Large Cardamom: Harvesting and Post Harvest Technology

2016

First crop comes to harvest about 2–3 years after planting of sucker or seedling. However stabilized yields are obtained only from the 4th year up to 10–12 years. Sustainable yield depends on proper plantation management like regular rouging coupled with replanting, weeding, mulching plant bases, winter/summer irrigation, shade regulation etc. Harvesting season starts in August/September in low altitudes and continues up to December at high altitudes. Usually harvesting is done in one round and hence the harvested produce often contains capsules of varying maturity. Harvesting is done when the seeds of top capsules in the spike attain dark gray color. A special type of knife, locally known as Elaichi chhuri is used for harvesting. The stalk of the spike is cut very close to the leafy shoot. After harvest, individual capsules are separated manually. Capsules after harvest are cured to reduce moisture level to 10–12 per cent. The traditional curing is called Bhatti curing system (direct heat drying). Large cardamom is also cured by flue pipe curing system (indirect heat drying).

Bhatti system

Drying of cardamom is generally done in kilns locally called Bhatti. A Bhatti consists of a platform made of bamboo mats/wire mesh, laid over a four-walled structure made of stone pieces with a V shape opening in the front for feeding fire wood. Capsules are spread over the platform and are dried by direct heat generated from the firewood. About 70–80 kg of firewood is required for curing 100 kg of green cardamom in this traditional kiln (). Both green and dry woods are used and, as a result, huge volume of smoke is generated that passes through cardamom (). Depending on the thickness of the cardamom spread, it takes 60–72 h for curing (). Color of cardamom cured under this system is dark brown or black. If smoke percolates through cardamom, it loses original color, gets smoky smell and fetches low price ().

Portable curing chamber

This is a prototype of ‘Copra dryer’ developed at CPCRI (ICAR), Kasaragod, Kerala. The unit comprises of an air heating chamber and a furnace cylinder with chimney. The whole unit is fitted in a detachable angular iron frame. The air-heating chamber is enclosed by asbestos sheets on all the four sides leaving the top open for drying. Some space is left below the walls for air to enter into the heating chamber. Fresh cardamom is spread on the platform (wire mesh of size 3–5 mm) to a thickness of about 15–20 cm layer. Firewood is burnt inside the furnace cylinder. Air around the furnace gets heated up quickly and convected upwards and passes through the produce there by drying it. The temperature of the heating chamber is regulated by the rate of burning of firewood and also by regulating the chimney valves. It takes about 20 h for curing of about 50 kg raw capsules ().

Flue pipe curing system

In order to overcome the drawbacks of the Bhatti curing, a system known as “flue pipe system” has been introduced by the Spices Board of India for Large cardamom curing (). This method of curing requires a construction with corrugated tin sheets as roof and fitted with furnace, flue pipes, chimney ventilation system etc. Flue pipes made of galvanized iron sheets of 20 gauge, of 25 cm radius are provided in the room which runs from one end to the other along the center of the room below the wire gauge fittings. One end of the pipe is connected to the furnace, the firing place and the other end to a chimney to lead the smoke up through the roof into the air. Ventilators are provided in the room to lead water vapour out in the process of drying. An arrangement is made to keep a thermometer for reading the inside chamber temperature, from outside and accordingly ventilation as well as charging of fuel is regulated.

Cardamom is spread over the wire mesh floor and shelves in one or two layers after the chamber is kept at 40 °C. As soon as cardamom spreading is over, the curing room is kept closed and hot air is passed through the furnace into the flue pipes, bringing the room temperature to 45–50 °C. This temperature is maintained for about 3–4 h. At this stage, sweating of capsules takes place and moisture is released. Ventilators are then opened for sweeping out the accumulated moisture completely from the chamber. Ventilators are then closed and temperature is again maintained at 40 –45 °C. For uniform drying, cardamom is stirred one or two times. It is important to note that curing once started should be a continuous process till the drying is over. The whole process of curing takes about 28 to 29 h. Cardamom capsules thus cured are immediately collected and rubbed in trays or processed in Cardamom Polishing Machine for removing the tail (). Clean produce is then packed in polythene lined gunny bags and stored in wooden boxes. Cured cardamom on an average gives 25 per cent by weight of fresh cardamom ().

Cardamom dried in this method of curing has following advantages over those of the Bhatti system ().

(i) Original color (pink) and flavor (sweet camphor aroma) is retained.

(ii) Fetches better market price.

(iii) Curing expenses are low. Firewood consumption is less.

(iv) Total curing takes only 28–29 h.

(v) Uniform drayage is ensured.

Natural convection dryer

A dryer similar to the one described above was designed by CFTRI (). The dryer consisted of (i) a furnace, (ii) flue ducts, (iii) wire mesh tray for charging capsules and (iv) supporting structures. The furnace is fabricated using 8 mm thick MS sheets. A brick lining inside the furnace provides insulation. Flue ducts are made of 1.6 mm GI sheets, and the ducts were arranged in two tiers, one over the other, with sufficient space between them. Two crimped steel wire mesh trays with border were placed one over each duct. Firewood is burned in the furnace. The hot flue gases passing through the ducts set up convection currents in the air between the duct wall and wire mesh trays. The convection currents pass upward through the mesh and the bed of cardamom capsules on the mesh are subjected to drying.

This dryer has thermal efficiency of 5.6, better than the conventional flue curing kilns. It can dry 300 kg large cardamom at a time and for drying to a level of 10 per cent moisture the time required is 24 h, much better than the conventional method ().

Gasifier system of curing

It is an up gradation of the Bhatti curing system, developed by TATA Energy Research Institute, New Delhi. The solid fuel i.e. firewood through biomass gasification and thermo chemical reaction is converted into gaseous fuel by partial combustion. A mixture of producer gas consisting of CO (Carbon monoxide), H2 (Hydrogen), CH4 (Methane), CO2 (Carbon dioxide) and N2 (Nitrogen) is obtained, which is combustible and is used to burn. Through updraft type of biomass gasifier, air enters the gasifier from bottom and producer gas is taken out from top for curing cardamom.

A prototype unit, which is fitted in the existing Bhatti curing system, is successfully field tested in Sikkim and an improved quality large cardamom with better appearance and more volatile oil content is obtained ().

Gasifier system has definite advantages over the traditional Bhatti curing, the uncontrolled burning of wood logs in Bhatti system results in (a) loss of volatile oil; (b) exposure to smoke imparts a smoked-smell to the volatile oil and (c) charring of capsules due to localized over heating. But the controlled burning in a gasifier system of curing helps in (a) retaining more volatile oil; (b) better quality of volatile oil without any burnt or smoking smells due to clean burning of gaseous fuel and (c) the cured capsules retain the natural pink color of large cardamom ().

Chemical composition

Large cardamom seeds (dried) on analysis gave the following results: moisture (8.5 per cent), protein (6 per cent), volatile oil (2.8 per cent), crude fiber (22 per cent), starch (43.2 per cent), ether extract (5.3 per cent), alcohol extract (7 per cent) and (4 per cent). They are found to contain (for 100 g seeds), calcium 666.6 mg, magnesium 412.5 mg, phosphorous 61 mg, fluoride 14.4 ppm. The seeds contain the glycosides petunidin 3,5-diglucoside, leucocyanidin 3-O-β-D-glucopyranoside and subulin, an aurone glucoside. Cardamomin – a chalcone, alpinetin – a flavanone, are also reported ().

The powdered seeds on steam distillation yield 1–3.5 per cent of a dark brown, mobile essential oil. A study has shown that the volatile oil content was 2.44 per cent in Sawney, 2.42 per cent in Pink Golsey, 2.25 per cent in Ramnag and 1.66 per cent in Ramsey (). The oil has the following properties: sp. gr (20 °C): 0.9142, ref. index (26 °C); 1.46, optical rotation: 18 °3; acid value 2.9; saponification value 14.53; and saponification value after acetylation 40.2.

Large cardamom oil is characterized by flat cineol odor, harsh aroma and inferior flavor as against the warm spicy, aromatic odor of cardamom (). The Large cardamom oil is almost devoid of α-terpinyl acetate, and is very rich in 1,8-cineole ().

 

Selections from the book: “Cardamom. The genus Elettaria”. Edited by P.N. Ravindran and K.J. Madhusoodanan. Series: “Medicinal and Aromatic Plants — Industrial Profiles”. 2002.