Why are some olives black and others green?

All olives are green and firm initially. It is as they ripen that they take on a yellow-green color, then reddish pink, then purple, and finally completely black. The more they mature, the more they also soften and the more their amount of oil increases. During this maturation process, the compounds polyphenols which give the strong notes of bitterness and the spiciness of the olives are decomposed and considerably diminished; so the oil quality therefore also decreases. The greener the olives, the less oil they contain, but best quality the oil is.

The nutrition corner

Polyphenol, is a generic term that describes a group of phytochemicals found in olive oil and other natural substances. Several of these polyphenols demonstrate antioxidant properties and anti-inflammatory. The positive effects of polyphenols are the subject of much medical research, especially with regard to the prevention of cardiovascular disease, cancer, and Alzheimer's disease.


The typical flavors of green, unripened olive are described as herbaceous, mint, artichoke, green tea, nettle, cinnamon and green banana, which turn into flavors of berry, hazelnut, butter, ripe bananas and tropical fruits specific to the olive variety.

Green table olives are harvested firm green and marinated in a salted brine solution. Soft black table olives are harvested black and marinated in the same way as green olives. 

Did you know?

The "Californian process" for making firm black table olives is to harvest them green, before they soften, and then oxidize them in a lye solution (aqueous alkaline solution) to make them black. 

See the publication called "Beware of Fake Black Olives" for more information.

The chemistry behind it all

The quantity of polyphenols measured has become an important quality indicator given that the higher the number of polyphenols in an oil, the more it will be antioxidant and will have positive effects on health. So the more, the better.

An amount of 300 polyphenols is considered to be low, while 500 and above is high. Some oils can have up to 800 polyphenols, but they are often considered too bitter for consumers.   

In conclusion

The greener and more unripe the olives, the more polyphenols they contain which have positive effects on health. The pronounced bitterness taste can be used as an indication of a high amount of polyphenols. It is important to taste olive oils before buying them, since the quality of the oil can be measured not only chemically, but also by taste. Remember the qualities of a good oil on your next tasting: bitter, fruity, and peppery, the three characteristics accepted by the International Olive Council, the European Union, and the United States Department of Agriculture.


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