Why are some olives black?

Why olives change colour

An olive changes colour on the tree, just like a banana goes from green to yellow or a cherry from green to red. It starts green, then turns a bit yellow, then pink, purple, brown and finally black.

The dark colour comes from natural colours inside the fruit, the same kind that make grapes and blueberries dark. A green olive is simply an olive that was picked before it had time to change.

Natural black olives

Natural black olives stay on the tree until they are ripe and dark. Then they soak in salty water, called brine, for several months. Slowly the brine takes away the bitter taste.

They taste fruity and strong, they are a bit firm when you bite them, and their colour is never exactly the same. Some are brown, some purple, some almost black, just like real fruit.

They cost more to make. The farmer has to wait for them to ripen, ripe olives bruise easily when they are picked, and the soaking takes months.

Oxidised black olives

Oxidised black olives start as green olives. They go into a special water bath, and air is bubbled through it. The air turns the olives dark, a bit like a cut apple turns brown when you leave it out. Then a little iron, called ferrous gluconate or E579, keeps the black colour from fading.

This only takes about a week. Afterwards the olives are sealed in jars or tins and heated, so they stay safe.

They come out shiny black all over, soft and mild. That is why you often see them on pizza. Some people taste a tiny bit of metal from the iron.

How to tell them apart

Look at the colour. Oxidised olives are the same shiny black everywhere. Natural ones have shades of brown and purple.

Look at the stone inside. It is pale in oxidised olives and dark in natural ones.

Read the label. If it says ferrous gluconate or E579, the olives are oxidised.

Which one is better?

Neither. They are just different. Natural black olives are great when you want to taste the olive itself, on a plate of snacks or in a salad. Oxidised black olives are great on pizza and in sandwiches, where a soft bite and a mild taste work best. Both are safe and good to eat.