Growing cocoa

Cocoa tree pruned to a single jorquette
Cocoa tree pruned to a single jorquette.

Currently cocoa is not commercially cultivated in Australia.

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About the cocoa tree

Cocoa (Theobroma cacao) is a tropical tree crop originating from the Amazon basin where it grows in the shaded rainforest understorey and can reach 20 m in height. The tree produces pods that contain about 40 cocoa beans surrounded by a sweet tasting pulp. When fermented and processed, the beans produce one of the most desired flavours in the world - chocolate.

Cocoa seedlings have a single main stem that grows vertically to a height of 1-2 m. The bud then forms three to five branches (the jorquette) that grow out at an angle as fan branches. Further upright suckers (chupons) emerge below the jorquette and grow up through the fan branches forming more jorquettes and further whorls of fan branch growth. In this way the tree becomes higher, forming several layers of jorquettes, each successively weakening and eventually fading out.

The root system of a mature tree comprises a taproot up to 2 m long and a dense system of lateral roots in the top 20 cm. These roots spread out to lengths of 5-6 m forming a dense surface-feeding mat.

Flowers arise from cushions in the wood of the main stem and fan branches once they are at least two to three years old. Only 1-5% of flowers are successfully pollinated and form pods. Pollinating insects are mainly tiny midges that require cool, dark, moist habitats and breed in rotting vegetation.

Even though only a small percentage of flowers are pollinated, the tree sets too many fruit to carry to maturity. Cocoa has a fruit thinning mechanism where the young fruit (cherelles) stop growing, turn black and shrivel, but do not fall off the tree. This is called cherelle wilt and is often mistaken as a disease situation. The remaining pods take five to six months to ripen after pollination. Ripe pods also do not fall off the tree.

History

For many centuries, the Mayas in South America harvested cocoa from the wild for use in religious ceremonies. In Central America, the Aztecs used cocoa to make a thick chocolate style drink and cocoa beans were used widely as currency. It is not known how cocoa originally reached Central America, but after the conquest of Mexico, cocoa cultivation spread to the Caribbean, then across the Pacific to the Philippines, the East Indies and India. Cocoa also began to be cultivated in Brazil and from there it was eventually taken to Africa in the 19th century.

European nations gradually became aware of cocoa in the 17th century. When the Swiss developed milk chocolate manufacturing late in the 18th century, increased consumption stimulated the demand for cocoa, which led to widespread cultivation. In the 20th century, production increased rapidly - from less than 125,000 tonnes in the early 1900s to a record 3,100,000 tonnes in 1999-2000. Cocoa has become a major commodity crop and, by value, it is now the seventh largest food commodity traded globally.

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Climate requirements

Climatic and site requirements place cocoa in the tropical regions of the world generally within 15° of the equator. This region is predominantly underdeveloped and highly populated, and cocoa production has evolved with access to cheap and plentiful labour. Irrigation is rarely used and planting has been restricted to regions with reliable, year round rainfall.

Cocoa is usually grown under remnant forest, planted shade trees or intercropped with other commercial crops that protect the cocoa. In Malaysia and Indonesia, cocoa is also grown in full sun, although shade is used during establishment. The height of cocoa is kept to about 3-5 m to make management and harvesting easier. Average yields are low, about 1 tonne/ha or less of dry beans. Harvesting has a high labour demand for a relatively short and often unpredictable season. After harvest, beans are fermented and dried by growers or at a central fermentary, and then traded.

About 70% of world production is grown by smallholders on a low input, low output basis. Typically, family or village labour is used at relatively little cost. Trees can be individually managed and the quality of bean fermentation is usually assured. As a rule of thumb, one labourer is required per 2.5 ha of established cocoa in traditional production systems.

Remaining production is on plantations of about 20 ha and upwards. Only recently have plantation companies running large-scale operations grown cocoa. Cocoa does not offer the advantages of other crops grown under estate-style management systems. It does not require substantial capital expenditure on processing equipment and industrialised fermentation has generally compromised quality. Also, labour productivity on plantations is critical to profitability, but there has been no determined effort to mechanise cultural practices. To be competitive with smallholders, plantation cocoa must achieve higher average yields and this requires higher levels of inputs for sustainability.

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Environmental requirements

Temperature

The ideal range of temperatures for cocoa is minimums of 18-21°C and maximums of 30-32°C. Commercial cocoa production is limited to where the average minimum in the coldest months is greater than about 13°C. If the absolute minimum temperature falls below 10°C for several consecutive nights, the yield is likely to be reduced. Defoliation and dieback occurs between 4-8°C.

Although cocoa will grow above 32°C, the upper temperature limit is not well defined and shade cover will influence maximum temperatures for the cocoa. High temperatures may affect bean characteristics and yield.

Rainfall

The distribution of annual rainfall for regions in which cocoa is grown is 1250-3000 mm per year. The rainfall must be well distributed and any dry period should be no longer than three months. Annual rainfall greater than 2500 mm may result in a higher incidence of fungal diseases. Irrigation is rarely used and information on growing cocoa under irrigation is limited.

Soils

Cocoa is grown on a wide range of soil types, but soils with moderate to high fertility are favoured since fertiliser inputs under traditional production systems are low. The main requirements are:

  • 1.5 m depth of free draining soil
  • good moisture holding capacity
  • pH range from 4.5 to 7.0, preferably close to 6.5.

Wind

Attempts to establish cocoa without shade often fail and one of the main causes is wind damage. Cocoa prefers calm conditions and persistent moderate wind can cause problems during establishment. Young vigorous plants can be bent over and new leaves can be broken at the axils.

Because cocoa is not generally grown in areas prone to cyclones, its vulnerability to strong winds is not well known. However, it is supposed that it would suffer less damage than many tropical tree fruit crops due to its relatively small stature and higher density planting. Fallen trees are capable of recovering as they can regrow from a basal shoot.

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Propagation and land preparation

Seedlings are generally used for planting. They are raised in nurseries where shade, wind protection, nutrition and irrigation are provided. Hybrid seeds are often sourced commercially, but even with these, the plants raised can be highly variable in growth and performance. Seed is collected from ripe pods and, if the fresh beans are planted immediately, at least 90% should germinate within two weeks. Planting of seed directly to the field is not practiced due to lack of irrigation and problems with weed and pest management.

Vegetative propagation is used where selected characteristics are desired. The trees raised are much more uniform in growth and performance than those raised from seed. Various techniques, including rooted cuttings, budding and grafting are used. Cocoa presents special problems for in-vitro propagation and reliable, economic methods for mass tissue culture propagation have not been developed.

Establishment

Young cocoa plants may be field planted after three to six months. Because establishment without shade is rarely successful, shade must be well established prior to field planting. As well as sun protection, the shade reduces wind exposure and provides a better microclimate. Shade strategies include:

  • retaining remnant forest
  • planting temporary and permanent shade species
  • interplanting with species that also provide a commercial return.

Shade removal is possible after three to four years. In many situations windbreaks will be beneficial or necessary.

Planting density depends on:

  • tree vigour
  • light interception
  • the farming system.

It may range from 800-3000 trees/ha with about 1200 trees/ha being common in Malaysia under permanent shade.

Nutrition

About 200 kg N, 25 kg P, 300 kg K and 140 kg Ca are needed per hectare to grow the trees prior to pod production. For each 1000 kg of dry beans harvested, about 20 kg N, 4 kg P and 10 kg K is removed. If the pod husks are also removed from the field, the amount of K removed increases to about 50 kg.

Soil and leaf analyses can be used to determine the nutritional needs of cocoa. There are some problems with leaf analyses due to the difficulty in sampling leaves of the same age and the influence of shading on the nutrient composition of leaves. Visual symptoms of mineral deficiencies are well documented and can be used as a qualitative guide to fertiliser requirements.

Pruning

Cocoa propagated from seed is pruned to develop the preferred structure shown in the above picture. Pruning is mainly used to limit tree height. The first jorquette should be formed at 1.5-2 m. Further chupons (suckers) are continually removed preventing subsequent jorquettes and restricting further vertical growth. Some pruning of fan branches may be required to maintain evenness in the structure and remove low hanging branches. The end result is the formation of a tree with a canopy at a convenient height for management. Vegetatively propagated plants have a different structure and will require different management. There is little evidence of the value of pruning strategies to promote high yields. Mechanical pruning (hedging) is not practiced.

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Harvesting and processing

Harvesting and bean extraction

Cocoa harvest is not limited to one discrete period, but spread over several months, and in some regions there may be pods available for harvest throughout the year. Typically, there are one or two peak harvest periods influenced by flowering in response to rainfall. However, temperature and the crop already on the tree will also influence flowering so that the yearly-cropping pattern can vary in areas with relatively uniform climate.

On ripening, pods turn from green or deep red to yellow or orange. Only the ripe pods that have changed colour are harvested. However, the timing is not critical since under-ripe pods will ferment satisfactorily and ripe pods can be left on the tree for two to three weeks. After this, pods may rot and the beans may germinate inside the pod. Harvesting is done by hand using machetes or knives to cut pods from the tree since pulling the pods from the tree can damage the flower cushion and tear the bark.

After harvest, the pods are opened to extract wet beans and this can be done immediately or delayed for up to several days. This is also a manual operation - usually the pod is cut open and the beans are scooped out by hand. The placenta, which joins the beans inside the pod, is preferably separated from the wet beans prior to fermentation. Machines have been developed for pod breaking and bean extraction, but have not been adopted because of difficulty in separating the wet bean from broken pod fragments or because they have not suited the needs of cocoa growing operations.

Fermentation and drying

Fermentation and drying are the last operations carried out on-farm prior to the trading of dried beans. Fermentation is essential for the development of chocolate flavour (further developed during roasting of the beans). After extraction, the wet beans are bulked together and gradually heat up as a result of exothermic chemical reactions in the pulp caused by the activity of microorganisms. Initially, the mucilage is broken down and drains off as sweatings. After 36-72 hours the beans are killed and a series of chemical changes take place inside the bean, some of which continue during drying.

Although chemically complex, methods of fermentation are simple. Fermentation is carried out in specially constructed wooden boxes, in heaps covered by banana leaves or in baskets. Much of the heat generated is retained by insulation, but this is more difficult with small quantities of beans and a minimum of about 90 kg is required when using traditional heap or box methods. The process usually takes from five to seven days to complete depending on the type of cocoa being grown and local practice. The mass of beans is turned or stirred at least once for aeration.

Fermented beans are then dried in the sun or artificially to a level that is safe for storage and transport (6-7% moisture content dry basis). Artificial drying can cause beans to be very acidic if they are dried too quickly. Dried beans are hand sorted or mechanically sieved and winnowed to remove defective beans and debris.

The 'pod index' expresses the number of pods required to produce one kilogram of dried beans. A low pod index usually means good bean size and a saving in harvesting costs since there is a high weight of beans per pod. The 'recovery' is the proportion of dry fermented beans to wet unfermented beans expressed as a percentage. It ranges from about 40% for under-ripe pods to 45% for over-ripe pods, but is also affected by variety and season.

Processing

The manufacturing of cocoa into the principal ingredients used in chocolate and by-products is generally an industrial process requiring expertise and specialised equipment. Physical characteristics assessed by manufacturers to determine the quality of cocoa beans (in addition to flavour attributes) are of relevance to growers. The average bean weight is expected to be 1.0-1.2 g, corresponding to a 'bean count' of 100-83 beans per 100 g. A low shell percentage is desirable as shell is removed in manufacture and has no value - 11-17% is typical. The fat content of the cotyledons (nib) is important since cocoa butter has a high value - at least 53% is preferable.

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Further information

Producing horticultural crops

Last updated 10 March 2010