Tea Fermentation


• The Chinese sources claim that the first person who drank was the emperor Shen-Nung who lived around 2700 BC.

• tea manufacture  is one of the oldest biotechnologies developed and practiced by mankind.

• Many different types of tea are marketed in the world today.

• Turkey : 160,000 ton black tea production and consumption

China Teas (Camellia sinensis var. sinensis)

• slow-growing  ( grow to a height of 4–6 m if unattended)

• dark green leaves which are smooth with a matt surface

• resistant to cold

• found in  China, Japan, the former Soviet Union, Turkey, Iran, and the northern, higher-altitude growing areas of India.

• to produce delicately flavored tea when grown at high altitudes

• low-yielding, especially at very high altitudes

Assam Teas (Camellia sinensis var. assamica)

• faster-growing  (12–15 m unattended) than the China variety

• larger glossy elliptical leaves

• less resistant to cold than the China type

• much higher-yielding plant than the China type

• produces a less delicately flavored beverage.

Types of tea

1. Green tea ( not fermented )

2. oolong and pouching teas ( partially fermented)

3. black tea ( fully fermented)

• Differences = f (Amount of fermentation)

• most tender portions of tea plants are used to produce best quality teas.

• Immature plant: less woody (i.e Less lignified, more workable in the tea manufacturing process)

Fresh tea shoot tips ( 78 % moisture)

Constituent              % of total dry weight

• protein                                  15    ( including catechol oxidase)

• fiber                                      26

• pigments                               2 ( chlorophyll, caretones )

• lipids                                      7

• caffeine                                4

• polyphenols                         30  ( mostly catechins )

• amino acids                          4

• minerals                                5

• carbohydrate                       7

• volatile compounds            0.1

• approx. 32 % of its ingredients pass into the infusion.

Tea contains:

• Caffeine (teine) / Tannins / Amino acids / Proteins

• Trace elements and minerals: fluoride, potassium, calcium, manganese / Vitamins: niacin, vitamin B1 and B2


WITHERING ( soldurma )

• Shoot tips are picked by hand( plucking)( 78 % moisture) à à Withering (55 % Moisture) 

• Keep temp of respiring tea leaf below 24 C, 6-20 hours, some biochemical changes occur, permeability of plant cell membranes changes.

• In cell cytoplasm carbohydrate, caffeine, amino acid concentration and polyphenol oxidase activity increased.

• ( air temp < 32 C, otherwise leafs break and burns)

• Batch system ( < 35kg tea/m2, turnover within 2 hours)

• Continuous system (< 25 kg tea /m2, thickness < 25-30 cm )

• withering still takes up considerable factory space, and newer methods continue to be developed.

two-stage withering.

•  storing the leaf in a holding tank with minimal moisture loss for about 6 h to achieve chemical wither  then spread on withering troughs, or a moving belt witherer, and the moisture is rapidly reduced by the use of warm air.

• drum withering, tunnel withering, Tocklai continuous withering machines, Russian withering machines, and automatic continuous operating installations.

• in the unorthodox methods of producing plain black tea, physical withering is not essential to produce high-quality black tea. Some factories are therefore now processing plain black tea after achieving chemical withering but without physical withering.

TISSUE MACERATION (ROLLING) (kıvırma)(250-300 kg / 45 Minutes) (breaking, squizing, bending).

• Maceration ruptures the leaf cell structure, exposing the chemical constituents of the cells, mainly polyphenols, oxidative and degradative enzymes, lipids, amino acids, etc., to oxygen.

• Most importantly, catechins come into contact with the polyphenol oxidase enzyme, initiating ‘tea oxidation,’ which is erroneously referred to as ‘fermentation.’  The most common methods:

• The orthodox rolling, crush, tear, and curl (CTC), and Laurie tea processor (LTP) methods.

• The method used has a significant effect on the resultant black tea.

• orthodox rollers: less cell matrix destruction, leads to fewer oxidative reactions,  slow fermentation  (Tea is plucked by hand, the top two leaves and the bud is plucked in a fine plucking. select the newest growth of the tea plant )

• CTC (Tea is harvested by machine. CTC methods cut off a foot or more of the tea plant. The stems are processed along with the leaf by the CTC method. )

• LTP maceration methods : greater cell matrix destruction, more extensive oxidation, less aromatic tea, higher plain tea quality parameters(  more intensive color than orthodox)

•  LTP requires a softer physical wither than CTC processing.

• The action also aerates the mass of tissues and causes some temp increase.


FERMENTATION (1.5 to 3 hours, RH: 90-95 % , 24-26 C, tunnel-continuous system)

• Tea fermentation is the oxidation of tea catechins mediated by the tea catechol oxidase enzyme and all the secondary reactions associated with this primary oxidation.

• All the reactants except oxygen are endogenous to the tissues of the tea shoot tips..

• Under ideal conditions, the primary reactants of tea fermentation remain spatially separated (i.e. the catechin in vacuoles of tanniferous cells, and the catechol oxidase enzyme within the cytoplasm of intact cells in the tissues) until tissue maceration step.

• Withering destroys the semi permeable properties of the cellular membranes allowing the cell contents to become mixed under the action of tissue maceration process. Once the catechins and catechol oxidase are brought together in the presence of oxygen, tea fermentation begins.

Tea catechin     à     orthoquinones      à        theaflavins (bright red  color fair solubility acts as oxidizing

oxidized may condense  agent to oxidize others) with one another                                                                                                               

Gallic acid        à                  à              epithea flavic acid (Bright red excellent solubility) oxidized condensed with oxidized catechin

• Black tea aroma: hundreds of volatile compounds.

• Some of these compounds are present in fresh green tea shoot tips but the characteristic aroma of black tea is formed during fermentation.

• The tea fermentation process is normally carried out at ambient temp and the process takes from one to five hours to complete.

• During this time the tea plant material changes color from green to coppery red , and the aroma changes from grassy to sweet and flavory.

DRYING Firing (Drying)

• to terminate fermentation and to dry tea for storage and transport.

• the temperature rises, some reactions are accelerated until the rise is adequate to denature the enzymes or moisture has been adequately removed to prevent reactions occurring, but a lot of changes occur to give black tea its character. 

• The color changes as a result of the transformation of chlorophyls to pheophytins and pheophorbides.

• Some caffeine is lost while the amount of volatile flavor compounds is reduced.

• The volatile flavor compounds that result from various pyrolytic reactions are formed during firing


• Mechanical sieving —–smallest fraction ( best) —-coarse fraction

• Screen numbers 8-10-12-20-32 ( # of openings in one inch square)

• 1st grade : 20/30 (completely fermented, best quality)

• 2nd grade: 12/20 (very little unfermented tea ) referred as  –imalat kırığı

• 3rd grade : 10/12 ( little unfermented tea) tea collected under 30 ( pan—-referred as toz çay) tea collected 8/10 mechanically rebroken -referred as kırık çay) this tea is sieved again to obtain:

• 4th grade : 20/30

• 5th grade:  12/20

• 6th grade   10/20

• 7th grade Dust ( pan portion)

Volume of tea

• One of the important quality criteria for tea is its density. Usually volume ( cc) of 100 gram tea is measured. Small volume ( in turn higher density indicates higher quality)

• Tea from fresh ( young ) tea shoots : density is high

• Tea from old leafs : density is low ( Because its cellulose content is high)

• Few weeks of maturation ( then can be stored one year)

Standards related with quality of tea:

 Grades                   1 2          3          4           5           6            7

stems % max                          12          3          4            5           5            4

unfermented piece max      2        2          3          4            8           8            4 

volume cc/ 100gr              360    500 650      360        480 580         280

• Moisture contents in excess of 6.5% are extremely detrimental as this encourages rapid fungal and bacterial growth.

• Conversely, teas that come out of the drier with moisture contents of 2.5%, or less, generally have a ‘smoky’ taint, if firing has been carried out using a conventional dryer.

Quality based on tea shoots (sürgün

                             1st tea shoots         2nd tea shoots     3rd tea shoot

volume cc/100grams

• 1st grade              310                         320                        320

• 2nd grade              420                         440                        440

• 3rd grade               520                         540                        540

• tea must not be stored in close proximity to any commodity with a strong smell due to its remarkable ability to pick up odors.


1 2       3 Total       4        5         6          7        Total       dry tea yield 

• 1st tea shoots      3       20 10         33          8 47        8           4          67            21

• 2nd tea shoots     3 20      9          32 8        48        8           4          68           20.5

• 3rd tea shoots      3       20 8          31         8         49 8          4           69           20 

Green tea

• attempts are made to insure that there is no oxidation, especially that of the catechins.

• The process therefore starts with steaming or roasting to deactivate polyphenol oxidase activity.

• The green teas are made from tea plant varieties with a lower catechin content than those for black tea, but this level is sufficient to create astringency.

• The volatile components of green tea are basically those of the primary products.

• Withering is not mandatory in green tea manufacture.

• In China, green tea manufacture begins by roasting the leaf in a hot iron pan for a few minutes, followed by hand rolling on a table.

• The leaf is then subjected to two or more further roastings and rollings.

• In Japan, the leaf is steamed for 15–20 s in a revolving cylinder provided with an agitator.

• The steamed material is cooled by a fan or by air on a belt conveyor and then subjected to primary heating and rolling.

• The leaf may undergo further heating and drying before passing through secondary (final) rollers.

• The green tea is then dried to a moisture content of about 3–4%.

 Oolong tea ( 50 % fermented)

• Manufactured in a similar manner to green tea, but with the following variations.

• The fresh leaf is withered at room temperature for approximately 16 h, or at 40 °C for 2 h followed by another 4 h at room temperature.   

• In both cases, during the last 4 h, the leaf is rolled by hand for a period of 30 min every hour.

• This is followed by roasting (parching or pan frying) at about 160 °C for about 20 min.

• The tea is rolled further and then fired.

Pouchong tea (30 % fermented )

• process is slightly different than for oolong.

• The leaf is withered in the sun (solar withering) for 15 min, during which time it is turned over once.

• This is followed by indoor withering for 3 h, during which time the leaf is turned over three times.

• The leaf is then pan-fried at 160 °C for 20 min, rolled by hand for about 20 min, and dried at 80–85 °C for 40 min.

• Low-grade pouchong tea is often scented by blending with jasmine flowers to enhance the flavor (jasmine tea).

Earl Grey tea

• This popular black tea was named for Charles Grey, the second earl in his line, who was also prime minister to King William IV in the early 19th century.

• An amalgamation of Indian and Sri Lankan teas, Earl Grey gets its elusive flavor from oil of bergamot ( bergamot orange)

• A small tree (Citrus aurantium subsp. bergamia) commercially grown chiefly in southern Italy for its sour citrus fruits, the rinds of which yield an aromatic oil. ( a cross between the pear lemon and the Seville orange or grapefruit )

• The Earl is said to have been given the recipe by a Chinese mandarin with whom he was friends

Instant tea

• Tea extracts may be concentrated and spray dried directly to produce products that require hot water for redissolving (due to insoluble complexes that form at room temperature between the caffeine and polyphenolic compounds that are present in all tea extracts.)

• Cold water soluble instant tea products are manufactured by chilling the tea extract, separating the insoluble caffeine/tea polyphenol complex., that forms , and treating this precipitate in such a way as to render it soluble.

• An alkaline-air mediated oxidation of tea polyphenols is the most commonly used process, although  an enzymatic treatment using the enzyme tannase has been also used.( for ice tea production)  

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