time the oil spends exposed to air.

The second is standards. The International Olive Council defined the grades — extra virgin, virgin and the rest — with measurable limits for acidity, peroxides and ultraviolet absorbance. Before that, "extra virgin" had no checkable meaning.