The manufacturing methods used in making black, oolong, and green tea not only alter the taste, aroma, and quality of the finished brew, but also change the way tea can affect your health. That’s because unfermented green tea leaves contain much larger amounts of a group of potent health promoters called polyphenols, which are chemically changed during the fermentation of black and oolong teas.
Polyphenols are naturally occurring chemical compounds found in certain fruits and vegetables, potatoes, garlic, and a few other foods. A subgroup of the poly-phenols-the catechins (pronounced “CAT-i-kins”) - are particularly powerful disease fighters and potent antioxidants that have a host of beneficial effects, from preventing food spoilage to halting the progression of cancer. Catechins are found in wine, Ginkgo biloba leaves, and pine bark, but appear in the greatest quantity in fresh tea leaves.
The way the tea leaf is processed greatly affects the catechin content of the finished tea. For example, the catechin content of green tea is an impressive 15-30% of the tea’s dry weight. Oolong, on the other hand, contains just 8-20% catechins, while black tea brings up the rear with only 3-10%. What happens during the processing of oolong and black teas that “kills off” so many catechins? Well, it all begins in the tea field, as soon as the leaf is plucked from the plant.
Tea leaves contain an enzyme called polyphenol oxi-dase. When the leaf is plucked, this enzyme combines with oxygen (a process called oxidation) and begins to change the structure of the catechins. In the manufacturing of green tea, the number one goal is to prevent as much oxidation as possible. Some, of course, is inevi-table. But the application of heat inactivates the enzyme, so the trick is to get the freshly plucked leaf from the field to a heat source as quickly as possible. That’s why time is of the essence in green tea manufacturing: Once the leaf has been plucked, the race begins!
When manufacturing green tea, growers rush the leaves from the field to the factory, being careful not to bruise or break them, since that would speed up the oxidation process. At the factory, the leaves are steamed, pan-fired, or roasted to stop the enzyme-driven changes and preserve as many catechins as possible. Then they are rolled, twisted, and dried thoroughly. The beverage made from these tea leaves is clear light green to light golden brown in color, with a refreshing, slightly bitter, but smooth taste.
Black tea undergoes a completely different kind of processing. The leaves are plucked, but instead of being rushed to a heat source, they are spread on trays or racks and left to wither in the sun for 18-24 hours. During this time, one-third to one-half of their weight evaporates. Then the leaves are rolled and twisted in order to break down the cell walls and accelerate the oxidation of the catechins (exactly the opposite of what is done in green tea manufacturing).
Green tea is produced in a four-step process:
- Steaming or pan-firing immediately after harvesting to kill the fermentation enzymes. This also makes the leaves soft and pliable.
- Rolling, either by hand or machine, on heated trays to reduce the moisture content.
- Twisting, which helps adjust the water content.
- Drying, during which the leaves are rolled, shaped, and styled.
Withering and twisting causes leaves to ferment, and during this process, the catechins are oxidized into more complex compounds called thearubigens and theaflavins. These compounds give black tea its characteristic color, aroma, and taste. In the final stage, the leaves are fired, which stops the fermentation and reduces the moisture content. Black tea produces a dark reddish-brown brew with a bittersweet taste and a rich, appealing aroma. The longer the leaves have been fer-mented, the darker the color and the less astringent the resulting tea.
Processing Black Tea
As with green tea, the making of black tea requires four major steps:
- Withering, in which leaves are spread on trays in the sun to soften and dry for 18-24 hours.
- Rolling, which breaks apart the cells in the leaf and releases enzymes which will act on the catechins.
- Fermenting, when enzymes and oxygen transform catechins into thearubigens and theaflavins.
- Firing, which stops the fermentation process and dries the leaves.
Keeping the Polyphenols in Green Tea
Protecting the polyphenols from oxidation is the most important part of the green tea manufacturing process. The leaves must be picked and rushed to the processing plant, where the oxidizing enzymes are stopped dead. The next step depends on where the leaves are being processed:
- In China, the tea leaves are rapidly pan-fired or roasted over wood or charcoal.
- In Japan, they are steamed for 20-50 seconds in large rotating cylinders.
- In India, they are rotated in heated cylinders for 7-10 minutes.
Then the tea is twisted and dried until the moisture content is reduced to about 3%. If done correctly, the processed green tea should be light yellow-green with absolutely no oxidation of the polyphenols.
Whether the leaves are steamed, pan-fired, or rotated in heated cylinders doesn’t seem to matter as far as taste or quality is concerned. The important thing is to stop the action of the oxidation of the polyphenols and any good heat source will do that. Roasting, how-ever, gives a distinctly smoky, nut-like flavor that makes green tea taste like a completely different beverage.
To make oolong tea, manufacturing methods from both green and black tea are combined. The fresh leaves are spread out in large, flat baskets and left to wither in the sun for four to five hours. These baskets are shaken every so often to bruise the edges of the leaves, ensuring that more oxidation will occur at the edge of the leaves than in their centers. When the leaves are about half fermented, they are fired to stop the process and reduce moisture content. Then they are rolled, twisted, and dried.
The Wondrous Catechins
For thousands of years, the Chinese have claimed that brewing tea and drinking tea with traditional Chinese teapot is good for your health, both mentally and physically. But only recently have scientists been able to investigate these claims by isolating the components of tea and putting them to the test in laboratory experiments.
Curiosity about the effect of green tea on human health was first aroused in the 1970s. Epidemiologists noticed that people living in the Shizuoka Prefecture, an area in central Japan where green tea is grown and consumed in great quantities, had a much lower rate of death from stomach cancer than people living elsewhere in Japan. This low death rate was very significant because stomach cancer was (and still is) the most prevalent form of cancer in Japan.
Once scientists began to study the people who lived in the Shizuoka Prefecture, they were surprised to discover that, not only did they die less often of stomach cancer, their death rates from all types of cancers were significantly lower. Curious and excited, the scientists conducted exhaustive studies of the population. The only major difference they could find was the people who lived in the Shizuoka Prefecture drank significantly more green tea than people living in areas with higher rates of cancer.
Polyphenols? Flavonoids? Catechins?
As you read about green tea in books and maga-zines, you’ll come across several related health terms. Although often used interchangeably, they have different meanings.
Polyphenols are naturally occurring compounds that act as powerful antioxidants.
There are many types of polyphenols, including the flavonoids found in green tea, fruits, and vegetables.
(The flavonoids are also called bioflavonoids.)
Catechins are a particular kind of flavonoid found in tea, especially green tea. They’re sometimes called green tea polyphenols.
Tea researchers usually talk about five types of cate-chins:
gallocatechin (GC)
epicatechin (EC)
epigallocatechin (EGC)
epicatechin gallate (ECg)
epigallocatechin gallate (EGg), the most potent of the catechins
Everybody drinks tea in Japan, and most of it is green.
But they really drink it in the Shizuoka Prefecture, since acres and acres of tea grow right there, practically in the backyard. This easy accessibility makes for almost continual sipping throughout the day. The water is always boiling, and just-picked tea leaves are often added to the teapot to refresh the brew.
When studying black tea drinkers around the world, scientists didn’t see the same dramatic cancer-protective effects as they saw in Shizuoka. But why not? they won-dered. What did green tea have that black tea didn’t have? The answer was clear-more catechins. Catechins make up as much as 30% of the dry weight of green tea leaves, but only 3-10% of black tea. So the scientiss went back to their laboratories determined to prove (or disprove) the theory that the catechins in green tea were the miracle substance that could help prevent cancer.
In order to use the green tea leaf with maximum efficiency in tests on laboratory animals, researchers used a scientific process to extract its catechins and condense them into a powdered form. This powder could then be mixed with the food or drinking water or diluted and injected into the skin. Since the catechins were first isolated and tested, thousands of studies of their physiological effects have been conducted. And the results have been nothing short of astounding. As you will see in the chapters to come, green tea protects against many of the most dangerous and deadly diseases plaguing humankind today. And no matter how much green tea you may drink, there are literally no adverse side effects.
Other Health-Promoting Ingredients in Green Tea
In addition to the catechins, green tea contains these health promoters:
Flavonols-which (like the catechins) are a subgroup of the flavonoids known for their strong antioxidant properties. They help trap and destroy free radicals, singlet oxygen, and peroxides, keeping them from destroying body tissue. They also work together with vitamin C to help strengthen blood vessel walls.
Vitamin C-which helps to reduce stress, fight infection, and strengthen the immune system.
Vitamin B complex - which aids in the metabolism of carbohydrates.
Vitamin E-which has antioxidant properties and helps retard aging.
Fluoride-which helps to harden tooth enamel, thus preventing cavities.
But before we explore the “green tea miracle” any further, let’s take a look at the origins of tea itself and how it spread throughout the world as a comforting and health-promoting beverage.
