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Green, Black or Oolong?
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.
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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.
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