The colour of olive oil tells you nothing

There is a widespread belief that green olive oil is better than golden olive oil. It is not true, and the way the industry officially judges oil demonstrates this rather plainly.

The blue glass

In official assessment, olive oil samples are served in dark coloured glasses — usually deep blue. The purpose is single: so the taster cannot see the colour at all.

This is not because colour does not matter to consumers. It is because colour was identified as a source of bias that influences judgement without supplying any useful information.

What actually determines the colour

• The olive variety — some naturally produce greener oil
• How ripe the fruit was when picked — green fruit gives greener oil
• The quantity of chlorophyll and carotenoids in the fruit
• Whether the oil was filtered after separation
• How long the oil has been in the bottle

Note that none of those relates directly to quality. Excellent green oil exists, and poor green oil exists. The same is true of golden oil.

Why the myth persists

There is a grain of truth behind it, which makes it harder to dislodge. Early harvest oil tends to be greener, and it also tends to be higher in polyphenols. So green and quality sometimes appear together.

But "sometimes appear together" is not the same as "causes". Colour can be altered by filtering, by variety, or — and this happens — by adding colouring. Colour is the easiest thing on a bottle of oil to fake.

What to look at instead

1. 1.Smell. Sniff it — it should smell of fruit, grass or tomato leaf, not of nothing
2. 2.Bitterness at the back of the tongue
3. 3.Pungency in the throat a few seconds after swallowing
4. 4.The laboratory figures: free acidity, peroxide, K270
5. 5.A harvest date on the label

Dark glass bottles exist for an entirely different reason from the oil's colour: they block light, which damages oil. That is a good reason to choose a dark bottle, and it has nothing to do with the colour of what is inside.