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Traditional Tea Manufacture
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The
tedious, long-drawn-out details of traditional tea manufacture, of the
repeated, meaningless, tossing back and forth and Chinese juggling with
the abused tea leaves, are but too familiar to students of the history
of tea subject: and too disappointing also, when we are moved to ask --
Why all this manipulation? What is the nature of the chemical changes
which take place?
A tea's type is determined by the processing which it undergoes. Leaves
of Camellia sinensis soon begin to wilt and oxidize, if not dried
quickly after picking. The leaves turn progressively darker as their
chlorophyll breaks down and tannins are released. This process,
enzymatic oxidation, is called fermentation in the tea industry,
although it is not a true fermentation. It is not caused by
micro-organisms, and is not an anaerobic process. The next step in
processing is to stop oxidation at a predetermined stage by heating,
which deactivates the enzymes responsible. With black tea, this step is
executed simultaneously with drying.
Without careful moisture and temperature control during manufacture and
packaging, the tea will grow fungi. The fungus causes real fermentation
that will contaminate the tea with toxic and sometimes carcinogenic
substances, as well as off-flavors, rendering the tea unfit for
consumption.
Tea is traditionally classified based on the techniques with which it
is produced and processed.
* White tea: Wilted and unoxidized
* Yellow tea: Unwilted and unoxidized, but allowed
to yellow
* Green tea: Unwilted and unoxidized
* Oolong: Wilted, bruised, and partially oxidized
* Black tea: Wilted, sometimes crushed, and fully
oxidized
* Post-fermented tea: Green tea that has been
allowed to ferment/compost
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 TEA CLASSES |
Teas
may conveniently be divided into the classes which have so long
been recognized by the tea trade and consumers, namely:
- Green teas, the first remove from the
green leaf.
- Oolongs, delicate Black teas, having
properties further developed than
those of Green teas.
- Souchongs, and Congous, both of which
have been called "English
Breakfast" teas by North Americans, because the former teas were the
customary breakfast beverages of the English people before the advent
of Indian teas. In these latter teas, fermentation and firing are
prolonged beyond the treatment of Oolongs. The smoky flavor sometimes
apparent is owing to careless and extreme heating.
In making Green tea, the object seems to be to expel the watery juices
of the leaf and to cure or dry it with the least delay. Hence, the
leaves are not exposed to the sun, but are first dried in the air for a
short time. They are next exposed to artificial heat, which renders
them flaccid and pliable, and prepares them for the third operation of
rolling, which twists the yielding leaf as seen in manufactured tea,
rolls it up into balls, and squeezes out a considerable portion of its
watery juices.
It is a singular fact that in the traditional Chinese methods, they
endeavor to get rid of the exuding juices, while in the traditional
Indian treatment, the manufacturing expert, effort is made to preserve
the sappy juice, and it is continually taken up again by the balls of
leaves. The balls are now broken apart, and the scattered leaves are
submitted to the final drying process by heat, which finishes Green
tea. In this case, it is plainly the heating treatment which develops
the faint flavor and odor of Green tea, for no fermentation is allowed
to begin, unless indeed brief and unobserved action takes place within
the compressed balls.
In traditional making of an Oolong Black tea, which occupies an
intermediate position between Green tea and Black Souchongs and
Congous, the leaves were first exposed to the action of the air for a
considerable time, and in many cases, to the sun also. An incipient
fermentation did take place, although this was denied by some.
There is certainly a chemical change beyond the brief preliminary
drying of traditional Green tea. During this period the leaves (in
China) are stirred and tossed by the hands. The effect, if not the
object, is to expose greater surfaces to the air, and to increase
oxidation. It is during this operation that the leaves first begin to
manifest characteristics of manufactured tea, in the way of a fragrant
tea odor which the green leaf did not possess. The development of sweet
odors in new hay, quite different from those of green grass, and also
the artificial development of flavor in tobacco leaves, may be recalled
in this connection. This prolonged exposure to the air is termed
"withering," and the leaves become soft and flaccid, as they do in the
first artificial heating for Green tea. In withering, the leaves lose
about one quarter of their weight in moisture. The leaves must not be
bruised before the termination of this treatment, or injurious chemical
changes will begin.
The second operation with Black tea is the same rolling into balls,
twisting and squeezing, as in Green tea the sap of the leaf thus
liberated from its cells "is spread all over the surface of the rolled
leaf, where it is in a very favorable position for the oxygen of the
atmosphere to act upon it during the next stage of manufacture, namely,
fermentation." Fermentation is an oxidation process mainly.
For the "fermentation" stage, if that controverted term correctly
designates the process, the rolls are either left undisturbed to heat,
or, as in Indian methods, the rolls are broken up, and the leaves
distributed in drawers, with free access of air. In either case, a
spontaneous heating follows, and chemical action is indicated by a
change of color which reddens and darkens the leaf, and by the
evolution of further pleasant "tea" odors. Some of the tannin is said
to be converted into glucose.
Care must be taken, to arrest fermentation at the proper stage by the
first heating and this heating expels about half of the remaining
moisture of the withered leaves, and probably develops an additional
portion of those volatile oils which give fragrance and taste to
manufactured tea designated by the name of "theol." Too high or too
long continued heating drives off these oils with the watery juices.
They are also wasted by exposure of manufactured tea to the atmosphere.
Heating is sometimes divided into two or three stages.
To procure the extreme type of traditional Black teas, a Souchong or
Congou, the fermentation or oxidation, and the "cooking" process, is
simply carried further, and with higher roasting, some of the volatile
oils and delicate flavors are expelled, or are changed into other
flavors. Judging by diminished effects upon tea drinkers, some of the
volatile theine is also lost.
In both countries, in China and Japan it was the custom to give large
portions of the tea crop which were intended for export to foreign
countries, only a preliminary drying or curing sufficient to preserve
them temporarily. When they arrived at the shipping ports they were
subjected to additional heating and thorough drying.
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