Orthodox Black Tea Manufacturing Process

Tea Manufacturing 

Tea is a product with different colour, taste, smell as well as different shapes in visual appearance based on its type or variety, but its processing methods are almost similar with minor variations. However, the quality and the characteristics of the final product basically depend on the contents of the leaf where large number of chemical constituents is present in fresh leaf. The most important group of chemical compounds present in the leaf is polyphenols which undergo series of modifications during black tea manufacturing process to impart the specific colour and flavour of tea brew. In addition, caffeine, amino acids and carbohydrates are also include in the tea leaf, but all the these chemical compounds are stored separately in different specific cells or within the leaf without mix-up to prevent chemical reactions (Roberts, 2008) such as generation of dimeric or polymeric phenolic compounds by polyphenols in the presence of polyphenolic oxidase and oxygen. Tea will deteriorate in no time by fungus attacks, if the moisture and temperature is not carefully controlled during the manufacturing process as well as delivery to the end consumer.  

Tea Plucking

First process step of the tea manufacturing is tea plucking, where tea leaves and flushes including terminal bud with two top young leaves are picked from tea (camellia sinensis) plantations and it was transported to manufacturing facilities in ventilated trucks under loosely packed conditions (Sen et al., 1983). The younger tea leaves contain higher concentrations of relevant chemical constituents which is ideal for the production while coarse leaves contain lower amounts where it is very important to have tender two leaves and the bud for production to manufacture good quality black tea (Roberts, 2008). The plucked tea leaves are subjected to leaf count at the receiving where B – 60 or "Randhalu" method is applied and if the receiving green leaves had more than 75 – 80% of tender shoots with two young leaves and bud will ensure the better quality of the final product (Wijerathne, 2008). The plucking is manual and it was carried out by hand which is a labour intensive process where picking is performed by pulling the flush with a snap of forearm, arm or even by using shoulders while gasping the tea shoot using the thumb and forefinger with middle finger or combination (Sen et al, 1983).

Withering

The first stage of black tea manufacturing is withering, which refers to the changes in green tea leaf from the time it is detached from the plant to the time of maceration (Owuor and Orchard, 1989), while chemical withering involves biochemical changes, which solely depend on time (Das, 2006). Tea leaves were subjected to weighing and scrutinization for quality and moisture on the arrival and taken into withering section of the factory which is normally built on top floors of the tea manufacturing facilities. The leaves were loosely stacked in withering troughs for controlled withering with free flow of air as well as electric fans which can provide heated air flows under controlled conditions where frequent turning and mixing with supervision are mandatory. Normally withering requires 16 to 18 hours depending on the weather condition and the moisture content of the tea leaves (Samaraweera and Mohamed, 2008). Tea leaves are subjected to wilting just after picking from the plant with gradual onset of oxidation where withering is applied to remove excess water from the tea leaves while minimizing the enzymatic oxidation within the leaf (Guang, 2007) which was carried out on the withering troughs in orthodox manufacturing model and it was considered as physical wither. On the other hand, minimum of six hours is required for the desirable chemical changes (Samaraweera and Mohamed, 2008) which have to be minimized or delayed till the leaf is ready for the rest of the processing with exposure to oxygen.  The leaves are subjected to reduce more than quarter of its weight in certain processes which very important to catalyze the breakdown of leaf proteins into free amino acids while increasing the amount of freely available caffeine, that change the flavour of tea (Roberts, 1958). This process was basically considered as chemical wither which starts with the breakdown of larger molecules in to smaller molecules while result in increase of amino acids, flavour compounds, caffeine as well as increase in cell wall permeability for rest of the chemical withering (Roberts, 2008). During this process, approximately 63% moisture is extracted from the leaves, making them soft and pliable for further processing (http://www.tea.lk). Thus it was necessary for the operator to have control of all those important chemical and physical changes, in order to have effective control of quality of the final product (Samaraweera and Mohamed, 2008).

Disruption/Rolling

Most of the Sri Lankan tea factories manufacture orthodox tea because country is renowned for these teas while both producer and the buyer prefer to continue orthodox character of Ceylon teas which was basically carried out using orthodox or rotorvane orthodox rollers (Samaraweera and Mohamed, 2008).  The disruption which is also called as leaf maceration by westerners is carryout to bruise or torn the tea leaves for the promotion of quick oxidation (Guang, 2007) which is very important in tea manufacturing process and it was carried out using manual means or mechanical means based on the requirements. The light bruising is achieved manually while mechanical methods such as kneading, rolling, tearing and crushing are used for more extensive disruption (Varnam et al., 1994) which breakdown the structures inside and outside of the leaf cells allowing to blend oxidative enzymes with various substrates to begin oxidation (Chen and Lin, 2008). The leaf maceration releases some of the leaf juices inside the cells which may aid in oxidation while changing the taste profile of the tea. The rolling process is used to form damp tea leaves into wrinkled strips where tea leaf is wrapped around itself. On the other hand, rolling action further causes some of sap comes out with essential oils and juices inside the leaves to ooze out where taste of the tea is further enhanced (Guang, 2007). In orthodox method, various types of rollers are used to macerate leaf where first roll is mostly used as preconditioning roll with very gentle pressure which promotes distribution of leaf juice on to the surface of twisted particles and it dry up on the surface to enhance blackness of final product. The subsequent rolling program is planned to achieve through breakdown of leaf cells (Roberts, 2008)

The orthodox rolling process is complex and the leaves are rolled by applying mechanical pressure to break up the cells and extract the cell sap at the orthodox roller with approximately around 20 minutes, the macerated  leaves; still damp from the sap are sieved on roll breakers to separate the finer leaves which is called the first dhool. The rolled tea leaf is sieved due to further breaking up of twisted leaves will disappear its twisted-up appearance. Thus prompt separation of fine twisted particles from larger sized bulk is required while controlling of the initiated chemical reactions due to cell breakage is a necessity where roll braking is applied to effectively separate them. The extracted uniformly fine particles are called dhools (Samaraweera and Mohamed, 2008).  These are spread out or stacked on racks immediately for fermentation, while the remaining coarse leaves are rolled for a further 20 minutes under higher pressure. The rolling and roll breaking process is continued up to 3rd dhool or 4th dhool and rest of the coarse leaves which are not pass through the last sieves called the big bulk. As a matter of fact, short rolling time produces larger leaf grades, while longer rolling produce smaller leaf grades. During and after the rolling process, the cell sap runs out and reacts with oxygen, thus triggering the fermentation process while the essential oils responsible for the aroma are released (http://www.tea.lk).

Considering the orthodox black tea fermentation, during the rolling process, cell breakages causes the mixing of enzymes with other chemical compounds while polymerization primarily starts and continues through rolling and roll braking processes. Further, the fermentation is allowed to polymerize on racks or on floor such time as desirable. The completeness of the polymerizing reaction is best judged by the characteristics of the final product. The most important polymerization reaction that is responsible for liquor character is the oxidation of polyphenols by the enzyme polyphenol oxidase and this reaction is highly temperature dependent (Samaraweera and Mohamed, 2008). The optimum temperature range for this reaction is 25 - 30°C (Mohamed and Dahanayake, 2003).

Oxidation/Fermentation

The oxidation of tea represents a series of complex chemical reactions which begins just after the cell maceration in orthodox roller where mixing up of enzymes with other chemical compounds within the cell generates number of reactions (Roberts, 2008). Certain teas require oxidation while some of them need less oxidation due to the specific production methods, however orthodox black tea require 100% oxidation to convert phenolic compounds in to polyphenolic compounds. The oxidation process in tea manufacturing is also referred as fermentation where chlorophyll pigments in the tea leaves are enzymatically broken down while releasing the tannins or transforming into other compounds. The amount of fermentation required for a given tea sample is decided by the process owner based on the finish product quality required and the weather conditions because oxidation is the most important factor in the development of aroma compounds, which gives the resulting tea’s liquor colour, strength and briskness (Roberts, 1958).

Due to the maceration of tea leaves cells and the subcellular compartments disrupted where cytoplasmic polyphenol oxidase (PPO) allows oxidizing the flavan-3-ols in the vacuoles. Thus majority of the monomeric flavan-3-ols are oxidized and polymerized to form thearubigins (TRs) and theaflavins (TFs) (Bailey et al., 1992; Bailey et al., 1993). Nevertheless, the first step of the process is oxidation of polyphenol in the presence of polyphenolic oxidase where polyphenol is converted to very unstable oxidized polyphenol which further react with polyphenols to create more stable polyphenolic compounds using polymerization.

There are two type of polymers produced due to these reactions; the orange red compounds are called Theaflavins (TF) which is generated by dimerization while dark brown compounds or the Thearubigins (TR) are generated due to polymerization of three or more compounds. The percentage formation of TR and TF is related to the fermentation time and the temperature of fermenting dhool where high temperatures will lead to rapid formation of TR groups rather than TF groups which will impart a dull colour to the liquor. Thus control of temperature is of a paramount importance. There are other reactions such as oxidation of carotene and amino acids with oxidized polyphenols which contribute to the flavour of the made tea (Roberts, 2008). Thus optimum temperature range for the reaction is 25 – 30⁰C whereas the completeness of fermentation reaction is best judged by the characteristics of final product (Samaraweera and Mohamed, 2008) which intern find the appropriate price in the tea auction.     

  

Firing

The next step of orthodox tea processing was drying which is carried out to terminate biological reactions by heat denaturation of enzymes while reducing the moisture content to increase the shelf life of orthodox black tea and to enhance the chemical reactions that are responsible for the character and flavour of orthodox black tea (Mauskar, 2007). On the other hand, firing further influence balancing of flavour of the tea, because firing eliminates some of the less desirable low boiling point compound such as volatile constituents are removed while retaining more useful high boiling point compounds (Roberts, 2008). The polyphenolic oxidase enzyme will convert catechins into theaflavins till it reaches the temperature 55⁰C where enzymatic reactions will not be arrested as soon as the fermented tea reached the dryers. Actually fermentation is accelerated at the beginning of the drying where 10 to 15 percent of theaflavin content in the black tea is formed during first 10 minutes of drying (Mauskar, 2007).

In addition, drying process reduces the most of the moisture percentage in the wet dhools which comes out of the dryer mouth reaching after 3% (Samaraweera and Mohamed, 2008). Nevertheless, the colour of the wet dhools changed to black from green due to the transformation of chlorophyll into pheophytin, which imparts the desired black colour of the orthodox black tea while reducing the stringency of black tea due to combination of polyphenols with tea leaf proteins at drying because of elevated temperatures. On the other hand, volatile compounds are reduced due to drying; however, some of the aromatic compounds are formed. The fermented dhools are dried through hot air circulation where it needs around 20 – 30 minute based on the specific manufacturer in conventional drying units while fluid bed dryers are operated around 20 minute with 125⁰C (Mauskar, 2007). 

Grading

The conventionally dried teas are cooled before issued for grading while fluidized bed dryers release tea after cooling which can be directly used for sifting operations.  The sifting is carried out by sorting the leaf particles into different sizes defending on the market demand as well as buyer requirements according to their popular blended brands. The primary objective of the sorting is to enhance the value while imparting the quality. The process of sorting enhances the appearance of the liquor quality while removing the fiber or flakes of coarse leaf particles. Thus sorting is carried out in four stages which are cleaning of fiber, grading, winnowing and colour sorting (Samaraweera and Mohamed, 2008).

Nevertheless, orthodox black tea generally has four scales for quality where whole leaf tea is considered highest quality followed by broken leaves, fannings and dusts. Hence, whole leaf tea is produced without alteration to the tea leaf or with very little alterations where it will end up in finish product with coarser texture while bagged tea has more smooth appearance. However, whole leaf tea is as the most valuable, especially with high content leaf tips. On the contrary, broken leaves are considered as medium grade tea which is basically sold as loose tea while smaller broken grades may be used for tea bags. The next grade fannings are considered as leftover products of larger tea grades which is smaller in size and it is also suitable for the tea bags. Dust is the finest particles of leftover products of all other three types which are also good for tea bags that can be utilized for very fast harsh brews, as the greater surface area of the many particles allows for a complete diffusion of the tea into the water. Fannings and dusts have a darker colour, stronger flavor when brewed but lack sweetness (Embole, 2011).

Bulking

The bulking of made tea is basically carryout to even the latter dhool particles as well as early dhool particles which is very important to eliminate day-to-day variations in the produce and to increase the quantity of a single grade. Most of the orthodox manufacturers use manual methods due to the small quantities manufactured due to large array of grades (Samaraweera and Mohamed, 2008).

Packing

Tea is packed in paper sacks in current manufacturing facilities, however it was earlier packed in plywood box few decades ago and it was the most popular method at that time. Tea may be consumed after many months of preparation where it needs preservation techniques to improve the keeping quality while preserving its desirable characters which will be deteriorate due to the absorption of moisture where packing needs special attention to resistance against moisture absorption (Samaraweera and Mohamed, 2008).  

Tea Brewing

Tea has to be brewed to get the liquor out where about one teaspoon or 2.25 grams of orthodox black tea is used per 180ml of water in 6 ounce cup where it must be steeped in freshly boiled water unlike green teas which turn bitter when higher temperatures were used. On the other hand, whole leaf black teas need to be steeped around 4 to 5 minutes, but broken leaf grades require less brewing times because they have more surface area than whole leaf grades. In addition, Darjeeling tea requires 3 to 4 minutes of steeping to have a better brew (Embole, 2011).

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HISTORY OF TEA

Tea

Tea is an evergreen bush of the genus Camellia, from south-eastern Asia from whose leaves, subject to adequate preparation, an infusion of the same name is prepared. Chinese tea bushes (Camellia sinensis), Assam tea tree (Camellia assamica) and their hybrids – Georgian and Sinhalese tea are the most popular.
Tea is grown not only in Asia but also in many other tropical countries. The main manufacturers of tea are: China, India, Sri Lanka, Kenya and Indonesia.

LandMark events of Tea History 

2737 B.C.E. Tea first discovered in China by the Second Emperor, Shen Nung, known as the Divine Healer.

350 A.C.E. The first description of drinking tea is written in a Chinese dictionary.

400 - 600 The demand for tea rose steadily. Rather than harvest leaves from wild trees, farmers began to develop ways to cultivate tea. Tea was commonly made into roasted cakes, which were then pounded into small pieces and placed in a china pot. After adding boiling water, onion, spices, ginger or orange were introduced to produce many regional variations.

479 Turkish traders bartered for tea on the Mongolian border.

618-906 T'ang Dynasty. Powdered Tea became the fashion of the time. Nobility made it a popular pastime. Caravans carried tea on the Silk Road, trading with India, Turkey and Russia.

780 Poet Lu Yu, wrote the first book of tea, making him a living saint, patronized by the Emperor himself. The book described methods of cultivation and preparation.

805 The Buddhist monk Saicho brought tea seeds to Japan from China.

960-1280 Sung Dynasty. Tea was used widely. Powdered tea had become common.

Beautiful ceramic tea accessories were made during this time. Dark-blue, black and brown glazes, which contrasted with the vivid green of the stirred tea, were favored.

1101-1125 Emperor Hui Tsung wrote about the best ways to make whisked tea. A strong patron of the tea industry, he had tournaments in which members of the court identified different types of tea. Legend has it that he became so obsessed with tea he hardly noticed the Mongols who overthrew his empire. During his reign, teahouses built in natural settings became popular among the Chinese.

1191 Eisai Myoan, the monk who brought Zen Buddhism to Japan, returned from a trip to China with tea seeds, which he planted on the grounds of his temple near Kyoto. Eisai experimented with different ways to brew tea, finally adopting the Chinese whisked tea.

1206 - 1368 Yuan Dynasty. Genghis Khan and Kublai Khan conquered Chinese territories and established a Mongolian dynasty in power for more than a century. Tea became an ordinary drink, never regaining the high status it once enjoyed. Marco Polo was not even introduced to tea when he visited.

1211 In Japan, Eisai wrote a small book on tea, elevating its popularity further.

1368-1644 Ming Dynasty. People again began to enjoy tea. The new method of preparation was steeping whole leaves in water. The resulting pale liquid necessitated a lighter color ceramic than was popular in the past. The white and off white tea-ware produced became the style of the time. The first Yixing pots were made at this time.

1422-1502 The Japanese tea ceremony was created by a Zen priest named Murata Shuko, who had devoted his life to tea. The ceremony is called Cha No Yu, which means "hot water for tea."

1610 The Dutch brought tea to Europe from China, trading dried sage in exchange.

1618 Chinese ambassadors presented Tsar Alexis with a gift of several chests of tea.

1657 Tea was first sold in England at Garway's Coffee House in London.

1661 The Taiwanese began to drink wild tea.

1662 Charles II took Catherine Braganza of Portugal as his wife. They both drank tea, creating a fashion for it. Its popularity among the aristocracy causes alcohol beverages to fall from favor.

1669 Close to 150 pounds of tea were shipped to England.

1689 Traders with three hundred camels traveled 11,000 miles to China and back in order to supply Russia's demand. The trip took sixteen months.

1697 In Taiwan, settlers of Formosa's Nantou county cultivated the first domestic bushes. Dutch ships carried the tea to Persia, the first known export of Taiwanese tea.

1705 The yearly importation of tea to England grew to approximately 800,000 pounds.

1710 Wealthy American Colonists developed a taste for tea.

1773 The Boston Tea Party, protesting high taxes that England levied on tea, began the American Colonies' fight for independence. Under cover of night, colonists dressed as Native Americans boarded East India Company ships in Boston Harbor. They opened chests of tea and dumped their contents into the water. This was repeated in other less known instances up and down the coast.

1776 England sent the first opium to China. Opium addiction in China funded the escalating demand for tea in England. Cash trade for the drug increased until the opium wars began in 1839.

1835 The East India Company established experimental tea plantations in Assam, India.

1834 An Imperial Edict from the Chinese Emperor closed all Chinese ports to foreign vessels until the end of the First Opium War in 1842.

1838 A small amount of Indian tea sent to England was eagerly consumed due to its novelty.

1840 Clipper ships, built in America, sped-up the transportation of tea to America and Europe, livening the pace of trade. Some ships could make the trip from Hong Kong to London in ninety-five days. Races to London became commonplace; smugglers and blockade runners also benefited from the advances in sailing speeds.

1856 Tea was planted in many areas of Darjeeling.

1857 Tea plantations were started in Ceylon, though their tea would not be exported until the 1870's.

1869 A deadly fungus wiped out the coffee crop in Ceylon, shifting preference from coffee to tea.

1869 The Suez Canal opened, making the trip to China shorter and more economical by steamship.

1870 Twining of England began to blend tea for consistency.

1900 Trans-Siberian railroad made transport to Russia cheaper and faster. Java became an important producer as well.

1904 Richard Blechynden created iced tea for the St Louis World Fair.

1908 Thomas Sullivan invented tea bags in New York, sending tea to clients in silk bags which they began to mistakenly steep without opening.

1910 Sumatra, Indonesia grows and exports tea. Soon thereafter, tea is grown in Kenya and other parts of Africa.

1970 The Taiwanese government encouraged its population to drink tea, revitalizing tea culture on the island.

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Tea as a Beverage

Consumption of tea began as a medicine and grew into a beverage in China, in the eighth century (Grigg, 2003). Tea is an evergreen bush of the genus Camellia, from south-eastern Asia, whose leaves were subject to adequate preparation with only the most aromatic, young, top two leaves and the unopened leaf bud. Up to 80,000 hand-plucked shoots were needed to produce one pound of top-grade tea. The production of tea has high labour-intensive steps while processes undergo, which determine the resulting tea’s characteristic colouring, taste and composition where every step has to be monitored to achieve superior quality (http://www.irvingtea.com, 2010). Tea is grown not only in Asia but also in many other tropical countries, but the main exporters are China, India, Sri Lanka, Kenya and Vietnam.

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