Tea Science

Botanical: Camellia Thea (Sinensis)
Family: Camelliaceae
Synonyms: Thea Sinensis; Thea Veridis; Thea Bohea; Thea Stricta Jassamica; Camellia Theifera
Part Used: Dried leaf
Habitat: Assam; cultivated in Ceylon, Japan, Java, and elsewhere where climate allows

Description

* A small evergreen shrub cultivated to a height of 7 to 8 feet, but growing wild up to 30 feet high.
* Bark is rough and gray.
* Leaves are dark green, lanceolate or elliptical, on short stalks, blunt at apex, base tapering, margins shortly serrate, young leaves hairy, older leaves glabrous.
* Flowers solitary or two or three together on short branchlets in the leaf axils, somewhat drooping, on short stalks with a few small bracts, 1 to 1 1/2 inches wide; sepals five, imbricate, slightly united below, ovate or rounded, blunt smooth, persistent; petals usually five or up to nine, unequal, strongly rounded, concave, spreading, white, caducous; stamens indefinite, adherent to petals at base in two rows, filaments fiexuose, half the length of petals; anthers large, versatile; ovary small, free, conical, downy, three-celled with three or four pendulous ovules in each cell; styles three distinct or combined at base, slender simple stigmas.
*Fruit is a smooth, flattened, rounded, trigonous three-celled capsule; seed solitary in each cell; size of a small nut.

It was formerly supposed that black and green tea were the produce of distinct plants, but they are both prepared from the same plant. Green tea is prepared by exposing the gathered leaves to the air until superfluous moisture is eliminated when they are roasted over a brisk wood fire and continually stirred until they become moist and flaccid. After this it is passed to the rolling table, and are rolled into balls and subjected to pressure which twists them and gets rid of the moisture. They are then shaken out on flat trays, again roasted over a slow and steady charcoal fire, and kept in rapid motion for an hour to an hour and a half, until they assume a dullish green color. After this they are winnowed, screened, and graded into different varieties. With black tea, the gathered leaves are exposed to the air for a longer period, then gathered up and tossed until soft and flaccid, and after further exposure, roasted in an iron pan for about five minutes. After rolling and pressing, they are shaken out, exposed to the outer air for some hours, re-roasted for three or four minutes, re-rolled, spread out in baskets and exposed to the heat of a charcoal fire for five or six minutes and then rolled for the third time and again heated, and finally dried in baskets over charcoal fires, from which process they become black in color. China is the great tea-producing country, over four million acres of ground being devoted to its cultivation.

Constituents - Caffeine (theine), tannin (10 to 20 per cent gallotannic acid), boheic acid, volatile oil, aqueous extract, protein wax, resin, ash and theophylline.

Medicinal Action and Uses - Stimulant, astringent. Caffeine exerts a decided influence over the nervous system, generally evinced by a feeling of comfort and exhilaration; it also causes unnatural wakefulness when taken in quantity. Taken moderately by healthy individuals it is harmless, but in excessive quantities it will produce unpleasant nervous and dyspeptic symptoms, the green variety being decidedly the more injurious. Tea is rarely used as a medicine, but the infusion is useful to relieve neuralgic headaches.

Tea Chemistry
When you pour boiling water over black or oolong tea leaves you are releasing the results of some truly wonderful chemical developments that occur during the processing, which is known as oxidation. Green tea is not oxidized. The three most important chemical substances in the fresh tea leaf are caffeine, aromatic or essential oils, and polyphenols (popularly but incorrectly known as tannins). The essential oils are important constituents of the aroma of the beverage. These substances are sometimes known as volatiles, which means that they will totally evaporate in strong heat. When tea is kept a long time, these disappear, reducing aroma. Both tannins and oils aid digestion by stimulating peristalsis of the intestinal tract. There is some evidence that tea counteracts the effect of fats by emulsifying them in the digestive tract. The polyphenols are the most interesting elements and the ones which do the greatest good for human health.

During manufacture, black and oolong tea undergo their oxidation process. Spread out in a cool place, the leaves absorb oxygen, which creates chemical changes. This process should correctly be called oxidation, for the leaves are worked on by oxygen rather than fermented by microorganisms. The polyphenols, about thirty altogether, account for nearly a third of the soluble matter in the fresh tea leaf. During the oxidation process about a third of the total amount is oxidized into more complicated oxidized products such as theaflavin. Therefore, after process the tea contains two kinds of polyphenols, oxidized and unoxidized (natural polyphenols). The latter, released in the beverage, (the astringent, "puckery" feeling in the mouth when you drink tea) stimulates the salivary glands, which is why tea is a thirst quencher. The unoxidized polyphenols provide the pungency, while the oxidized ones give the tea its color and flavor. The higher the degree of oxidation the more color and less pungency a tea has. Green tea, which does not undergo oxidation, has more natural unoxidized polyphenols, and tea polyphenols, though popularly known as tannins, are not as widely believed, the tannic acid used in leather preparation. In fact, they are not tannins at all. With some chemical and functional similarity, they became known by this name long before modern methods of chemical analysis made it possible to distinguish the two.

Here we have run into another of those name confusions that seem to haunt tea. There's more. Three-fourths of the tea polyphenols are catechins which are part of the chemical group flavanols deed have something to do with flavor, as distinct from either aroma or astringency). At least six catechins have been isolated. We might make a summary outline like this:

Polyphenols (compounds with two or more phenolic hydroxyl groups)
Flavanols (one kind of polyphenol)
Catechins (the name for flavanols in tea)

Reports on the health benefits of these substances may use any of the three. Often no distinction is made between the terms "catechins" and "polyphenols," and in many cases the two are used interchangeably. Both oxidized and unoxidized polyphenols may be beneficial. Now let's see what happens in the polyphenol oxidation process. At the tea factory, the freshly picked leaves sit until they have become soft and limp as a result of water evaporation. Then they are rolled to break down the membranes and bring the juices containing polyphenols in contact with the enzyme polyphenolase (polyphenol oxidase) which catalyzes the oxidation of the polyphenols by oxygen in the atmosphere. The product resulting from this process, together with other constituents, accounts for the unique flavor and rich, deeper color of black and oolong teas. The action of the enzyme, and therefore the oxidation process, is eventually stopped through heating, but these compounds remain in the dried prepared leaves waiting for the boiling water to dissolve them.

Vitamin C and Other Nutrients
In China it is widely stated that green tea is a source of vitamin C. Since this vitamin is destroyed by heat and tea is made in hot water, this statement seems contradictory. Recent tests in China found that heat destruction does occur, but not in tea. Something in tea, as yet undetermined, apparently helps stabilize vitamin C. The amount of vitamin C varies greatly depending on growing conditions, the age of the leaves at picking, and how long they have been stored. Japanese tests found that tea stored three years had lost all its vitamin C. According to Chinese calculations, typical green tea made with three grams (one teaspoonful) of dry leaves to a cup should yield about six milligrams of the total content of vitamin C in three infusions in water at 158 to 212 degrees Fahrenheit (70 to 100 degrees centigrade). Eighty-five percent of the vitamin C is released in one five minute infusion at 176 degrees Fahrenheit (80 degrees centigrade). As for black tea, authorities have long believed that almost all its vitamin C is destroyed during oxidation. Tea also contains vitamins B, K, and P, and niacin, folic acid, and manganese, but in such small amounts as to be negligible. A cup of black tea has 58 milligrams of potassium.

The three main components of the tea leaf are caffeine, polyphenols, and aromatic or essential oils. Here in brief is what they do:

* Caffeine in moderate quantities, stimulates the central nervous system and promotes blood circulation. It stimulates the process of elimination and acts as a diuretic promoting better kidney function. There is some evidence that regular tea drinkers have a lower incidence of kidney ailments and gallstones. Some researchers have even claimed that it also helps the body excrete radioactive strontium 90, the element which entered the food chain from atmospheric fallout from nuclear bomb testing.
* Polyphenols isolated from tea may act as an anti-cancer agent in that they have an anti-mutant factor which helps cell DNA to reproduce itself accurately rather than in mutated forms which might lead to cancer. Medicines made from tea polyphenols have become part of the treatment for nephritis, chronic hepatitis, and leukemia in China.
* Essential Oils (sometimes called aromatic oils, sometimes volatiles because they totally evaporate) are formed in the tea leaves as they grow. They account for the aroma of the beverage. These substances also aid digestion and help emulsify fat. Green tea has more essential oils than the more highly processed black tea. That is why black tea has less aroma. Jasmine tea is said to have the greatest amount, ranging from .06 percent to .4 percent. The most elementary reason tea has saved millions of lives over two thousand years is simply because making it requires boiling water, which kills disease germs. In areas of poor water quality, every cup of tea was boiled.

Tea and Caffeine
Tea leaves typically contain from 5 percent caffeine by dry weight. This is irrelevant, however, because no one sits down and eats a bowl of dry tea leaves. If a person did, he or she would intake a massive amount of caffeine - nearly 15,000 mg, for each pound consumed. The real question is how much caffeine does a cup of tea contain? Once again, the answer is somewhat complicated. Caffeine is a water-soluble molecule. The amount of caffeine that dissolves into the water depends on the amount of dry tea used to brew a cup.

If a person uses the traditional two grams of tea per 5.5 ounces of water, the potential caffeine content for a cup of tea ranges from 60-100 mg. Still not confused? Consider this - the amount of caffeine present in the cup also depend on the steeping time, leaf size and the temperature of the water. For example, people steep some green teas for very short periods of time and with relatively cool water (compared to the near boiling water used to extract black tea flavors). Therefore these green teas seemingly have less caffeine because they are in less contact with the water, although the tea by dry weight may contain the same amount of caffeine. This is no reason for the general misconception that green tea always contains less caffeine than black or oolong lea. Here's more fuel for the fire of confusion. The caffeine content in dry tea leaves is affected by a variety of factors, including processing methodology (especially firing) soil chemistry, altitude, and harvest season.