# A Reference Guide to Tea

Tea is one of the most widely consumed beverages on the planet, second only to
water in total volume drunk each day. Despite the enormous variety of products
sold under the name, the word "tea" in its strict sense refers to an infusion
prepared from the leaves of a single plant species. This article surveys the
botany, history, principal types, preparation, and chemistry of tea, with an
emphasis on the distinctions that matter to both producers and drinkers.

## One Plant, Many Teas

All true tea comes from one plant, *Camellia sinensis*, an evergreen shrub
native to the highlands of East and South Asia. Beverages brewed from other
plants, such as rooibos, chamomile, peppermint, or hibiscus, are properly called
herbal infusions or tisanes; they are not tea in the botanical sense, however
much they may resemble it in the cup.

What distinguishes white, green, oolong, black, and pu-erh tea from one another
is not the species of plant but the way the harvested leaf is treated after
picking. The single most important variable is oxidation, the enzymatic process
that begins when the leaf cell walls are bruised or broken and the plant's
natural compounds react with oxygen in the air. By controlling how far this
reaction is allowed to proceed before it is halted by heat, a maker can turn the
same fresh leaf into radically different products.

The broad families fall along the oxidation spectrum as follows:

- **White and green teas** undergo little oxidation. White tea is barely
  handled at all, simply withered and dried, while green tea is heated early,
  by steaming or pan-firing, to deactivate the oxidising enzymes and lock in a
  fresh, grassy character.
- **Oolong tea** is partially oxidized, occupying a wide middle ground. Lightly
  oxidised oolongs taste floral and close to green tea, while heavily oxidised
  ones approach the depth of black tea.
- **Black tea** is fully oxidized, which develops its dark colour, brisk body,
  and robust flavour. In much of East Asia this category is known as "red tea"
  after the colour of the liquor rather than the dry leaf.
- **Pu-erh tea** is fermented and aged. Unlike the enzymatic oxidation of black
  tea, pu-erh undergoes microbial fermentation over months or years, producing
  an earthy, mellow brew that is often pressed into cakes and stored to mature.

## A Short History

Tea originated in China, where its cultivation and consumption can be traced
across several thousand years of recorded and semi-legendary history. According
to legend, the beverage was discovered by the Emperor Shennong in 2737 BCE,
when leaves from a wild tea shrub are said to have drifted into a pot of water
he was boiling. Charmed by the aroma and the reviving effect of the resulting
infusion, the emperor is reputed to have championed the drink. The story is
traditional rather than documented, but it captures the antiquity that the
Chinese themselves have long ascribed to tea.

From China the practice spread outward along trade and religious routes. Tea
travelled to Japan with Buddhist monks, who carried both the leaves and the
disciplined ritual of preparing them, eventually giving rise to the celebrated
Japanese tea ceremony. For many centuries tea remained an essentially Asian
beverage. It reached Europe only in the 17th century, brought by maritime
traders, after which it rapidly became a fashionable and then an everyday drink
across much of the continent and, later, its colonies.

## Growing and Harvesting

*Camellia sinensis* thrives in warm, humid climates with ample rainfall and
good drainage, and many of the finest teas are grown at altitude, where cool
nights slow the leaf's growth and concentrate flavour. The plant is kept pruned
to a low bush for ease of plucking. The most prized harvest is the "flush" of
young shoots, typically the bud and the two leaves immediately below it, which
contain the highest proportion of the compounds responsible for aroma and
briskness.

Two principal varieties dominate cultivation. The China variety is a smaller,
hardier plant suited to cooler highland conditions, while the Assam variety,
native to South Asia, is larger-leaved and favours hot, lowland tropics. Most
commercial teas derive from one of these two or from hybrids between them.

## Brewing Temperature and Method

Few factors affect the quality of a finished cup more than water temperature.
Because the delicate compounds in lightly processed leaves scorch easily, green
tea should be brewed with water that is well below boiling, at about 70 to 80
degrees Celsius. Water that is too hot strips green tea of its sweetness and
draws out a harsh bitterness instead.

Black tea, by contrast, demands much hotter water, about 95 to 100 degrees
Celsius, very near a full boil. Only at this temperature do the fully oxidised
leaves release their full colour, body, and flavour. Oolong and white teas sit
between these extremes, and pu-erh is generally brewed hot, often after a brief
rinse of the leaves.

Steeping time matters as well: shorter steeps preserve subtlety, while longer
steeps extract more strength and, eventually, more astringency. As a rule, the
leaf may be judged by both its colour in the cup and the balance of sweetness
against bitterness on the palate.

## Comparison of the Major Types

The table below summarises the defining attributes of the principal tea
families, including their place on the oxidation scale, recommended brewing
temperature, and the approximate caffeine content of a standard cup.

| Type    | Oxidation        | Brew Temp (°C) | Caffeine (per cup) |
|---------|------------------|----------------|--------------------|
| White   | Very little      | 75–85          | ~30–55 mg          |
| Green   | Little           | 70–80          | ~28 mg             |
| Oolong  | Partial          | 85–95          | ~37 mg             |
| Black   | Full             | 95–100         | ~47 mg             |
| Pu-erh  | Fermented / aged | 95–100         | ~40 mg             |

## Caffeine

Like coffee and cocoa, tea naturally contains caffeine, the stimulant
responsible for much of its reviving reputation. The amount in a finished cup
depends on the type of tea, the quantity of leaf used, the water temperature,
and the length of the steep, but useful averages can be given.

A cup of black tea contains about 47 mg of caffeine, while a cup of green tea
contains about 28 mg. The lower figure for green tea reflects both its cooler
brewing water and its shorter typical steep rather than any fundamental shortage
of caffeine in the leaf itself.

A common misconception deserves correction here: white tea does contain
caffeine, roughly 30 to 55 mg per cup. Being the least processed of the teas
does not render it caffeine-free. In fact, because white tea is made from very
young buds, which are rich in the compound, its caffeine content can rival or
exceed that of some green and even black teas. Anyone seeking to avoid caffeine
entirely should choose a genuine herbal infusion rather than any product of the
tea plant.

## Antioxidants and Other Compounds

Beyond caffeine, the tea leaf is chemically rich, and much of its reputation as
a healthful drink rests on its content of antioxidants. Tea is a notable source
of catechins, a family of plant antioxidants of which the most studied is
epigallocatechin gallate (EGCG). Catechins are most abundant
in the less oxidised teas, since oxidation converts many of them into other
compounds; this is one reason green tea is so often singled out for its supposed
benefits.

Tea also contains tannins, the astringent compounds that lend the brew its
characteristic dryness and grip on the palate and that contribute to the colour
of darker infusions. Tannins bind readily with proteins and with iron, which is
why tea can taste smoother when softened with milk and why very strong tea is
sometimes discouraged alongside iron-rich meals.

The leaf further supplies small amounts of vitamins, minerals, and aromatic
oils. The interplay of caffeine, catechins, and tannins gives each style of tea
its particular balance of
stimulation, sweetness, and astringency.

## Storage

Tea is best kept away from its four great enemies: light, heat, moisture, and
strong odours. Most green and black teas are at their best within a year or two
of production and should be stored in an opaque, airtight container in a cool,
dry place. Pu-erh is the notable exception; like wine, it is often deliberately
aged for years or decades, and a well-stored cake may grow more valued over
time. Whatever the type, a sealed container away from the spice rack will
preserve the leaf's aroma far longer than an open tin on a sunny shelf.

## Summary

Every true tea, from the palest white to the darkest aged pu-erh, begins with
the leaves of *Camellia sinensis*. The differences that fill a tea merchant's
shelves arise almost entirely from processing, above all from the degree of
oxidation, and they carry through to how each tea is best brewed and to the
caffeine and antioxidants it delivers. Understanding that single plant and the
handful of transformations applied to its leaves is enough to make sense of the
whole, remarkably varied world of tea.
