2009_Book_FoodChemistry

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 reducing
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 factor.
The fresher the tea leaf used in manufacture,
the better the tea produced. Since oxidative processes
catalyzed by the leaf enzymes are undesirable,
the enzymes are inactivated at an early stage
and their reactions are replaced by thermochemical
processes. In contrast to black tea manufacture,
withering and fermentation stages are omitted
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 content
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 tasting
beverage. In China and Japan it is often aromatized
by flowers of orange, rose or jasmin. Yellow
tea and red tea (Oolong) occupy an intermediate
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 fermentation.
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 flavor
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 similar
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 preferred
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 preferentially
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, steaming
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 Darjeeling
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 regional
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-