Exercise

Practical 25 - Processing of plantation Crops

Aim: To conduct practical on processing of tea and coffee.

Theory: Tea is an evergreen woody perennial grown in many Asian countries including China, Japan, Java, Sumatra and India. The plant produces dark green, small shiny leaves with white blossom. In post harvest and manufacturing practices for tea, only mechanical and physical processes are allowed with natural fermentation. It can be manufactured by orthodox, CTC (crush, tear and curl) processing.

Coffee is an important beverage used all over the world. Brazil and Columbia are the largest coffee producers in the world. Coffee is harvested in one of two ways; strip picking (entire crop is harvested at one time either by machine or by hand); selective picking (only the ripe berries are picked individually by hand) during dry season when cherries are bright red, glossy and firm. After picking, the coffee can be prepared either by dry method which produces natural coffee or by wet method which produces washed coffee.


A.) Processing of tea
Tea processing is the method in which the leaves from the tea plant (Camellia sinensis L) are transformed into dried leaves for brewing. Processing steps (Fig 25.1) are as follow:

1. The tea leaves should be harvested at proper time i.e., 2 leaves and bud. Plucking is done at an interval of 8-10 days (high crop period), 12-15 days (low crop period) and about 32-36 leaves can be plucked from single bush.

  • Light plucking: plucking done above mother leaf and is also known as step up plucking. It also helps to increase height of bushes.
  • Hand plucking: When the plucking is done below mother leaf.
  • Level plucking: When plucking is done to the level, irrespective whether mother leaf or fresh leaf.
2. Withering is done to remove excess water from the leaves and by the end of this process, the leaves become pliable enough for rolling.
3. After withering, the leaves are twisted and rolled with rolling machine or by hand to allow breaking of leaf cells. During rolling process, some of leaf juices and oils are released, that gives the tea its distinctive aroma and may aid in oxidation.
4. Processing is done either by CTC processing or orthodox method.
  • The CTC processing is done in machine consists of two cylindrical rollers (61 or 91 cm long and 20 cm in diameter) with stainless steel segment with fine tooth like sharp ridges (3-4 ridges/cm in lengthwise and 50-60 ridges over circumference). The speed of 70:700 and 100:1000 rpm have good effects. The crush, tear and curl (CTC) maceration takes only few minutes.
  • In orthodox processing, the rolling is done normally in 36” or 46” diameter rollers. The roller may be table or jacket moving, normally rotates at 45 rpm speed. Battens help in cutting the leaves in roller. With each turn of roller, the leaf caught between cone and roller jacket subjects to heavy pressure and this result in greater extraction of sap. The withered leaf is then charged into the jacket.
5. Oxidation/fermentation begins once the leaf membranes are broken down enzymatically during the rolling process. It is an important stage in black tea processing. It is a chemical process where oxygen is absorbed and the leaves turn progressively darker. The tannins are released/transformed during this process. During this stage, the most important properties of tea are produced.
6. After oxidation, the leaves are dried evenly and thoroughly without burning by using conventional drying, fluidized bed drying, air drying or baking. Drying of leaves stop the oxidation process. The main objective of drying is to arrest fermentation and to remove moisture and produce good quality tea.
7. Curing/ageing: Curing is not required for all types of teas. Additional aging, secondary-fermentation or baking are curing processes to rich their drinking potential.


25.1


* For different types of teas the extent of oxidation is 5-40% for light oolong tea, 60-70% for darker oolong tea and 100% for black tea. During fermentation, low temperature (200C) and high humidity (95%) are desirable.
Characteristics of tea

Appearance and colour

Dried tea should be black.

Strength

Proper twist, green in appearance, All desired characteristics should be there.

Briskness

Tickling sensation in salivery glands.

Flavour

Tea produced in high elevations is having good flavour.

Infusion

Infused leaves should also be twisted


Grading of tea

Leaf grade

T,G,F,B,O,P

Broken grade

BOP

Dust grade

Special dust



TGFBOP: Tippy Golden, Flowering, Broken, Orange, Pikoe
Flowering Pikoe, Pikoe, Broken Pikoe Orange, Broken Pikoe, Pikoe Dust, Red Dust, Super Fine Dust are the important grades of tea.


B). Processing of Coffee
Coffee processing is the most critical activity in its production. Processing of coffee deals with the conversion of raw coffee fruit into coffee. The quality of the final product depends upon the manner of processing. The methods employed for curing of coffee includes; dry method and wet method to produce unwashed and washed coffee respectively (Fig 25.2). In the dry method, the beans are sun dried to 12-13% moisture. While, in the wet method, the fruit covering the seeds/beans is removed before they are dried. The manufacture of coffee powder involves roasting, grinding, blending and packing.
  1. Raw green coffee does not have any flavour or aroma and has an unpleasant taste. Roasting is a heat treatment which transforms the green beans into aromatic brown nuggets.
  2. Roasted beans are ground to three sizes namely fine, medium and coarse. Coarse ground powder retains aroma and flavour better.
  3. Chicory strength, flavour, aroma and acidity are the chief criteria in judging the quality of coffee.
  4. The packaging of coffee powder is done in various flexible films like polyethylene (PE), cellulose films are suitable for short storage and for long storage high density polyethylene (HDPE) is effective.


25.2


Dry method: The harvested cherries are spread over a concrete, brick or matting surface in suitably at good raked at regular intervals to prevent fermentation. In about 7-10 days the cherries dry to about 11% moisture. The outer shells become dark brown and brittle. The dried cherries are then stored in silos, where beans continue to loose moisture.

Wet method: In wet method, the beans are separated from the skin and pulp using a pulping machine. The beans are stored in a fermentation tank for 12-48 hours, during which time enzymes work to naturally separate the slimy layer (parenchyma) from the parchment like covering (endocarp). When the process is complete, the endocarp has pebbly feel. Coffee processed by the wet method is called wet processed or washed coffee and is found superior in quality as compared to dry processed coffee.


Drying: The endocarp is dried in open sun or in mechanical drier to moisture content of about 11% so that beans can be stored in stable condition. In open sun drying, it takes 7-15 days for drying. The coffee is called as parchment coffee.


Hulling:
In wet processed coffee, hulling is used to remove the hull or dried parchment layer surrounding the beans. In dry processed coffee, hulling refers to removal of husk or whole of dried outer covering of original cherries.


Roasting:
Raw green coffee does not have any flavour or aroma and has an unpleasant taste. Roasting is a heat treatment which transforms the green beans into aromatic brown nuggets. Roasting is done at air temperature of 287.8oC and in this process the beans are kept moving to avoid burning. When the bean temperature reaches 209oC they start turning dark brown and oil (called coffee oil or caffeol or coffee essence) start to emerge. The cooling must be quick in order to preserve the flavour, aroma and keeping quality.


Grinding: The bulk of roasted beans is ground to powder and sold as ground coffee. Roasted beans are ground to three sizes namely fine, medium and coarse. Coarse ground powder retains aroma and flavour better and longer than fine ground powder. Coarse ground powder is more suitable for preparing coffee decoction by percolation. On the other hand, fine ground coffee gives a decoction with high body.

Blending:
Two types of coffee powder are marketed namely pure coffee prepared from coffee seeds only and French coffee. Chicory strength, flavour, aroma and acidity are the chief criteria in judging the quality of coffee.


Packaging: For larger packs of roasted and ground coffee, gas packing under carbon dioxide or under vacuum is effective. Various flexible films like polyethylene (PE), cellulose films etc are used for packing coffee.

Different types of Coffee
  1. Decaffeinated Coffee: The coffee from which caffeine is artificially removed is known as decaffeinated coffee.
  2. Estate Coffee: Production of good quality coffee by highlighting special features of estate can be classified as estate branded coffee.
  3. Monsooned Coffee: These are prepared by the special natural process which possesses a special monsooned flavour, mellow taste and golden look.
  4. High Grown Coffee: The coffee grown at higher elevations more then 1250 m above mean sea level possessing distinct flavour and acidity in cup (tasting). The coffee is of high quality with dense beans.
  5. Mysore Nuggets Extra Bold: The beans are large, uniform blush green in colour with a clean polished appearance. In cup, coffee exhibits full aroma, medium to good body, good acidity and fine flavour with a tint of spice.
  6. Robusta Kaapi Royale: it is made from Robusta Parchment AB from the regions of Mysore, Coorag, Wynad, Shivaroys, Pulneys and Barbabudans. The beans are bold, round with pointed ends and gray to bluish gray in colour. This cup ensures full body, soft, smooth and mellow flavour.

C). Processing of chocolate from cocoa beans
Important steps used for making chocolate from dry cocoa beans include roasting, grinding, refining, conching and tempering.

Roasting:
The dried beans are cleaned, sorted and roasted at 150-160oC for 40-50 minutes. Roasting develops characteristic flavour and colour. It also causes changes in chemical structure of polyphenols producing less astringency compound.


Shelling:
Shelling is done to remove the shells from the beans and grains become regular in size. Shelling is carried and by milling, sifting and winnowing. Shelled beans can be made into fine, smooth chocolate.


Milling:
The roasted, shells and crushed beans are milled to reduce them to even finer particles.


Refining:
Refining converts the milled particles into liquid cocoa mass created as cocoa butter in the beans binds dry particles.

Conching: Conching involves powerful machines called conches to stir the chocolate in a controlled way. It is done in two steps.
  • Dry conching: The chocolate is slowly stirred at above 80oC temperature to remove any residual moisture and improve viscosity.
  • Liquod conching: It is followed immediately after dry conching in the same conch without stopping the machine to affect the texture and creaminess. Little quantity of cocoa butter is also added in the process.
  • Tempering: it is done to transform liquid or semisolid chocolate into a solid. Chocolate is heated to melt the cocoa butter crystals and then cooled carefully. Properly tempered chocolate is smooth and glossy and produces smooth texture in mouth with good flavour and aroma.


Last modified: Friday, 9 March 2012, 5:57 AM