This is one of the best, short descriptions I have found. It’s from my very favourite Olive Company in the UK. Check them out!

Olive Et Al

There are few things more satisfying than a dish of plump glossy olives to enjoy with a glass of wine.

Olives, broadly speaking, are either green or black (or somewhere between the two). But what’s the difference?

When the fruit begins to form on the tree it contains no oil just a mixture of acid and sugar. Gradually, as the fruit ripens, the acid and sugar turn into oil whilst at the same time changing colour from palest green, through rose and violet to deepest aubergine and finally black. Whilst olives can be picked at any stage, the degree of ripeness determines the taste and green olives are totally inedible without being cured.

In their untreated state, green olives are very bitter and it is surprising that people ever discovered they were edible. Commercially produced olives are usually soaked in a soda solution to remove the bitter taste, they are then washed in clean water and finally packed in brine. This is the stage at which they are offered for sale. In the UK people tend to eat them as they are but in Mediterranean the olives are likely to be marinated using family recipes.

Green olives are also the most likely to be stuffed with a whole range of fillings including garlic, anchovy, pepper, almonds, cornichons (tiny baby gherkins – delicious and very cute).

Black olives are fully ripe, have a high oil content, a mellow flavour and soft flesh. Normally, they are simply washed and preserved in brine.