Theobroma cacao (cocoa tree)
The cocoa tree is the source of one of the world’s most delicious and familiar products… chocolate.
About this species
The edible properties of Theobroma cacao were discovered over 2,000 years ago by the local people of Central America living deep in the tropical rainforests. In the year 2008-2009 the world cocoa production was 3,515,000 tonnes. This is equivalent to the weight of a line of double-decker buses stretching more than three times the length of Britain!
The scientific name Theobroma cacao was given to the species by the Swedish botanist Carl Linnaeus in 1753, when he published it in his famous book Species Plantarum. Theobroma means "food of the gods" in Latin, and cacao is derived from the Nahuatl (Aztec language) word xocolatl, from xococ (bitter) and atl (water).
Geography & Distribution
- Central America
- northern South America
Cocoa is native to Mexico, Central America and northern South America (Colombia, Ecuador, Venezuela, Brazil, Guyana, Surinam and French Guiana). It has also been introduced as a crop plant into many tropical African and Asian countries.
In its natural habitat, cocoa grows in the understorey of evergreen tropical rainforest. It often grows in clumps along river banks, where the roots may be flooded for long periods of the year. Cocoa grows at low elevations, usually below 300 metres above sea level, in areas with 1,000 to 3,000 mm rainfall per year.
Cocoa pods on the tree at Kew
Cocoa is a spindly, evergreen tree 5 to 8 m tall, found growing in the shade of giant trees occupying the top layer of the rain forest. It has a taproot, which penetrates far below the soil surface.
Its dark green leaves are shiny, leathery, egg-shaped or elliptic in shape and 20 to 35 cm long and 7 to 8 cm wide. The leaf surfaces are hairless or covered in scattered star-shaped hairs. The base of the leaf is rounded or heart-shaped, and the tip is long and drawn out allowing water to drip from it.
Cocoa flowers are small, yellowish white to pale pink, and grouped together in clusters arising directly from the trunk (cauliflory).
Flowers are produced throughout the year. In the wild, cocoa trees are pollinated by midges, and only about 5% of flowers receive enough pollen to start fruit development. When they are pollinated there is a dramatic change as the tiny flowers develop into massive cocoa pods.
The fruit is an egg-shaped red to brown pod, 15 to 25 cm long, with a more or less knobbly surface and lines from top to bottom. The pod contains 30 to 40 seeds, each of which is surrounded by a bitter-sweet white pulp. In the wild the seeds are dispersed and eaten by different mammals like agutis and monkies. When the seeds are dried and fermented in the sun they are brownish red, and known as cocoa beans.
The genus Theobroma
The genus (the cocoa species and its siblings) Theobroma consists of 22 species, including the Brazilian species Theobroma cupuacu, which provides a bitter-sweet pulp widely used in juice drinks in the Amazon. The Malvaceae family, of which cocoa is a member, contains many economically useful plants. These include cotton (Gossypium hirsutum), ornamental Hibiscus species, okra (ladies fingers, Hibiscus esculentus), Ceiba and Bombax species (from which kapok fibre is derived), durian fruit (Durio zibethinus) and balsawood (Ochroma pyramidale).
The history of chocolate
The edible properties of Theobroma cacao were discovered over 2,000 years ago by the indigenous people of Central America living deep in the tropical rainforests.
The Olmecs living in Mexico and Guatemala established their first cacao plantations around 400 BC, and by 250 AD the Mayans depicted cocoa in their elaborate hieroglyphic writings and on carvings and paintings.
Historical accounts about also point to widespread use of chocolate in Maya and Aztec engagement and marriage ceremonies and religious rituals. In this respect chocolate occupied the same niche that expensive French wines and champagne do in European culture today.
The Aztecs and Maya peoples had many ways of making food and drink from cocoa beans. They also used the beans as money, for example exchanging one turkey for 200 beans, or one slave for 100 beans.
Cocoa beans were so precious that only the royals, warriors and the wealthy could afford to eat and drink chocolate. The hieroglyphs tell us that the Aztecs and Maya peoples drank cocoa powder suspended in water, and used flavourings such as chillies (Capsicum annuum), vanilla (Vanilla planifolia), achiote (Bixa orellana), aromatic herbs and honey.
From Columbus to Cadbury
Chocolate was seen in Mexico by Christopher Colombus in August 1502. It is said that he came across a large canoe loaded with some small beans that looked to him like goat droppings, and that he paid them little attention! However, once Spanish explorers discovered its decadent delights in the 1520s, they brought cocoa beans home, sweetened the water-based recipe and spread this delicacy throughout Europe. By the middle of the 17th century sweetened hot chocolate was very popular throughout Europe, especially among the elite.
Cocoa arrived in the British Isles in the 1650s, which was more or less at the same time as coffee. With Cromwell’s forces Britain took over the control of Jamaica from the Spanish. At the time cacao plantations were already flourishing there, and these became the main source of British chocolate.
The story goes that the first person to dissolve cocoa in milk was the British medical doctor and avid collector, Sir Hans Sloane. As a young man, he was stationed as a doctor in Jamaica where he collected the very chocolate plant that Carl Linnaeus used to give chocolate its scientific name. Hans Sloane, also a clever businessman, later sold the idea to the Cadbury family. Hans Sloane’s collections later founded the British Museum, and his chocolate specimen can be seen on display in the Darwin Centre in the Natural History Museum in London.
What a cocoa bean is made of
Cocoa beans possess 45-53.2% fat in the form of cocoa butter (also known as theobroma oil) which is made up of a variety of fatty acids.
Cocoa beans contain up to10% of phenols and flavenoids which are antioxidants potentially inhibiting cancer or cardiovascular diseases, as well as potassium, magnesium, calcium and iron. Additionally, they contain 1-3% theobromine and caffeine, alkaloids that stimulate the central nervous system. Caffeine has a positive effect on mental alertness, for instance when taken in caffeinated drinks.
The ingredients for chocolate – cocoa powder and cocoa butter (solids) – are prepared from fermented and roasted cocoa seeds. A typical bar of milk chocolate contains around 15% cocoa liquor and 20% cocoa powder. The distinctive flavour of chocolate develops during the fermentation process.
Chocolate is more than just a delicacy; evidence suggests that eating between 46 and 105g chocolate a day can have a moderate effect on lowering blood pressure.
Cocoa has been used for an array of medicinal purposes. Unfermented cocoa seeds and the seed coat are used to treat a variety of ailments, including diabetes, digestive and chest complaints. Cocoa powder, prepared from fermented cocoa beans, is used to prevent heart disease. Cocoa butter is taken to lower cholesterol levels, although its efficacy is unclear.
It is also used widely in foods and pharmaceutical preparations, as well as being used as a rich moisturiser for the skin.
Alternative to peat mulch
The crushed shells of cocoa beans are used as an alternative to peat mulch. Mulches are layered on to the soil surface to suppress weeds, conserve moisture, improve its visual appearance and minimize erosion. Not only does this make good use of cocoa-shell, which is a by-product of the chocolate industry, but it also helps reduce the use of peat.
Peat bogs are important sites for wildlife and also help to protect the earth from global warming. In Great Britain, over 94% of the 69,700 hectares of peat bogs have been damaged or destroyed. Most of this damage has occurred in the last 50 or so years, since the promotion of large-scale use of peat for the horticultural industry, which now discourages this.
Millennium Seed Bank: Seed storage
Kew's Millennium Seed Bank Partnership aims to save plant life worldwide, focusing on plants under threat and those of most use in the future. Seeds are dried, packaged and stored at a sub-zero temperature in our seed bank vault.
As the seeds of the cocoa tree are recalcitrant (meaning that the seeds are not amenable to long term frozen storage as they would not survive drying to the required levels in the seed bank), it is not possible store this kind of seed in a seed bank. Conservation of cocoa varieties therefore rely entirely on live trees in plantations and in the wild.
Flowers of Theobroma cacao (Image: Wolfgang Stuppy)
Theobroma cacao grows best under tropical conditions, with strong light and high humidity. A loam-based compost with plenty of organic matter (such as coir) should be used. The tree should be kept moist and the foliage damped-over daily, except during sunny weather when scorching may occur. Soft water should be used to prevent limescale deposits on the leaves. Mulching around the base of the tree with well-rotted compost will help the soil to retain moisture and prevent weeds. A balanced liquid of leaves should be given during the summer and high potash during the winter, once a week. Pruning should be carried out to maintain the required shape.
Cocoa can be propagated by seed, using a propagator set to a temperature of 22 to 23 ˚C. Germination should take between 10 and 14 days. The seedlings grow very quickly and require regular potting up. Flowers are borne on the old wood of the tree, and are pollinated by ants at Kew, although hand-pollination using a paintbrush is possible. Once the tiny flowers are fertilised, the fruit grows into the familiar cocoa pod. Growing-on temperatures in a glasshouse should be 22 to 24 ˚C during the day and 18 ˚C during the night. Cocoa is prone to glasshouse pests, such as mealy bug and scale insect. These can be kept in check by using biological controls or systemic insecticides. Small infestations can be dealt with using alcohol and a paint brush.
In 2008-2009 the world cocoa production was 3,515,000 tonnes. This is equivalent to the weight of a line of double-decker buses stretching more than three times the length of Britain! Despite the fact that cocoa is native to tropical America, world production (2008-2009) is spread as follows: West Africa 71%, Central and South America 13%, Southeast Asia 16%.
A number of different cocoa cultivars are grown commercially, and these have historically been divided into three main groups:
- The Forestero group is cultivated in West Africa and Brazil and represents 80 to 90% of the world’s cocoa plantations. In these cultivars the fruit is rounded and almost smooth, and the pod husks are hard and green with 30 or more seeds per pod.
- The Criollo group represents about 10% of the world’s cocoa plantations. Its importance is on the wane, but it is still grown in the Caribbean, Venezuela, Ecuador and Papua New Guinea. It is, however, the most highly appreciated and the Criollo beans have always been used for the best quality chocolates. The yellow or red pod husks are soft and thin and there are 30 or more seeds per pod.
- The Trinitario group is a good quality hybrid between Criollo and Forestero, with a good, but less intense, aroma than Criollo beans. Trinitario husks are hard and thick, and variable in colour, with 30 or more seeds per pod.
Cocoa at Kew
Theobroma cacao dried specimen collected in Bahia (Image: RBG Kew)
Theobroma cacao can be seen in Kew’s Princess of Wales Conservatory, and also in the Palm House, which displays plants from tropical rainforests, including those of economic value such as banana (Musa), rubber (Hevea), cotton (Gossypium) and coffee (Coffea).
There are 107 specimens of Theobroma cacao in the Economic Botany Collection, one of the behind-the-scenes areas of Kew. These include samples of bark, shells, beans, cocoa butter, cocoa liquor, nibs (the dried and roasted kernel of the cocoa bean that remains after the husk has been removed), pods, powder, fruit, paste, leaves, flowers and even a carved wooden elephant. These items can be examined by appointment to bona fide researchers from around the world. To view a selection of this collection and to discover more about the chocolate tree, visit the Plants+People exhibition in Museum No. 1.
The Herbarium at Kew contains both dried and alcohol-preserved specimens of Theobroma cacao. The details of 12 of these can be viewed in the Herbarium Catalogue. These include images of specimens from the herbaria of George Bentham (1800-1884, author of the classic Handbook of the British Flora) and William Hooker (1785-1865, Kew’s first official Director).
Flowers and Fruit of the Cocoa Tree, painted at Singapore by Marianne North (Image: RBG Kew)
Find out more
Kew Today 22 Dec 09 – cacao tree in fruit
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