Ripe cocoa pods on a Theobroma cacao tree

The cocoa tree and the threats it faces

Tom Freeman looks at Theobroma cacao, how we get chocolate from it, and its biggest enemy: black pod disease

Before chocolate existed, there was cocoa: a bitter drink made from the beans of the Theobroma cacao tree, treasured by the Maya, Aztec and Olmec peoples of Central America.

Spanish colonists were intrigued, and added spices and sugar to make the drink less bitter. The beans were shipped back to Europe, where cocoa went on sale in the late 16th century. At first, it was a luxury drink for the rich, but its price fell and it went mainstream. Rising demand led to cocoa plantations being established around the world.

People tried many ways of preparing cocoa, but the big innovation came in 1828, from Dutch father and son Casparus and Coenraad van Houten. They worked out how to separate cocoa into solids and fat. This made it easier to produce the drink, but also allowed further processing to make a solid bar of chocolate.

Other industrialists of the 19th century – Rowntree, Cadbury, Lindt, Nestlé, Hershey – developed specialised processes for making their own brands of chocolate. And brands they were: chocolate was marketed with great ingenuity. It has been sold as a tasty treat, an energy booster, a health food, an aphrodisiac and more.

And we bought it. Chocolate is now a huge global industry.

Producers and consumers

In 2013, 4.6 million tonnes of cocoa beans were produced worldwide – two-thirds of this in Africa. The biggest producers were Côte d’Ivoire (32 per cent), Ghana (18 per cent), Indonesia (17 per cent), Nigeria (8 per cent) and Cameroon (6 per cent).

The keenest consumers of chocolate are the Swiss, eating 9 kg each per year. The Germans are second with 7.9 kg, and the British and Irish are joint third with 7.4 kg. The Americans are ninth, eating 4.3 kg a year each.

From tree to treat: how to make chocolate

Theobroma cacao needs a humid, tropical climate with rich soil, shade and plenty of rain. Its flowers ripen into cocoa pods. Farmers slice these open and scoop out the juicy pulp and the cocoa beans. They leave the beans to ferment in the pulp for a few days, then dry them out for shipping.

At the factory, the beans are roasted, then each shell is cracked open and removed to leave the nib – the cocoa core. The nibs are ground to produce cocoa liquor, which is essentially what the Central Americans and Europeans were drinking before the Van Houtens’ innovation.

The liquor is separated into cocoa solids and cocoa butter. The solids are reduced to fine particles, which can either be sold as cocoa power or recombined with cocoa butter – more of it than the liquor naturally contained – to be made into chocolate. At this stage, milk, sugar and any other flavourings are added.

Then, to give the final product a good solidity, the liquid is repeatedly heated and cooled to change its crystal structure. Finally, it’s poured it into a mould to set, then wrapped and distributed to sweet-toothed consumers.

Black pod disease

But cocoa trees are at risk.

Several species of the water mould Phytophthora can make the cocoa pods blacken, shrivel and die. This black pod disease can also spread to the rest of the tree. Globally, up to 10 per cent of Theobroma cacao trees are killed by black pod disease every year, and 20–30 per cent of the cocoa crop is lost.

Phytophthora spores are carried by wind and water, and by insects, rodents and bats. When a spore lands on a pod or a leaf, it germinates and the infection begins. As well as spreading across the surface, the mould grows deeper into the pod, rotting it from the inside.

Farmers can do several things to reduce the spread of Phytophthora:

  • Plant trees a few metres apart, and prune them if their branches grow too close to each other.
  • Make sure planting sites have good drainage, so surface water doesn’t accumulate.
  • Cut off pods showing early signs of infection immediately. Remove them and destroy them.
  • Use pest control to stop animals spreading the disease.
  • Spray infected plants with certain copper-based fungicides.

Scientists are also trying to breed varieties of tree that have better resistance to black pod disease. Different strains of Theobroma cacao have different responses to the infection, which suggests this approach could pay off. But it may be hard, because resistance to one species of Phytophthora may not mean resistance to others.

Other dangers to chocolate

While black pod is by far the biggest disease of cocoa trees, it’s not the only one:

  • Witches’ broom: Moniliophthora perniciosa is a fungus that stunts the growth of flowers and pods.
  • Frosty pod rot: Moniliophthora roreri, another fungus, eats the pods from the inside.
  • Vascular streak dieback: The fungus Oncobasidium theobromae stops the leaves producing chlorophyll and can kill the whole tree.
  • Mirids: Also known as capsids, these insects – including species of Sahlbergella, Distantiella and Helopeltis – feed on the trees, causing leaves and branches to die.
  • Pod borer: The moth Conopomorpha cramerella infests the pods, where it lays its eggs.

The other big looming threat is climate change. As the world warms, the African countries that supply most cocoa are predicted to become drier, which will make it harder for the trees to grow. Growers may be able to adapt by moving to higher-altitude plantations or breeding trees with better drought resistance.

Lead image:

Luisovalles/Wikimedia Commons


Questions for discussion

  • What other major plant diseases are there? How are these being fought?
  • What would happen if black pod disease spread more widely?
  • Why do the countries that produce the most cocoa not consume very much of it?

Further reading

About this resource

This resource was first published in ‘Plants’ in May 2016.

Ecology and environment, History
Education levels:
16–19, Continuing professional development