Processing of Horticultural Crops

Introduction

Introduction
Plantation crops are high value industrial crops grown in the tropics having great economic importance. They have great potential for utilization of waste land like rainfed dry land, hilly, arid and coastal areas to provide nutritional security, earn foreign exchange and to ensure livelihood security. The major plantation crops grown in India are tea (Camellia sinensis L), coffee (Coffea arabica L.), rubber (Hevea brasiliensis), coconut (Cocos nucifera), arecanut (Areca catechu L.), oilpalm (Elaeis guinensis), cashewnut (Anacardium occidentale L.) and cocoa (Theobroma cacao L.). India is the leading producer of most of these plantation crops. Among all fruit crops, the processing plays an important role in plantation crops as they are generally consumed only after processing. Coconut, arecanut, cashewnut, black pepper and cardamom are known as small holder plantations whereas, crops like rubber, tea and coffee are known as estate crops or conventional plantation crop.

A. TEA (Camellia sinensis L)
Tea is an evergreen woody perennial grown in many Asian countries including China, Japan, Java, Sumatra and India. Tea belongs to family Camelliaceae. 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 followed with natural fermentation. It can be manufactured by orthodox, CTC (crush, tear and curl) processing.
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 broadly involves picking, withering, rolling, oxidation/fermentation, drying and curing/ageing. The steps involved are as follow:

1. Picking: Tea leaves and flushes, which include a terminal bud and two young leaves, are plucked from Camellia sinensis bushes twice a year during early spring and early summer or late spring. Generally hand picking is preferred for picking of tea leaves. Hand picking is done by pulling flush with a snap of wrist and does not involve twisting or pinching of flush, as twisting generally reduce the quality of leaves. Machine picking results in more broken leaves and is not suitable on mountain slopes where tea is grown.

2. Withering: Withering is used to remove excess water from the leaves and sometimes loose more than a quarter of their weight. Newly picked leaves are thinly spread in the sun or left in a cool breezy room to pull moisture out from the leaves. Heated air is sometimes forced over the leaves if the climate is not suitable. By the end of this process, the leaves become pliable enough for rolling. In order to quicken the oxidation process, the leaves may be bruised by tumbling in baskets or rolled-over by heavy wheels. The main purpose of this process is the partial expulsion of moisture and thus saving fuel consumed in drying operation and allows a very light oxidation.

3. Rolling: From the withering racks, the leaves are twisted and rolled 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. The leaves can be rolled with rolling machine or by hand.

a) CTC processing: The CTC (crush, tear, curl) machine consists of two cylindrical rollers (61 or 91 cm long and 20 cm in diameter) having stainless steel segment having fine tooth like sharp ridges (3-4 ridges/cm in lengthwise and 50-60 ridges over circumference). The rollers are having marginal clearance and rotate in opposite direction at different speed in the ratio of 1:10 between slow: high speed rollers. The speed of 70:700 and 100:1000 rpm have good effects. The crush, tear and curl (CTC) maceration takes only few minutes.

b) Orthodox processing: The rolling is done normally in 36” or 46” diameter rollers. A tea roller consists of 3 main parts; a table fitted with cones and battens, a bottomless jacket and pressure cup fitted with adjusting screw to enable pressure to be applied to a desired extent. The roller may be table or jacket moving, normally rotates at 45 rpm speed. The battens are provided to form obstruction in the leaf path. It increases frictional effect of roller table and breaks the leaf at the same time. Battens help in cutting the leaves in roller. The cone fitted at centre of table intensifies leaf circulation by causing a greater turning action provided by batten alone. 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.

4. Oxidation/fermentation: Oxidation begins once the leaf membranes are broken down enzymatically during the rolling process. It is an important stage in black tea processing. During this stage, the most important properties of tea are produced. It is a chemical process where oxygen is absorbed and the leaves turn progressively darker. The tannins are released and transformed during this process. Oxidation causes the leaves to turn bright copper in colour. This process is the main deciding factor to prepare different types of teas like Green, Oolong or Black tea. 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.

5. Kill-green and shaping: After oxidation, kill-green is done to stop tea leaf oxidation at a desired level. Heating tea leaves moderately deactivate their oxidative enzymes without destroying tea flavour. The leaves after kill-green are allowed to be lightly heated in a closed container, which causes the previously green leaves to turn yellow. The damp tea leaves are then rolled to be formed into wrinkle strips.

6. Drying: The leaves are then dried evenly and thoroughly without burning. Drying of leaves stops the oxidation process. The main objective of drying is to arrest fermentation and to remove moisture and produce good quality tea. This can be done in different ways including conventional drying, fluidized bed drying and air drying or baking. Curing/ageing: Curing is not required for all types of teas however, some type of teas require additional aging or secondary fermentation to enrich their drinking potential. Flavoured teas are manufactured by spraying with aromas - and flavours or by storing them with their flavourants.

Different types of tea: On the basis of manufacturing method, commercial tea is broadly classified as black tea, green tea, oolong tea, yellow tea etc. The basic difference is in the degree of fermentation adopted during manufacturing of tea from the Camellia sinensis evergreen plant. Brief detail about type of teas is as under:

1. Black tea: Black tea is the most common form of tea in Southern Asia (Sri Lanka, India, Pakistan, Bangladesh etc.) and many African countries including Kenya, Rwanda, Malawi and Zimbabwe. The Black tea process goes through the most stages of processing like withering, leaf maceration, fermentation, drying and grading. After picking, the leaves are left to wither for several hours and allowed to oxidize completely. Rolling or maceration is done to bruise and disrupt the leaf cell structures to release the oil which aid in oxidation. The last step consists of placing the leaves in an oven with temperature reaching up to 93.3^oC. When the leaves are 80% dry, the leaves complete their drying over wood fires. The final product is sorted accordingly to size, the larger size is considered "leaf grade," and smaller size "broken grade" which are usually used for tea bags. Black tea is further classified as either orthodox or crush, tear and curl (CTC) process tea.

2. Green tea: Green tea undergoes least amount of oxidation and the oxidation process is halted by quick application of heat, either with steam or by dry cooking in hot pans. Steaming of the leaves is done to prevent the leaves changing their colour from green to black and to inactivate the enzyme. It is followed by rolling. The leaves retain much of its original green colour especially the finer leaves whereas the older leaves have a blackish gray colour. For drying, the leaves are either stacked in hot air rack driers or are exposed to natural heat of sunlight. The tea is processed within one to two days of harvesting and retains most of the chemical composition of the fresh leaves in tea if processed properly.

3. Oolong tea: It is partially fermented tea. Oxidation is stopped somewhere between the standards for green and black tea. The fermentation period is short to change the colour of the leaf completely. The processing typically takes two to three days from withering to drying with a relatively short oxidation period. It is partially blackened. In oolong tea, the outer edge of the tea leaf is fermented while heart of leaf remains unfermented. The beverage is intermediate between those produced from green and black tea. The term "oolong" is used specifically as a name for certain semi-oxidized teas.

4. White tea: White tea is produced in lesser quantities than most other styles and is therefore, more expensive than tea from the same plant processed by other methods. It is mostly produced in China and is classified as organic or premium tea. It is produced from the young leaves or new growing buds that have undergone minimal oxidation. The oxidation is halted after a slight amount of wilting with heat. Leaf buds processed into white tea are usually dried immediately after wilting/withering.

5. Yellow tea: Yellow tea is processed in a similar manner to green tea but instead of immediate drying, leaves are stacked, covered and gently heated in a humid environment. This initiates oxidation in the chlorophyll of the leaves through non-enzymatic and non-microbial means, which results in a yellowish or greenish-yellow colour. This tea is popular in Japanese tea ceremonies due to its appearance and distinctive flavour.

B. COFFEE
Coffee is an important beverage used all over the world. Brazil and Columbia are the largest coffee producers in the world. Coffea arabica accounts for 75-80% of world production. The domestic consumption of coffee in India stands at 85,000 tonnes valued at about Rs 2292 crores. Coffee is harvested during dry season when the coffee cherries are bright red, glossy and firm. Picking is done by hand or by using machine. After picking, the coffee can be prepared either by dry method which produces natural coffee or by wet method which produces washed coffee.
Coffee is harvested in one of two ways:

a) Strip picked: The entire crop is harvested at one time. This can either be done by machine or by hand. In either case, all of the berries are stripped off of the branch at one time.
b) Selectively picked: In this method, only the ripe berries are picked individually by hand. Pickers rotate among the trees every 8-10 days, choosing only the cherries which are at the peak of ripeness. This method being labour intensive and costly is used primarily to harvest the finer arabica beans.

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 processing of coffee includes; dry method and wet method to produce unwashed and washed coffee respectively.

1. 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.

2. 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.

3. 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 287.8^oC and in this process the beans are kept moving to avoid burning. When the bean temperature reaches 209^oC they start turning dark brown and oil (called coffee oil or caffeol or coffee essence) start to emerge. This process is called Pyrolysis is the heart of roasting, as it produces aroma and flavour of coffee. After roasting, beans are cooled by air or water. The cooling must be quick in order to preserve the flavour, aroma and keeping quality.

4. 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.

5. 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.

6. 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. There is a prominent segment of consumer preferring decaffeinated coffee owing to health consciousness.

2. Estate Coffee: Production of good quality coffee by highlighting special features of estate can be classified as estate branded coffee. The estate coffee are generally more expensive and actually define the specialty coffee market.

3. Monsooned Coffee: These are prepared by the special natural process which possesses a special monsooned flavour, mellow taste and golden look. It is also produced in India. It is graded as Monsooned Malabar AA, Monsooned Basanally and Monsooned Robusta AA.

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) due to slower development of beans is called high grown coffee. 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. Arabica plantation coffee (worked coffee) is grown in the Mysore, Coorag and Billigiris regions. It is a premium coffee that represents the best quality coffee in India.

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. COCOA
Cocoa (Theobroma cacao L. family Sterculiaceae) beans are the primary raw material for confectioneries, beverages, chocolates and other edible products. Cocoa powder, butter and chocolate are the major products.
The harvesting of cocoa pods is done at 7-10 days interval and the harvested pods may be kept for 2-4 days before they are opened for fermentation. Hitting pods against hard surface may be adopted for opening of pods. The main characteristics of cocoa beans are initial moisture contents (52-55%), final moisture content (6-8%), fat contents (55-58%) and acidity of 5.8 percent. The pod husk contains 6-8% crude protein and 24-56% crude fibre.

Processing of cocoa: Curing is the process by which cocoa beans are prepared for the market. Curing involves two unit operations; fermentation followed by drying. Fermentation involves keeping cocoa beans well insulated so that heat is retained whole, at the same time air is allowed to pass through the mass. The process lasts up to 7 days and immediately followed by drying. The flavour of cocoa is developed only when it undergoes fermentation.

1. Fermentation: Fermentation of cocoa beans is essential to remove mucilaginous pulp, to develop flavour and aroma precursors, reduce bitterness, kill germ of seed and to loosen the testa. The cocoa pods after harvesting are cautiously opened. The beans and the mucilage are scooped out and subjected to natural fermentation. They are piled in heaps in perforated wooden bins for a period of 3-12 days. The heat produced during fermentation raise the temperature to about 45-60^oC. The fermentation is complete when temperature of mass begins to fall. At the end of fermentation, the pulp breaks down and the seed colour change from pale yellow to violet to brown. For fermentation the heap, box, tray and basket methods can be followed.

2. Drying: The fermented beans contain 33% moisture. They are dried to reduce moisture to 6-8% in sun or hot air dryers. During this process, the colour of the shell changes to dark brown. The dried beans are packed in polyethylene lined gunny bags and stored in a cool and dry place. The dried beans can be used for manufacture of different products (Fig 15.1)

Chocolate from cocoa beans
Important steps used for making chocolate from dry cocoa beans include roasting, grinding, refining, conching and tempering.
1. Roasting: The dried beans are cleaned, sorted and roasted at 150-160^oC for 40-50 minutes. Roasting develops characteristic flavour and colour. It also causes changes in chemical structure of polyphenols producing less astringency compound.

2. 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.

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

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

5. 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 80^oC 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.

6. 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.

D. ARECANUT (Areca catechu L.)
Arecanut is one of the most important commercial crops in South East Asia and is cultivated primarily for its kernels chewed in tender, ripe or processed form. Arecanut palm belongs to family Palmae. India is the leading country in production contributing to 51% of world’s total production followed by China (25%). The arecanut is used as raw or in processed form as it is an essential component of gutka and pan masala, whereas, chali supari or kalipak are some of the value added products. Kalipak is prepared from immature green nuts and chali is prepared from ripe nuts.

Preservation of arecanut: In Assam, fresh fruits are preserved in thick layer of mud and this product is known as ‘Bura Tamul’. In Kerala, fresh fruits are stored by steeping in water and the product is called ‘Neettadakka’. The inner core is well preserved by this method but discolouration of outer husk and foul smell due to bacterial attack are some drawbacks. Preservation of ripe nuts after initial heat blanching in a solution containing sodium benzoate (0.1%) and potassium meta-bisulphite (0.2%), acidified to a pH of 3.5 to 4.0 with HCl helps in eliminating the foul smell and improves the quality of nuts.


Processing of arecanut

1. Dried ripe nuts (Chali or kottapak): The dried whole nuts of arecanut are known as Chali or kottapak. The ripe nuts are dried in open sun for 35-40 days up to 12% moisture content and the marketing of whole nuts is done after dehusking. Dehusking can be done with manually operated dehusker developed by CPCRI, Kasargod. Depending upon the size, different grades of arecanut in decreasing order are moti, srivardhan, jamnagar and jini. Sometimes the fruits are cut longitudinally into 2 halves and are sun dried for 10 days. The kernels are scooped out and are given a final drying. The product is known as Parcha, which is popular in Kerala and Karnataka. Drying in mechanical drier takes 60-70 hours at 45-75⁰C.

2. Kalipak: This product is famous in Kerala and Karnataka. Tender nuts are dehusked, cut in to pieces, boiled with water or a diluted extract from previous boiling, coated with kali and dried. Kali is a concentrated extract obtained after 3-4 batches of boiling of arecanut. The kalipak is known by different names depending on number, shape and size of the cuts. Api or Unde (without any cuts), batlu (transverse cut into halves), choor (several longitudinal cuts), podi (both longitudinal and transverse cuts) and erazel (transverse thin slices). Lylon is another product made from green nuts which are cut transversely into 5-6 discs without kali coatings. A well dried product with dark brown colour, glossy appearance, chewing feel and absence of over-mature nuts are rated superior.

3. Scented supari: It is made both from chali and kalipak. Chali supari is more popular. The dried nuts are broken into bits and blended with spices for flavour and packed in butter paper. Saccharin is occasionally used for sweetening. Rose essence is commonly used for flavouring of supari. The scented supari is packed in aluminum or butter paper pouches for marketing.