Tea is about the most widely consumed beverage in the world, only surpassed by water. It is got from the leaf of the tea tree thea sinensis (Camellia sinensis) which has its origin in Asia. History traces the origin of tea to China about 4,500 years ago, discovered by one of the Chinese emperors by accident. It is said to have reached Europe in the early 17th century and got to America only later in that same century. Today tea is consumed all over the world with a sizeable proportion of total world consumption taken up by the United Kingdom.
The biggest producers are China, India, Kenya, Sri Lanka, Turkey, Indonesia, Vietnam, Iran, Japan, Argentina, Taiwan and Pakistan.
Tea contains Caffeine, Theobromine, Theophylline, Tannin/Flavonoids (anti-oxidants), Amino acids, Minerals, Pigments and Carbohydrates.
Caffeine in tea is about half the quantity in the same amount of coffee, caffeine is a known stimulant, just like theobromine.
Though several varieties of tea exist based on geographical origin, there are six main types as shown below. Herbal tea is not produced from the tea tree –camillia sinensis and so it is in the real sense not TEA.
The types listed below are determined by geography, growing and processing and so differ to some extent in health benefits. The health benefits of tea are due to the anti-oxidants it contains.
1. Black tea
Like explained above, the type of tea is determined by the geography, growing and processing. Black tea is the most popular type of tea in the world and contains the highest level of caffeine among the different types of tea.
Processing involves complete withering of the leaves (allowing the leaves dry by losing water) and complete oxidation (reaction of oxygen and the chemicals in the leaf cells). The process of oxidation changes the colour of the leaves from green to black/brown, hence the name black tea.
Black tea has less anti-oxidants than the other types of tea and so of less health benefits. The caffeine is responsible for the alertness of drinking black tea while the Amino acid, Theanine is responsible for the anti-stress effect.
One of the anti-oxidants in tea is Tannin which gives tea its dry feeling in the mouth and the bitter after-taste. The more the exposure of the tea leaves to air for oxidation, the more the release of Tannins in the tea. The latter can give headache, hence the headache in some people after drinking concentrated black tea.
2. Dark tea
Dark tea is darker than black tea and said to be of high medicinal value but there is no empirical evidence for this. However it is seen as a special delight in China. The leaves are allowed to wither completely like in the processing of black tea followed by complete oxidation. After oxidation, the leaves are compressed into various shapes and made to age for months or years depending on what the processors wants to achieve. Durng the aging period, the compressed tea is exposed to  bacteria and fungi for fermentation.
Dark tea is produced from tea grown in a certain region in China. Until the mid nineties, dark tea was not allowed into the USA.
Dark tea is low in caffeine, theobromine and theophylline and does not have dry feeling in the mouth. It has some anti-oxidants like black tea but loer tha green tea/yellow tea/hite tea.
It is said to aid digestion
3. Oolong tea
Oolong tea is between black tea and green tea; the leaves are allowed to wither partially and the oxidation is also only partial. Therefore it has less caffeine than black tea and dark tea but more than green tea.
Because of the processing method, it has less anti-oxidants (hence less Tannin) in concentration than green tea but more than black tea and dark tea.
4. Green tea
The processing of green tea is very different, the leaves are neither allowed to wither (so retains its water content and the green colour of tea leaves, hence the name) and there is no oxidation.
Consequently, green tea has less caffeine than black tea, dark tea and oolong tea. Conversely, it is very rich in anti-oxidants which are responsible for the health benefits of green tea.
Green tea protects the heart, lowers cholesterol level and has anti-aging effects
5. White tea
White tea is processed exactly like green tea but it is made from young tea leaves and buds, consequently it is very low in caffeine but high in anti-oxidants; the concentrations of theobromine and theophylline are also low. Theobromine is a stimulant like caffeine and also a diuretic, so the consumer urinates more in volume and frequency; this can happen with black or dark tea.
Like Green tea, white tea protects the heart, lowers cholesterol level and has anti-aging effects.
6. Yellow tea
Yellow tea is said to be a variety of green tea, it is allowed to wither slightly but no oxidation is allowed. It is then covered wit with cloth or mat and steamed. The steaming is said to convert the leaves to slight yellow colour, hence the name.
It is low in caffeine but rich in anti-oxidants like green tea.
Like Green tea, yellow tea protects the heart, lowers cholesterol level and has anti-aging effects.
7. Herbal tea
There is nothing like herbal tea in the real sense as herbal teas are not produced from the tea tree—Camellia sinensis. It is only a sales gimmick; there are herbal beverages or herbal drinks. They do not contain caffeine nor theobromine nor theophylline but like most plant products they contain some anti-oxidants.
Herbal “teas” or better called Herbal drinks include Moringa drink, Ginseng drink and Chamomile or Camomile tea.
8. Conclusion
The tea you want to drink depends on you; for alertness and relaxation, go for black tea. But remember the possible headache and increased passage of urine.
For some alertness and relaxation combined with some additional health benefits, go for green tea/white tea/yellow tea.
If you are sure of the content of herbal tea, no problem.
I now drink green tea, yellow and white teas are not readily available.

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