Green tea processing

GREEN TEA PROCESSING

USING INFRARED AND MICROWAVE HEATING

TEA OVERVIEWTea is globally one of the most popular and cheapest beverages with major

production centres in India, China, Kenya, Sri lanka, Turkey & Vietnam. The tea industry is one of the oldest organized industries in india with a

large network of tea producers, retailers, distributors, auctioneers, exporters and packers.

On an average, during the last two decade in the production front, India contributed 28% of the world tea production closely followed by china (25%), Sri lanka (9%) – being green tea producer and Kenya (9%) – ctc producer. 23 % world tea is produced by other countries.

The global productivity during 1991 was 1026 kg/ha which climbed to mere 1100 kg /ha in 2000. In the first decade of 21st century, global tea productivity hovered between 1100-1160 kg/ha. SOURCE: ONICRA (onicra credit rating agency of India)

TEA OVERVIEWOn an average during the last two decade, in the export

front, both kenya and sri lanka lead the world each with 20% of their contribution followed by china (17%), india (14%) and others (25%).

Currently, india produces 23% of total world production and consumes about 21% of total world consumption of tea – nearly 80% of the tea produced is consumed within india.

SOURCE: Basu Majumder A., Bera B. and Rajan, A. 2010. Tea Statistics: Global Scenario.

TEA OVERVIEW

Green tea • Green tea, known as unfermented tea, is a popular beverage in the

world. • The more important of green tea is the flavor and smell.• Chlorophyll content of green tea is around 1.2-1.5 mg/gm of tea

leaves.• Green tea is also recognized as herbal medicine.• Green tea is reputed to be benefit in some areas like cancer, infection,

high cholesterol and impaired immune function.

CHEMISTRTY OF GREEN TEAContents % Dry weight

Proteins 15-20

Amino acids 1-4

Fiber 26

Carbohydrates 7

Lipids 7

Pigments 2

Minerals 5

Phenolic Compounds 30

Oxidized Phenolic Compounds 0

CHLOROPHYLL CONTENT of some leaves

SAMPLE CHLOROPHYLL (a) mg / gm of leaves

CHLOROPHYLL (b) mg / gm of leaves

TOTAL CHLOROPHYLL mg / gm of leaves

Tulsi leaves 1.6486 1.0466 2.7348

Henna (mehndi) leaves _ _ 2.7812

Mint leaves 4.0965 2.0788 6.1743

Curry leaves 5.4534 3.6581 9.1090

Neem leaves 6.0157 5.0268 11.0692

Vasaca leaves 11.86 12.51 20.50

PROCESSING OF GREEN TEAPlucking(harvesting)

Enzyme de-activation /fermentation stopping (by steaming or hot water

pouring)

Fixation

Rolling

Drying

High temperature drying

Low temperature drying (may include flavouring)

PROCESSING OF GREEN TEA

Classification(grading)

Final roasting

Packaging and labeling

Metal detection

Storage / dispatch

GREEN TEA PROCESSING STEPSPlucking : This is the process of harvesting green tea leaves from the tea plants. Young and tender material is collected for a high quality green tea. It is devided into three groups as :o Imperial > bud+ 1 leaf oFine > bud + two leavesoCourse > bud + 3 or more leaves

COURSE PLUCK

FINE PLUCK

IMPERIAL PLUCK

GREEN TEA PROCESSING STEPSDe-enzyming / ezyme de-activation >>The goal is to heat the tea to stop fermentation. If the fermentation is not

completely stopped, the tea liquor will be red. In this process of enzyme de-activation , the tea leaves are steamed so that

enzymatic degradation will be stopped. In some countries the boiling water is also used for de-enzyming.

GREEN TEA PROCESSING STEPS

FIXATION>>Important step in green tea primary processing, critical to obtain high quality.In this way, enzymatic oxidation of tea polyphenols is prevented as well as

unnecessary changes of leave inclusions.While fixing tea leaves will soften for a good rolling, while the moisture content

is reduced and the fragrance fixed.After fixation, the leaves should be spread in thin layers on clean spaces for

natural or forced cooling.


FIXATION PROCESS>>

GREEN TEA PROCESSING STEPSROLLING>>

Rolling is a crucial step for shaping the appearance.

It is often carried out in a rolling machine.

The tea leave quantity, time and pressure, are major technical factors during

rolling.

Tea leaves should look brightly green instead of yellowish and they should

smell fragrant instead of stuffy.

GREEN TEA PROCESSING STEPSROLLING MACHINES / EQUIPMENT>>


DRYING OF GREEN TEA>>>Traditional drying

Conventional drying

Microwave drying

Infrared drying

Hybrid drying processes

DRYING OF GREEN TEATRADITIONAL DRYINGo SUN DRYING This is the same thing that most civilizations have done with their food since before written history: laying down the produce to dry under the sun for preserving to use later. Tea was not any exception. Since prehistory, the chinese has had an especially strong heritage of the use of dried plant materials and tea began as one of the medicinal herbs.o Moisture is reduced upto 4-6 %.

DRYING OF GREEN TEAoSHADE DRYING: In this method of drying the green tea leaves are kept away from direct

contact of sun to avoid loss of overall quality by providing required amount of heat from sun.

DRYING OF GREEN TEAoCONDUCTION DRYING>> In this type of drying the tea leaves are dried by directly roasting on the heated metal of non-metal

surface. The parameters which controls the drying phenomena are temperature,time&amount of green tea

leaves to dried. The final quality of green tea obtained by this drying method has darker color and low sensory

attributes. This is heating of green tea leaves on the metal plate above fire.

DRYING OF GREEN TEARotatory drum dryers are one of the dryers which are used in tea

drying for small scale production of green tea.Controlling parameters for drum dryers are drum rotation

speed,drum internal temperature&processing time.

ROTATING HANDLE FUELS

HOT AIR OUTLETSGROES FOR MIXING TEA LEAVES

DRYING OF GREEN TEACONVECTIONAL DRYING METHODS>>CONVENTIONAL AIR DRYER: In this method of drying the green tea leaves are dried by using heated air with different arrangements of

drying sections. This includes cross flow, concurrent,cocurrent,circulatory and forced circulatory etc. Types of dryer

mechanisms. The controlling parameters in this type of drying are air inlet and exhaust temperature ,drying time, feed rate

. The quality obtained by this method was bit improved from conduction type of drying.

DRYING OF GREEN TREE LEAVESFLUIDIZED BED DRYER FOR DRYING OF GREEN TEA LEAVES>>WHAT IS FLUIDIZATION?? When air is passed through the bed of granular particles of suitable size, shape and specific weight

under suitably controlled conditions the particles can be made to float in the air stream to behave like a fluid, under these conditions it is said to be fluidized and this phenomena is known as fluidization.

In fluidized bed dryers the solids make direct contact with air resulting in higher rate of drying.The improved thermal contact between tea particles and air resulted in uniform drying of each

particles with higher efficiency and with lower cost.This leads to a better quality of dried green tea leaves.The process controlling parameters are minimum fluidization velocity, particle shape size, specific

gravity, air temperature and retention time.In fluidized bed dryer the tea leaves can be fed at feed end and discharged at the dryer end.Till now there are several fluidized bed drying methods have been investigated and designed like the

Sri lanka tri-ccc fluid-bed tea drier etc. .

DRYING OF GREEN TREE LEAVESFLUIDIZED BED DRYER

MICROWAVE DRYING OF GREEN TEAMicrowave drying (MD) is a relatively new drying method. The fundamental mechanism of microwave heating is the agitation of

polar molecules which oscillate under the influence of an oscillating electric and magnetic field.

In the existence of an oscillating field, particles always try to orient themselves with the field.

The activity of particles is restricted by resisting forces (for example electric resistance or interaction), which restrict the activity of particles and generate random movement, thus producing heat.

The key advantage of the microwave heating over conventional heating method is the nature of fast internal heating by microwave energy.

MICROWAVE DRYING OF GREEN TEAMicrowave energy deposition in the dielectric loss mode of heating

can cause spatially uniform heating.

When applying microwave energy to tea, water and other polar molecules of tea are induced for simultaneous high-speed rotation due to microwave irradiation, leading to the surface and interior heating at the same time, and resulting in a large number of water molecules escaped from the tea (Lou, 2002).

However crumple zone may be produced to affect the quality of tea due to high heating rate (Cai, 2005).

MICROWAVE DRYING OF GREEN TEA LEAVES>>oGreen tea manufacture was standardized with respect to the inactivation of

polyphenol oxidase (PPO), rolling, and drying for quality manufacture. Inactivation of PPO by parching, steaming, microwave heating, and oven heating was monitored in tea shoots.

o Fresh shoots of tea are very rich in polyphenols, especially the flavan-3-ol group (catechin and its derivatives), which are present at up to 30% on a dry weight basis.In processing younger tea shoots for green tea manufacture, polyphenol oxidase (PPO) inactivation is necessary to avoid the oxidation of catechins to form theaflavins and thearubigins. These catechins are responsible for the astringency and taste of green teas.

o In steam-inactivated and oven/microwave-dried teas, total phenol and catechin contents were intermediate between parched and sun-dried teas and microwave-inactivated and microwave-dried teas, and their infusions were bright with a umami taste.

MICROWAVE DRYING OF GREEN TEA LEAVESMicrowave energy is transported as an electromagnetic wave in certain

frequency bands in the range between about 0.3 GHz and 300 GHz.When microwaves impinge on a dielectric material, part of the energy is

transmitted, part reflected and part absorbed by the material where it is dissipated as heat.

. Heating is due to `molecular friction' of permanent dipoles within the material as they try to reorient themselves with the oscillating (electrical) field of the incident wave.

MICROWAVE HAS ANunique characteristics, which include the facts that no contact is required between the energy source and the target and that heating is volumetric, rapid and highly specific in nature.

MICROWAVE DRYING OF GREEN TEAThe major food components - water, carbohydrates, lipids, proteins

and salts (minerals) - interact differently with MW. MW interactions with foods depend heavily on salt and moisture

content. Water selectively absorbs the energy.In drier products, the dissolved salts are concentrated (in the

remaining water); if the solids exceed saturation level and precipitate, their ionic conductivities are limited. However, the solids themselves do absorb energy.

MICROWAVE DRYING OF GREEN TEA LEAVES

DRYING OF GREEN TEA LEAVESINFRARED DRYING OF GREEN TEA LEAVES>>WHY INFRARED HEATING OF GREEN TEA LEAVES> Infrared radiant heat transfer is often more efficient than convective

heat transfer. Large amount of controlled heat for heating tea leaves. Uniform heating of the green tea leaves. 15-20 minutes to reduce mc upto 2% (if layer thickness is around 5-

10cm). It takes about 1 minute in heating at 60 degree centigrate.

IR DRYING OF GREEN TEA LEAVESTYPES OF INFRARED RADIATION:

oNEAR INFRARED:: 0.75-1.4 micro meter :: 214-400THz:: 886-1653 meV

o SHORT WAVELENGTH IR:: 1.4-3 micro meter::100-214THz::413-886meV

oMID WAVE INFRARED:: 3-8 micro meter::37-100THz::155-413meV

o LONG WAVE INFRARED:: 8-15 micro meter::20-37THz::83-155meV

o FAR WAVE INFRARED(FIR):: 15-1000 micro meter:: 0.3-20THz :: 1.2-83meV

ADVANTAGES OF IR HEATING OF GREEN TEA LEAVES

• REDUCTION IN DRYING TIME.

• FAST RESPONSE TIMES ALLOW EASY AND RAPID PROCESS CONTROL.

• NO DIRECT CONTACT WITH MATERIAL IS REQUIRED AS IN

CONDUCTION DRYING.

• BETTER COLOR AND FLAVOUR RETENTION THAN CONVENTIONAL

DRYING.

• POSSIBILITY OF SELECTIVE HEATING

INFRARED GREEN TEA DRYING

INFRARED CATALYTIC GAS BURNER

COMPARISSION OF DIFFERENT DRYING TECHNOLOGIES ON THE FINAL QUALITY OF GREEN TEAEFFECT ON REHYDRATION RATIO:

AD VD MD MVD0

0.5

1

1.5

2

2.5

3

3.5

2.542.8 2.88 3.07

Rehydration ratio (g.(g)^-1) Vs different drying methods

different drying methods

rehy

drati

on ra

tio

COMPARISSION OF DRYING RATE

COMPARISION OF NUTRITIONAL COMPONENTS

DRYING METODS

POLYPHENOLS AMINO ACIDS WATER SOLUBLE SUGAR

PROTIEN CAFFINE

AD 24.92 3.17 3.19 1.80 4.25

VD 24.34 3.43 4.07 1.95 4.43

MD 21.58 3.60 2.72 2.08 4.48

MVD 22.0 3.76 2.84 2.54 4.66

COMPARISSION OF PHENOL-AMINO ACID RATIO

AD VD MD MVD0123456789

7.877.09

6 5.86

phenol to amino acid ratio Vs different drying method

Different drying methods

Phen

ol to

am

ino

acid

ratio

COMPARISSION OF SENSORY ATTRIBUTES

DRYING TECHNIQUE SENSORY SCORE (OUT OF 100 )

AD 87.70

VD 89.55

MD 90.97

MVD 93.15

ADVANTAGES OF MODERN DRYING TECHNOLOGIES

1. The MVD drying technology is best in case of overall quality of green tea.2. In some cases the microwave drying is better than conventional air drying.3. But VD is also better than microwave in case of amino acid retention.4. The MD&MVD are very fast drying techniques.5. Better cell structure was maintained by MD with/without vacuum .

DISADVANTAGES>>

1. Very huge capital investment.

2. High operating cost.

3. Problem of leakage with MD & MVD.

REFERENCES1. Cai, Y. 2005. Progress in the drying technology of tea. Fujian Tea, (3): 22–23.2. Lou, L. 2002. Applications of microwave technology in the tea processing.

Fujian Tea, (1): 23–25. 3. Xiao, H. 2006. The equipment development trend of mechanized green tea

processing. China Tea, (3): 40–41.4. Lee, S. C.; Kim, J. H.; Jeong, S. M.; Kim, D. R.; Ha, J. U.; Nam, K. C.; Ahn, D. U.

Effect of far-infrared radiation on the antioxidant activity of rice hulls. J. Agric. Food Chem. 2003, 51, 4400-4403.

5. Gulati, A.; Rawat, R.; Singh, B.; Ravindranath, S. D. Applicationof microwave energy in the manufacture of enhanced-quality green tea. J. Agric. Food Chem. 2003, 51, 4764-4768.

6. LEE, S.C., KIM, S.Y., JEONG, S.M. and PARK, J.H. 2006. Effect of Far-infrared irradiation on catechins and nitrite scavenging activity of green tea. J. Agric. Food. Chem. 54, 399–403.

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Engineering

Green tea processing