Green, Black, Oolong Tea Differences

Green, Black or Oolong Tea

All “true” tea comes from the Camellia sinensis bush, but the way it’s processed determines whether the end product will be green, black or oolong tea.

Black Tea
To make black tea, the freshly picked tea leaf is deliberately exposed to the air, left on trays in the sun to wither and dry for 18-24 hours. Then the leaves are broken and allowed to ferment for a time, before being fired.

Oolong Tea
Making oolong tea is similar, although the withering and fermenting processes are shorter, resulting in a partially-fermented leaf.

Green Tea
But green tea leaf isn’t fermented at all – in fact, just the opposite! The tea leaves are steamed almost immediately after picking in order to stop the fermentation process, after which they are rolled and dried. So black tea is fermented, green tea is unfermented and oolong is somewhere in between.

To Ferment or Not to Ferment?
Whether or not the tea leaf is fermented has a great effect on the catechin content of the resulting tea. In green tea, the catechins make up about 15-30% of the dry weight of the leaves, compared to just 8-20% of oolong and a miserly 3-10% of black tea.

Why is the catechin content so much lower in black tea? The minute a tea leaf is plucked, an enzyme called polyphenol oxidase combines with oxygen and begins to change the catechins into compounds called theaflavins and thearubigens. This process is encouraged in the manufacture of black tea. Not only are the tea leaves left to wither in the sun for 18-24 hours, they are also twisted and broken to accelerate the process of converting catechins into theaflavins and thearubigens. These compounds are responsible for the distinctive taste, aroma and dark color of black tea. And while they do have some health benefits, they don’t have the same wide-ranging antioxidant and disease-fighting prowess as the catechins.

The Number One Rule in Green Tea Processing
Every green tea processor knows that, above all, they must protect the catechins from the effects of polyphenol oxidase -- to preserve the look, taste and health benefits of this amazing beverage. They do this by steaming or pan-firing the tea leaves just as soon as they are plucked, to inactivate the enzyme. This means the tea leaves must be rushed to the manufacturing plant as soon as they are picked, and care must be taken not to break or bruise the leaves in the process.

Then, once the leaves have been steamed, they can safely be rolled, twisted, dried and packaged without obliterating the catechins. Still, even after the leaves have been processed and packaged, the catechins in green tea can be destroyed if exposed to oxygen for too long. That’s why you should always keep your green tea in an airtight container, even if it comes in tea bag form. Remember: Oxygen is the catechins’ worst enemy.

Nadine Taylor, M.S., R.D. presents GreenTeaLibrary.com, the most comprehensive collection of scientific information describing the many health benefits and properties of green tea.