Food Chemistry

952 21 Coffee, Tea, Cocoa

India and Sri Lanka tea factories use both rollers
and machines of continuous operation – the
socalled CTC machines (crushing, tearing and
curling). They provide a simultaneous crushing,
grinding, and rolling of the tea leaf, thus reduc-
ing the rolling and fermentation time to 1 to
2 hours. Earl Grey tea is black tea perfumed with
bergamot oil.

21.2.3 Green Tea

In the green tea manufacture, the development of
oxidative processes is regarded as an adverse fac-
tor. The fresher the tea leaf used in manufacture,
the better the tea produced. Since oxidative pro-
cesses catalyzed by the leaf enzymes are undesir-
able, the enzymes are inactivated at an early stage
and their reactions are replaced by thermochem-
ical processes. In contrast to black tea manufac-
ture, withering and fermentation stages are omit-
ted in green tea processing.
There are two methods of manufacturing green
tea: Japanese and Chinese. The Japanese method
involves steaming of the freshly plucked leaf at
95 ◦C, followed by cooling and drying. Then the
leaf undergoes high-temperature rolling at 75 to
80 ◦C. In the Chinese method the fresh leaves are
placed into a roaster which is heated by smokeless
charcoal, and roasted. After rolling and sifting,
firing is the final step in the production of green
tea. During the processing of green tea the con-
tent of tannin, chlorophyll, vitamin C and organic
acids decreases only slightly as a consequence of
enzyme inactivation.
Green tea provides a very light, clear, bitter tast-
ing beverage. In China and Japan it is often arom-
atized by flowers of orange, rose or jasmin. Yel-
low tea and red tea (Oolong) occupy an interme-
diate position between the black and green teas,
yellow tea being closer to green teas, and red tea
to black teas.
Yellow tea production does not include fermen-
tation. Nevertheless, in withering, roasting, and
firing, a portion of tannins undergoes oxidation,
and, therefore, dry yellow tea is darker than green
tea.
Red tea is a partially fermented tea. Its special fla-
vor which is free from the grassy note of green tea
is formed during roasting and higher-temperature
rolling.

21.2.4 Grades of Tea

The numerous grades of tea found in the trade

are defined by origin, climate, age, processing

method, and leaf grade. They can be classified

somewhat arbitrarily:

• According to leaf grade (tea with full, intact
  leaves), such as Flowery Orange Pekoe and
  Orange Pekoe (made from leaf buds and
  the two youngest, hairy, silver leaves with
  yellowish tips); Pekoe (the third leaf); Pekoe
  Souchong (with the coarsest leaves, fourth to
  sixth, on the young twig).


• Broken-tea, with broken or cut leaves simi-
  lar to the above grades, in which the fine
  broken or cut teas with the outermost golden
  leaf tips are distinguished from coarse, broken
  leaves. Broken/cut tea (loose tea) is the pre-
  ferred product in world trade since it provides
  a finer aroma which, because of increased
  surface area, produces larger amounts of the
  beverage.


• Fannings and the fluff from broken/cut leaves,
  freed from stalks or stems, are used preferen-
  tially for manufacturing of tea bags.


• Tea dust, which is not used in Europe.


• Brick tea is also not available on the European
  market. It is made of tea dust by sifting, steam-
  ing and pressing the dust in the presence of
  a binder into a stiff, compact teabrick.

With regard to the origin, teas of especially high

quality are those from the Himalayan region Dar-

jeeling and from the highlands of Sri Lanka.

All over the world there is blending of teas

(e. g., Chinese, Russian, East-Friesen blends,

household blends) to adjust the quality and

flavor of the brewed tea to suit consumer taste,

acceptance or trends and to accommodate re-

gional cultural practices for tea-water ratios. Like

coffee, tea extracts are dried and marketed in the

form of a soluble powder, often called instant tea.

21.2.5 Composition

The chemical composition of tea leaves varies

greatly depending on their origin, age and the

type of processing. Table 21.15 provides data on

the constituents of fresh and fermented tea leaves.

In fermented teas 38–41% of the dry matter is sol-