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plantings were started in Ceylon (now Sri Lanka)

during the 1870s. The cultivation of tea has since

spread to other Asian countries, such as Turkey,

Iran, Taiwan, Bangladesh, and Malaysia. In the late

nineteenth century, cultivation of tea spread beyond

Asia to Africa and South America. Tea was first intro-

duced into Malawi in 1886 and into East Africa at the

beginning of the twentieth century. Production of tea

in the former Soviet Union began on a large scale in

1892. Today, tea is grown in over 30 countries. The

most northerly region in which tea is grown today is

Georgia, in south Russia, and the southernmost is

South Africa, and the Argentine in South America.

Classification

0003 The tea plant, Camellia sinensis (L.) O. Kuntze, is the

only important economic species of the family Thea-

ceae. Two botanical varieties have been recognized.

China Teas (

Camellia sinensis

var.

sinensis

)

0004 These teas are produced from slow-growing, dwarf

trees (which grow to a height of 4–6 m if unattended),

with small, erect, comparatively narrow, markedly

serrated, dark green leaves which are smooth with a

matt surface; the flowers are borne singly. The plant is

relatively resistant to cold and, as a result, the variety

is found in the more temperate producing regions

such as China, Japan, the former Soviet Union,

Turkey, Iran, and the northern, higher-altitude grow-

ing areas of India. It is known to produce delicately

flavored tea when grown at high altitudes; it is, how-

ever, low-yielding, especially at very high altitudes,

such as Darjeeling.

Assam Teas (

Camellia sinensis

var.

assamica

)

0005 This variety is faster-growing and taller (12–15 m

unattended) than the China variety with larger

glossy elliptical leaves; flowers are found in clusters

of 2–4. This variety is less resistant to cold than the

China type and, as such, can only survive at high

altitudes near the Equator. In general, it is a much

higher-yielding plant than the China type, and pro-

duces a less delicately flavored beverage.

0006 Numerous hybrids between China and Assam

types are known. There is evidence that C. irrawa-

diensis was hybridized with C. sinensis var. assamica

to produce the uniquely flavored Darjeeling tea. As

tea is largely cross-pollinated, and much of the com-

mercial crop is raised from seed, the crop is very

heterogeneous.

0007 The term ’jat’ is used to indicate seed derived from

different districts or plantations or to separate types

on the basis of foliar characteristics.

Types of Processed Tea

Fermented or Black Tea

0008Black teas form the major proportion of tea con-

sumed in the western hemisphere. They are produced

by full fermentation and roughly classified as plain or

flavory.

0009Plain black teas are produced and sold on the basis

of the taste characteristics associated with the phen-

olic substances produced during fermentation. These

teas are mainly produced and exported from Africa

(e.g., Kenya and Malawi) and India (Assam). High-

quality plain teas are often known as breakfast teas.

(See Phenolic Compounds; Tea: Chemistry.)

0010Flavory black teas are sold on the basis of their

aroma characteristics and should not be confused

with flavored teas, to which fragrances have been

added. They are primarily manufactured in areas

of relatively high altitude in Sri Lanka and India

(Darjeeling). In Sri Lanka, the very flavory teas are

produced during January and February in the Dim-

bula district, and during August and September in the

Uva district. In these areas, the desired aroma is pro-

duced during cool, clear, dry windy weather with day

and night temperatures of about 20



C and 6–10



respectively. These conditions must last for at least

two consecutive weeks and even slight rain will set the

process back to the beginning. The famed first- and

second-flush Darjeeling flavor is produced under

similar conditions when growth is slow and the plants

are under climatic stress.

Green Tea

0011Green tea is entirely different from black tea in its

preparation. There are no fermentation products and

the leaf remains green. It is generally produced from

var. sinensis. When infused, the liquors are greenish,

pale primrose, or lemon-yellow in color with no trace

of red or brown. Green tea is produced and consumed

mainly in China and Japan. Some is also consumed in

northern Africa. Often, green tea production is a

cottage industry, not only in the countries mentioned

above, but also in other countries such as Malaysia,

Thailand, Vietnam, and Indonesia. This processing is

often undertaken by experienced Chinese tea makers.

(See Tea: Processing.)

0012There are many different kinds of green tea pro-

duced, differing in style and cup characters. Some

varieties of green tea include the following:

0013Sencha, the most widely drunk grade of green tea in

Japan.

0014Kamaira-cha, made from young leaf, but differing

from sencha in that the first process is parching and

not steaming.

5738 TEA/Types, Production, and Trade

.0015 Bancha, made from coarse leaf and stalk.

0016 Gyokuro, one of the finest green teas; it is grown

under complete shade, hand-plucked and hand-

sorted. It has a twisted dark green leaf.

0017 Matcha, a powdered tea also made from shade-

grown leaf.

0018 Tencha, the ceremonial green tea. The beverage is a

suspension of finely ground leaf.

0019 Gunpowder, made in the form of small compact

pellets of Chinese green tea.

0020 Pilo chun, a small-leaved Chinese tea made from

the first spring flush.

Partially Fermented Tea

0021 Typical partially fermented teas include oolong and

pouchong teas. These are partially oxidized so that

their appearance is somewhat intermediate between

that of green and black tea. Pouchong teas have a

shorter fermentation time. They are manufactured

primarily in China and Taiwan. Clones selected for

oolong and pouchong tea production are character-

ized by the ability to impart a strong flowery aroma

to the product. (See Tea: Processing.)

Instant Tea

0022 Instant tea is the water-soluble extract of tea leaf,

usually marketed as a powder, flake, or granule,

either pure or as a part of flavored mixes. Iced

lemon teas are the most popular examples of instant

teas, particularly in the USA. Most instant tea is made

from black tea, but some is made from green tea. It is

manufactured in a number of tea-growing countries,

e.g., Kenya and China, where the starting material

may be fermented leaf that has not been dried.

Flavored Teas

0023 Teas are sometimes scented with various plant essen-

tial oils such as lemon, bergamot, rose, and fragrant

olive which impart sweet floral attributes to enhance

the natural flavor of the tea. Other teas are blended

with flower petals, spices, or dried leaf such as chrys-

anthemum, rosemary, camomile, and peppermint.

Floral flavored teas are mainly consumed in the USA

while herbal teas are popular in continental Europe.

Many of these products are sold through health food

stores and may not contain C. sinensis: the word ’tea’

refers to their method of preparation. These products

are often promoted on health grounds, particularly if

they are caffeine-free. (See Essential Oils: Properties

and Uses.)

Decaffeinated Tea

0024 Decaffeinated tea has been popular in the USA since

its introduction in 1983; however, in the UK the

picture has been slightly different. Until the late

1980s it was primarily retailed through health food

outlets; however more recently a number of specialist

tea companies have launched decaffeinated tea bags

into the mainstream grocery trade with considerable

success.

0025Caffeine is removed from tea by treating it with

one of three organic solvents: methylene chloride,

ethyl acetate, or supercritical carbon dioxide. The

caffeine is dissolved in the solvent and the tea is then

treated to remove most of the solvent. (See Coffee:

Decaffeination.)

Organically Grown Tea

0026Organically grown teas from Tanzania first entered

the UK market in 1989 under the Natureland brand

name from the London Herb & Spice Company.

The tea bags were sold at a 20% premium price

over other speciality teas and at more than double

the price of regular tea bags. Since this time other

organically grown tea products have appeared on

the market. The major producers are India and Sri

Lanka.

0027The attraction to the grower is substantially in-

creased price for the crop and the saving of hard

currency on chemical fertilizers and pesticides. It is

believed that the average transition period from con-

ventional to organic culture is 3 years, allowing time

for chemicals to disperse.

World Production

0028According to statistics compiled by the Inter-

national Tea Committee, tea production over the

past decade (1988–98) increased from 2.48 million

metric tons (mt) to 2.96 million mt. This represents

an average annual rate of increase of 1.9%. The

major producers are listed in Figure 1 along with

their average production for the 1995–97 period

and for 1998, the last year for which figures are

currently available. The 3-year averages have been

included to reveal the trend of changes in pro-

duction through the smoothing of year-to-year

fluctuations.

0029India is currently ranked as the world’s largest

producer of tea, followed by China, Kenya, and Sri

Lanka. Kenya in particular had a record production

for 1998 that represents an increase of over 33.3%

from the 1997 drought-affected crop. Increases in

both yields and planted area are likely to continue

to support strong growth in tea production in Afri-

can countries where the Kenyan output is expected

to increase at an average annual rate of 2.8%.

Malawi, Tanzania, and Zimbabwe are also expected

TEA/Types, Production, and Trade 5739

to increase production significantly. The Intergov-

ernmental Group (IGG) on Tea of the Food and

Agriculture Organization (FAO) of the United

Nations predicts that production in India will

reach 1.02 mt in 2005. Economic reforms and the

national plan to expand tea production in Sri Lanka

could boost production to 285 000 mt, compared to

157 800 mt during the 1995–97 period. Other major

tea-producing countries, including China and Indo-

nesia, should also see significant growth in production,

while in Bangladesh production is forecast to grow

less rapidly.

0030Production expansion programs initiated by

major exporting countries have contributed to pre-

vious increases in output of black tea in recent

years, and the impact of these programs, particularly

as bushes reach optimum production age, may

continue.

0031The total tea area under production has increased

from 1.4 million hectares in 1961 to 2.3 million

100

125

150

175

200

225

250

275

300

0.3

7.8

6.2 5.6 3.9

2.7 1.6 2.5

9.0

1.9

2.5 1.0

6.7

8.9 9.4

0.5 X

Ch Ia In Ir Jp My SL Tw Tk Vt Bu Cm Ky Mw Mr Mz Rw SA Tz Ug Za Zw Ag Br Ec Pr Au PG

2.3

CIS

400

500

600

700

800

900

Region

Asia

Africa

CIS

South America

Oceania

World

1582.7

370.0

14.7

56.8

7.7

2031.9

500.0

0.0

2.3

0.0

595.9

2082.7

370.0

17.0

56.8

7.7

2627.8

Black Tea Green Tea Total

Asia Africa

World production of black and green teas for the year 1995−97

South America

Oceania

Black Tea Green Tea

100

125

150

175

200

225

250

275

300

Ba Ch Ia In Ir Jp My SL Tw Tk Vt Bu Cm Ky Mw Mr Mz Rw SA Tz Ug Za Zw Ag Br Ec Pr Au PG

400

500

600

700

800

900

0.2

8.6

6.3

0.6

6.7 4.7

1.5

1.6 2.5

8.0

1.9 2.4

1.3

6.0

CIS

3.6

Asia Africa

South America

Oceania

Region

Asia

Africa

CIS

South America

Oceania

World

1788.0

445.7

14.4

62.3

7.3

2317.7

641.2

0.0

3.6

0.0

644.9

2429.2

445.7

18.0

62.3

7.3

2962.6

Black Tea Green Tea Total

World production of black and green teas for the year 1998

Black Tea Green Tea

fig0001 Figure 1 World production of black and green teas for the 1995–97 period and 1998 (1000 Mt).

Black and other teas, but not green

teas.

Figures shown are provisional or estimated. CIS: Commonwealth of independent states (former Union of Soviet Socialist

Republics), Ba: Bangladesh, Ch: China, Ia: India, In: Indonesia, Ir: Iran, Jp: Japan, My: Malaysia, SL: Sri Lanka, Tw: Taiwan, Tk: Turkey,

Vt: Vietnam, Bu: Burundi, Cm: Cameroon, Ky: Kenya, Mw: Malawi, Mr: Mauritius, Mz: Mozambique, Rw: Rwanda, SA: South Africa, Tz:

Tanzania, Ug: Uganda, Za: Zaire, Zw: Zimbabwe, Ag: Argentina, Br: Brazil, Ec: Ecuador, Pr: Peru, Au: Australia, PG: Papua New

Guinea. Data from the Annual Bulletin of Statistics (2000).

5740 TEA/Types, Production, and Trade

hectares in 1996. The average yield per hectare has

increased by over 50% during the same period. How-

ever, it is questionable whether any large-scale in-

creases will ensue from now on.

World Trade

Tea Retained in Producing Countries

0032 In 1998, over 57% of the world’s production of tea

was retained in producer countries. In some countries

it was much higher: Over 76% of the Indian and 74%

of the Chinese production is retained for internal

consumption. For India, in particular, the home

market has increased greatly from 499 053 mt

(1988) to 667 565 mt (1998). For a number of other

countries, e.g., Iran, Japan, Malaysia, South Africa,

Taiwan, and the Russian Federation, the majority, if

not all, of their tea produced is consumed internally.

African producer countries generally export the

majority of their production, whereas most Asian

producers do not.

Exports

0033 World exports of tea, both black and green, for the

1995–97 period and for 1998 are reported in Figure 2.

All major exporting countries maintained significant

export volumes for 1998. The FAO projects that net

export availabilities will reach 1.292 million mt in

2005 and predicts that China, India, Indonesia,

Sri Lanka, and Kenya will account for 78% of this

increased volume. Bangladesh, Malawi, Tanzania,

Turkey, and Zimbabwe are also expected to increase

their export capabilities significantly by 2005.

Exports from India, the world’s largest tea-producing

and -consuming country, are expected to recover

from the recent disappointing performance due to

weather, while satisfying growing domestic demand.

0034 The largest and most significant exporter of green

tea is China. Major destinations for green tea include

Morocco, the Russian Federation, Algeria, the USA,

and Afghanistan. India exports small amounts of

green tea to the USA, Afghanistan, and Japan.

China also produces a number of other teas, e.g.,

partially fermented, and the major export destin-

ations for these are Hong Kong and Japan. Taiwan

produces and exports oolong, pouchong, and green

tea, with Japan being the largest importer of these.

The Japanese, in turn, export a small proportion of

their green teas, primarily to the USA.

Imports

0035 Imports for Consumption Figure 3 shows tea im-

ports for consumption of major importing countries

for the 1995–97 period and for 1998. The UK and the

Confederation of Independent States (CIS) countries

– particularly the Russian Federation – were the larg-

est importers of tea for internal consumption. Other

major destinations for tea include Pakistan, the USA,

Egypt, Japan, Iraq, and Morocco. Growth in de-

veloped countries is expected to be largely concen-

trated in the CIS countries, the USA, and, to a lesser

extent, western Europe. Consumption in the UK has

been declining since 1961 when consumption per

head was 4.5 kg, and reached its lowest point of

2.4 kg in 1995. The FAO reports that the apparent

consumption per head has since stabilized and rose

to 2.49 kg in 1996 and 2.58 kg in 1997. This is re-

flected in consecutive increases in net imports for

these years.

0036Reexports of tea A proportion of the tea imported

into the UK is reexported. The largest recipients of

this reexported tea are Canada, Germany, Saudi

Arabia, and France. The Netherlands also reexports

a high proportion of its imports.

Marketing

0037Most of the world’s black tea production is traded

in either auction or forward markets. The former

accounts for the largest proportion of the total tea

traded. In 1997, 84% of the total tea traded was

sold through auctions held in producer countries,

namely: Mombasa (Kenya), Guwahati, (India),

Siliguri (India), Calcutta (India), Cochin (India),

Coimbatore (India), Chittagong (Bangladesh), Col-

ombo (Sri Lanka), Jakarta (Indonesia), and Limbe

(Malawi). The auctions take place weekly through

the growing season.

0038Tea sold through forward contracts is gaining

popularity. A significant advantage of this market

over the auction market is that the participants can

lock on prices they wish to trade in the future. In the

forward market, a buyer and a seller buy/sell an

agreed amount of goods for delivery on an agreed

future date at a predetermined price. Prices in this

market tend to be less transparent than auction prices

(spot or cash markets).

Tea Consumption

0039According to the FAO, black tea consumption will

increase from 1.97 million mt in 1993–95 to 2.67

million Mt by 2005 – an annual growth rate of

2.8%. Statistics collated by the International Tea

Committee indicate that this is an underestimation,

as the total world production for 1998 exceeds

the FAO estimate for 2005. Developing countries

are forecast to account for the largest part of the

TEA/Types, Production, and Trade 5741

prospective increase, with consumption rising from

the 1993–95 average of 1.41 million mt to 1.95 mil-

lion Mt by 2005 – an annual growth rate of 3%.

0040 The FAO reports that black tea consumption in

India will rise rapidly, reaching 832 000 Mt by

2005, annual growth of 3.2% from the 1993–95

average. In other major markets for black teas, such

as Pakistan, the Islamic Republic of Iran, and Egypt,

consumption is projected at 160 000 Mt, 122 000 Mt,

and 90 000 mt by 2005, respectively. The reduction of

import tariffs and declining prices could have a more

pronounced effect on consumption in these countries.

0041 Consumption in the European Community is pro-

jected to increase only slightly in the next decade since

higher purchases by France, Germany, Italy, and the

Netherlands would be largely counterbalanced by the

decline in consumption in the UK that began in 1961.

Consumption in the USA is projected to increase,

though at a relatively slow rate of less than 1%. In

the countries of the former Soviet Union, black tea

consumption is projected to increase from 154 000 mt

in 1993–95 to 250 000 mt in 2005, equivalent to an

annual growth rate of 4.5%.

Trends in World Supply, Demand, and Prices

0042The FAO projections indicate that, by 2005, world

black tea production and consumption could almost

be in balance. Production gains are expected to come

largely from higher yields, while the rise in consump-

tion is from population and income growth. Develop-

ing countries are expected to account for most of

the growth and their share in world consumption is

expected to rise by 2% 2005. However, much

will depend on the economic development of these

countries.

100

125

150

175

200

225

250

275

300

8.5

6.6

9.2

5.6

4.0

0.5

4.0

2.0

4.8

1.15

0.1

5.8

1.8

1.6

3.0

4.0

1.9

0.6

2.3

0.9

0.5 0.5

Ch Ia In Ir Jp My SL Tw Tk Vt Bu Cm Ky Mw Mr Mz Rw Tz Ug Za Zw Ag Br Ec Pr PG Oth

Region

Asia

Africa

South America

Oceania

Other Countries

World

652.1

328.5

52.3

5.8

1.8

1040.4

82.8

0.0

82.6

734.8

328.5

52.3

5.8

1.8

1123.0

Black Tea Green Tea Total

World export of black and green teas

for the year 1995−97

Black Tea

Green Tea

Asia Africa South America Oceania

Other

Countries

100

125

150

175

200

225

250

275

300

Ba Ch Ia In Ir Jp My SL Tw Tk Vt Bu Cm Ky Mw Mr Mz Rw Tz Ug Za Zw Ag Br Ec Pr PG Oth

Region

Asia

Africa

South America

Oceania

Other countries

World

688.8

379.5

63.6

5.3

1.8

1139.0

126.5

0.0

126.5

815.3

379.5

63.6

5.3

1.8

1265.5

Black Tea Green Tea Total

World export of black and green teas

for the year 1998

Asia Africa South America Oceania

Other

Countries

9.7

6.8

5.8

4.9

0.5

5.0

2.0

3.2

1.2 0.2

bbb

5.3

1.8

0.2

3.0

3.5

2.5

0.1

0.6

0.5

2.1

0.4

0.6

Black Tea

Green Tea

fig0002 Figure 2 World export of tea (black and green) for the 1995–97 period and 1998 (1000 Mt).

Black and other teas, but not green teas.

Figures shown are provisional or estimated. Ba: Bangladesh, Ch: China, Ia: India, In: Indonesia, Ir: Iran, Jp: Japan, My: Malaysia,

SL: Sri Lanka, Tw: Taiwan, Tk: Turkey, Vt: Vietnam, Bu: Burundi, Cm: Cameroon, Ky: Kenya, Mw: Malawi, Mr: Mauritius,

Mz: Mozambique, Rw: Rwanda, Tz: Tanzania, Ug: Uganda, Za: Zaire, Zw: Zimbabwe, Ag: Argentina, Br: Brazil, Ec: Ecuador,

Pr: Peru, PG: Papua New Guinea. Data from the Annual Bulletin of Statistics (2000).

5742 TEA/Types, Production, and Trade

0043 The FAO projections suggest an imbalance in the

international market, with a surplus of export avail-

abilities over import requirements, reaching

24 000 Mt by 2005 from an almost balanced market

in 1993–95. This possible imbalance implies that

world market prices would be under downward pres-

sure if there were no additional increase in demand

and/or downward adjustments in production. One of

the ways to narrow the trade deficit and improve

prices is to expand consumption through promotion.

Over the last few years, the IGG on Tea has made

major efforts to create awareness of the health bene-

fits of tea drinking and to work out a generic promo-

tion program that would stimulate consumption of

tea.

0044 The FAO reports that auction prices of black tea

rose significantly during the first quarter of 1998;

however they failed to maintain this vigor during

the remainder of the year. Tea prices were boosted

in 1997 and early 1998 by reports of drought-induced

damage to the crops in Kenya and Indonesia, as well

as strong import demand in the former Soviet Union.

However, following the production recovery in

Kenya, and to a lesser extent in Indonesia, coupled

with a sharp drop in import demand from the Russian

Federation due to deterioration of economic condi-

tions, prices weakened significantly during 1998.

See also: Coffee: Decaffeination; Essential Oils:

Properties and Uses; Phenolic Compounds; Tea:

Chemistry; Processing

Further Reading

Anonymous (1999) Committee on Commodity Problems.

Intergovernmental Group on Tea. Thirteenth Session.

Food and Agriculture Organization of the United

Nations. Ottawa, Canada, 27–29 September 1999.

Anonymous (2000) Annual Bulletin of Statistics. London:

International Tea Committee.

Purseglove JW (1986) Tropical Crops. Dicotyledons.

London: Longman.

Willson KC and Clifford MN (1992) Tea. London:

Chapman & Hall.

Chemistry

P O Owuor, Tea Research Foundation of Kenya,

Kericho, Kenya

Tea

0001Tea beverages are processed from the young tender

shoots of Camellia sinensis (L) O. Kuntze. The plant

biosynthesizes several chemicals during growth.

Table 1 summarizes the approximate chemical com-

position of dry tea leaves. The polyphenols, domin-

ated by catechins (or flavan-3-ols) constitute up to

32% of the dry weight of young tender shoots. The

tender tea plant shoots also contain both saturated

and unsaturated fatty acids, either as glycosides or as

100

125

150

175

200

225

250

275

300

9.4

1.3 1.4

2.8

7.1

5.2 5.5

2.6

CIS G Po Fr Ir OE Ca US WI Ch OL Au Du Su Af Ir Iq Jp Jo Pk Sy OAs Eg Lb Mo SA Su Tu OAf

Oth

Region

Europe

North America/West Indies

Latin America

Oceania

Asia

Africa

430.0

100.3

15.9

16.6

363.8

203.7

436.7

115.1

16.7

409.9

215.1

866.7

215.4

32.6

33.3

773.7

418.8

Other Countries 21.8 22.2 44.0

World 1090.6 1215.7 2306.3

1995-97 1998 Total

Europe North America/

West Indies

Tea imports for consumption for selected

countries for the year 1995−97 and 1998

Africa Other

countries

Latin

America

Oceania Asia

Yr. 1995−97 Yr. 1998

fig0003 Figure 3 Tea imports for consumption for selected countries for the 1995–97 period and 1998 (1000 Mt) (imports adjusted for re-

exports).

Figures shown are provisional or estimated. UK: United Kingdom, CIS: Commonwealth of independent states (former

Union of Soviet Socialist Republics), G: Germany, Po: Poland, Fr: France, Ir: Ireland, OE: Other European countries, Ca: Canada,

US: United States of America, WI: West Indies, Ch: Chile, OL: Other Latin American countries, Au: Australia, Du: Dubai, Su: Saudi

Arabia, Af: Afghanistan, Ir: Iran, Iq: Iraq, Jp: Japan, Jo: Jordan, Pk: Pakistan, Sy: Syria, OAs: Other Asian countries, Eg: Egypt, Lb: Libya,

Mo: Morrocco, SA: South Africa, Su: Sudan, Tu: Tunisia, OAf: Other African countries. Data from the Annual Bulletin of Statistics (2000).

TEA/Chemistry 5743

free acids. There are also methlyxanthines (mainly

caffeine), amino acids and proteins, terpenes, and

terpene glycosides, and many endogenous primary

volatile flavor compounds. Although the biosynthetic

pathways of these compounds are interesting, only

the chemical and biochemical processes (after the

young tender shoots have been plucked to make

various kinds of tea beverages) are discussed here.

0002 Of the many tea beverages, the most extensive

chemical transformations occur during black tea pro-

cessing. The article shall therefore reflect the chemis-

try of tea as represented by black tea manufacture,

although, these chemical reactions partially occur

to different degrees in the processing of other tea

beverages.

Polyphenols

0003 Polyphenols play a key role in the chemistry of the

formation of the nonvolatile components of black

tea. Although attempts to understand the chemistry

of the formation of the nonvolatile black tea compon-

ents started over half a century ago, to date, the

chemistry is only partially understood. The young

tender shoots of the tea plant used to process tea

beverages contain high amounts of polyphenols,

comprising flavanols (catechins), flavanol glycosides,

leucoanthocyanins, and phenolic acids, etc.

0004The dominant polyphenols in green leaf are flavanol

(Figure 1) comprising (þ)-catechin (C), (þ)-gallocate-

chin (GC), ()-epicatechin (EC), ()-epigallocatechin

(EGC) and ()-epigallocatechin gallate (EGCG).

These compounds dominate the chemistry of non-

volatile compounds in tea. Several factors, including

climate, genetic make-up, age of shoots and agro-

nomic practices, cause variations in the total amounts

and ratio of these compounds in young tea shoots.

Although, recently, ()-epicatechin-3,5-digallate and

3-methylgallates of ()-epicatechin and epigallo-

catechin have been isolated in green tea leaves, their

chemistry with respect to tea processing remains un-

known. (þ)-Catechin-3-gallate (CG) and (þ)-gallo-

catechin-3-gallate (GCG) have also been isolated in

manufactured teas, but not from fresh leaves. They

are likely products of epimerization or racemization

caused by firing (drying).

0005The other important component in the chemistry of

nonvolatile components of tea is polyphenol oxidase.

This is an o-dihidroxyphenolic oxygen reductase

enzyme leading to the production of o-quinones.

The enzyme is abundant in young tender shoots of

green tea leaves, especially those cultivars suitable for

making black teas.

0006The most noticeable chemical transformations/

changes occur during the fermentation phase of black

tea processing. Although this stage is called fermenta-

tion, in the true sense, the reactions that occur are

those of oxidation. Following cell matrix destruction

brought about by maceration, the catechins (flava-

nols) and other polyphenols undergo polyphenol

oxidase initiated reactions, forming brown-colored

products. The 1,2-dihydoxyphenols are oxidized to

the quinones in the presence of oxygen, reacting fur-

ther to form various brownish compounds. A simple

catechin and a gallocatechin, for example, undergo

oxidative reactions, which involve a loss of carbon

dioxide to form a benzotropolone ring system. The

compound formed is known as ’theaflavin.’ Figure 2

outlines the formation of theaflavin.

0007From various combinations of the flavanols, it is

possible to produce several theaflavins, as shown in

Table 2. However, the dominant theaflavins found in

black tea are theaflavin, theaflavin-3-gallate, theafla-

vin-3

-gallate and theaflavin-3,3

-digallate. The pro-

portions of these four theaflavins in black tea vary

with processing conditions and the composition of

the individual precursor flavanols in green leaf.

0008Traces of epitheaflavic acid, theaflavin acid, and

epitheaflavic acid-3

-gallate have also been found in

black tea. Normally, there is very little gallic acid in

green leaf. However, during fermentation, its levels

tbl0001 Table 1 Approximate chemical composition of young shoots of

Camellia sinensis var. Assamica

Type Components Dry

weight (%)

Water-soluble Phenolic compounds 40

Flavanols 18–30

Epigallocatechin

gallate

9–13

Epigallocatechin 3–6

Epicatechin gallate 3–6

Epicatechin 1–3

Gallocatechin 1–2

Catechin 1–2

Flavonol glycosides 3–4

Proanthocyanidins 2–3

Phenolic acids 4

Caffeine 3–4

Amino acids 4

Theanine 2

Others 2

Carbohydrates 4

Organic acids 0/5

Partially water-soluble Starch 2–5

Other polysaccharides 12

Proteins 15

Ash 5

Water-insoluble Cellulose 7

Lignin 6

Lipids 4–9

Pigments 0.5

Volatiles 0.01–0.02

5744 TEA/Chemistry

increase, probably from the hydrolysis of galloyl

esters from the catechins or gallated theaflavins. Al-

though the rate of oxidation of gallic acid to the

quinone acid is low, the presence of theaflavic acids

is suspected to originate from gallic acid. Additional

isomers of the theaflavins can also arise from

racemization and epimerization of the flavanols.

However, since racemization and/or epimerization of

flavanols occur mainly during firing, very few isomers

of theaflavins are normally found in black tea.

0009Theaflavins account for 0.3–1.8% dry weight of

black tea and 1–6% of total solids in tea. They are

tbl0002 Table 2 Synthesis of theaflavins from pairs of flavanols

Parent flavanols Theaflavin

Dihydroxy Trihydoxy

()-Epicatechin ()-Epigallocatechin Theaflavin

()-Epicatechin ()-Epigallocatechin gallate Theaflavin-3-gallate

()-Epicatechin gallate ()-Epigallocatechin Theaflavin-3

-gallate

()-Epicatechin gallate ()-Epigallocatechin gallate Theaflavin-3,3

-digallate

()-Epicatechin (þ)-Gallocatechin Isotheaflavin

(þ)-Catechin (þ)-Gallocatechin Neotheaflavin

()-Epicatechin (þ)-Gallic acid Epitheaflavic acid

()-Epicatechin gallate (þ)-Gallic acid Epitheaflavic acid-3

-gallate

(þ)-Catechin (þ)-Gallic acid Theaflavic acid

(þ)-Catechin gallate (þ)-Gallic acid Theaflavic acid-3

-gallate

OHO

i (−)-Epicatechin;

ii (−)-Epicatechin-3-gallate;

iii (−)-Epicatechin-3,5-digallate;

= R

= H

= 3,4,5-trihydroxy-benzoyl,

= R

= 3,4,5-trihydroxy-benzoyl

vii (+)-Catechin;

R = H

viii (+)-Catechin-3-gallate;

R = 3,4,5-trihydroxy-benzoyl

ix (+)-Gallocatechin;

R = H

x (+)-Gallocatechin-3-gallate;

R = 3,4,5-trihydroxy-benzoyl

iv (−)-Epigallocatechin;

v (−)-Epigallocatechin-3-gallate;

vi (−)-Epigallocatechin-3,5-digallate;

R = R

= H

trihydroxybenzoyl, R

= H

= 3,4,5-

= R

= 3,4,5-

trihydroxybenzoyl

fig0001 Figure 1 Structures of dominant flavanols in young tender shoots of tea plants.

TEA/Chemistry 5745

bright red pigments that give the tea liquor its char-

acteristic ’brightness’ and ’briskness’. The contribu-

tions of the individual theaflavins to quality differ,

with the gallated theaflavins being more astringent.

0010 The other set of brownish compounds formed

during black tea processing are called ’thearubigins.’

Despite over 60 years’ research, a full chemical char-

acterization of thearubigins has yet to be achieved.

Indeed, even their contribution to tea quality is not

fully understood. The thearubigins are a group of

compounds, of which some fractions have a large

molecular weight and are nondialyzable compounds.

The mixture of groups of compounds normally called

thearubigins has been identified to have fractions of

polysaccharides, proteins, nucleic acid anthocyani-

dins, cyanidin, and delphinidin. Indeed, the thearubi-

gin structure could be a polymeric proanthocyanidin.

The thearubigins are thought to be polymeric

products of the various polyphenols. Indeed, a 4–8

interflavanoid bonding has been considered possible

after oxidation of catechin. Over 40 peaks represent-

ing pigmented components have been separated by

HPLC from black tea liquor, in the range of expected

thearubigins. With prolonged fermentation, theafla-

vins undergo oxidative degradation. Thus, apart from

thearubigins being formed directly from the cate-

chins, and breakdown of thearubigins, theaflavin

intermediates may also be involved in the coupled

oxidation leading to more thearubigins. Thearubigins

may not be a group of compounds with a common

basic structure. They may be colored compounds

resulting from catechin oxidation, catechin coupling

without benzotropolone ring formation and catechin–

anthocyanidin interactions. Other high-molecular-

weight compounds formed by the interactions

between flavanol quinones with other macromol-

ecules such as proteins, carbohydrates, and nucleic

acids are also classified as thearubigins.

0011The proposed strategy for the formation of thea-

flavins and thearubigins from flavanols is summari-

zed in Figure 3. The formation of one theaflavin

requires one molecule of a simple catechin and a

gallocatechin. Tea shoots normally have higher

amounts of the gallocatechins than of the simple

catechins. This imbalance in the ratio affects the abil-

ity of particular leaves to make theaflavins, and may

direct most gallocatechins to make thearubigins. The

redox potentials of the individual flavanols to quin-

ones also affect the amounts of the particular quinone

available for reaction to produce theaflavin. The

availability of a high polyphenol oxidase activity

and oxygen are therefore critical in the direction of

theaflavins to thearubigins formed under ideal condi-

tions. However, even under ideal conditions, after

some time, the formed theaflavins start degrading

to thearubigins. Resultant thearubigins also degrade

further or polymerize to other thearubigins.

0012Oxygen is required in three key steps: the oxidation

of catechins to quinone, benzotropolone ring forma-

tion, and oxidative degradation of theaflavins. The

first two are necessary for theaflavin formation. For

the formation of high amounts of theaflavins, excess

HOOC

(O)

fig0002 Figure 2 Mechanism of theaflavin formation. From Takino Y, Imagawa H, Horikawa H, and Tanaka A (1964) Studies on the

mechanism of oxidation of tea leaf catechins – formation of a reddish/orange pigment and its spectral relationship to some

benzotropolone derivatives. Agricultural Biology and Chemistry 28: 64–71, with permission.

5746 TEA/Chemistry

oxygen should therefore be available. The flavanols

have a high affinity for oxygen. When oxygen is

limiting, the benzotropolone ring system formation

becomes inhibited, and fewer theaflavins are formed.

However, during the theaflavin formation, there is

also competitive degradation of theaflavins. With

excess oxygen and/or when the catechin levels have

been depleted, this reaction can be significant, redu-

cing the amounts of theaflavins, but increasing thea-

rubigins. However, this may not be the only way the

thearubigins are formed. As in any chemical reaction

system, the reaction temperature is critical. Fermen-

tation of temperatures between 15 and 30



Cis

beneficial to theaflavin formation. However, a higher

temperature fermentation facilitates thearubigin

formation at the expense of theaflavins.

0013 Firing terminates the chemical reactions associated

with the formation of the nonvolatile black tea com-

ponents. Firing heat denatures polyphenol oxidase,

reduces the moisture content to a product that can

be stored, and enhances reactions responsible for

black tea aroma. Firing black teas at temperatures

above 100



C increase the blackness, which may be

due to pyrolytic reactions.

0014 Thearubigins comprise 9–19% black tea dry weight

and 30–60% soluble solids in black tea. They contrib-

ute to the ’liquor color’ and ’thickness’ or ’body.’

Methyl Xanthines

0015 The caffeine is the major purine alkaloid in tea leaves,

but theobromine and theophylline are also found,

albeit in low quantities. Dry fresh tea shoots contain

about 3–4% caffeine. After the shoots are plucked,

the levels of caffeine increase slightly during

withering. However, the levels do not change during

fermentation and may decrease slightly during firing.

A good ratio of caffeine and theaflavins in black tea

imparts a brisk character to the liquors. High levels of

caffeine in tea lead to the so-called ’creaming down’

in the liquors, an indication of high quality.

Other Tea Components

0016Many aroma compounds have been identified in vari-

ous teas. Their biogenetic pathways in green leaf have

been worked out. However, here, only the chemistry

of formation of volatile flavor compounds during tea

processing shall be highlighted. The aroma com-

pounds in tea can be classified broadly into primary

or secondary products. The primary products are

biosynthesized by the plant, whilst the secondary

products are produced during tea manufacture via

enzymatic, redox, or pyrolytic reactions of carotenes,

amino acids, unsaturated fatty acids plus other lipids,

and terpene glycosides.

0017Some aroma compounds constitute both primary

and secondary products. The primary compounds

that have been identified in fresh green teas include

Z-2-penten-1-ol, n-hexanol, Z-3-hexen-1-ol, E-2-

hexen-1-ol, linalool plus its oxides, nerol, geraniol,

benzyl alcohol, 2-phenylethanol, and nerolidol. Their

quantities change after plucking and during tea pro-

cessing. In the course of manufacture, the concentra-

tions of some of the alcohols increase, possibly due to

hydrolysis of their glycosides, whereas for others,

there is a decrease due to oxidative reactions and

glycosidation.

Amino Acids

0018After a tea leaf has been plucked from the plant, the

concentration of amino acids in the leaf increases as

the proteins in the fresh green tea leaf break down in a

process catalyzed by peptidase. The dominant amino

acid in tea is theanine (5-N-ethylglutamine), account-

ing for 2% dry weight or 50% of total amino acids in

tea. In green tea, theanine is associated with a ’brothy’

taste. High levels improve the green tea quality. In

black tea, however, high levels reduce the quality.

This amino acid does not undergo the chemical trans-

formations that the a-amino acids undergo to make

volatile compounds. In black tea processing, the

amino acid levels, decrease during fermentation,

and this is accompanied by the production of

aldehydes, as outlined in Figure 4. Valine, leucine,

isoleucine, and phenylalanine are converted to 2-

methylpropanal, 2-methylbutanal, pentanal, and

phenyl acetaldehyde, respectively. These reactions

EGCQ

EGC

ECQ

fig0003 Figure 3 The formation of theaflavin and thearubigin from the

catechin and possible role played by the simple catechins in

coupled oxidations. EC, epicatechin; EGC, epigallocatechin;

ECQ, epicatechin quinones; EGCQ, epigallocatechin quinone;

TF, theaflavin; TR, thearubigin.

TEA/Chemistry 5747