Theobroma cacao

• 1. Introduction

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  Theobroma cacao is a tree that produces thousands of flowers and surprisingly little fruit. A mature tree may open 6,000 blossoms in a single year. Only about 20 of them mature into pods. Those few pods hold the seeds that become chocolate.

  This documentary follows the tree from its odd little flowers to its DNA. Who first domesticated it, and what did they want from it? Why did ancient empires treat its beans as money and as an offering to the gods? And what are scientists doing now to keep it alive as the climate grows more extreme?

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• 2. Flowers on the Trunk

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  On a cacao tree standing 6-12 meters tall, the blossoms cluster directly on the trunk and the older branches. Botanists call this habit cauliflory. Each flower is small, only 1-2 cm across, with a pink calyx. The evergreen leaves are alternate and unlobed, 10-50 cm long and 5-10 cm broad. The tree belongs to the mallow family, Malvaceae.

  Most of the world's flowers depend on bees, butterflies or moths. Cacao is different, because its pollinators are tiny biting midges of the genus Forcipomyia. When growers relied on these natural pollinators, the trees set more fruit than when pollination was done by artificial means.

  A ripe cacao pod is egg-shaped, 15-30 cm long and 8-10 cm wide. It turns from yellow to orange as it ripens and weighs about 500 grams. Inside, between 20 and 60 seeds, usually called beans, lie embedded in a white pulp. That pulp tastes like lychee or tropical melon. Some countries turn it into juice, smoothies, jelly and cream. Fermented pulp can even be distilled into an alcoholic drink, a use that was usually ignored until practices changed in the 21st century.

  Each seed is 40-50% fat, which is the cocoa butter. The seeds also carry theobromine, a stimulant similar to caffeine. That compound will turn up again as a chemical fingerprint in ancient pottery.

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• 3. Food of the Gods

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  Two Greek words, theós for god and brôma for food, were joined to make the name Theobroma, which means food of the gods. The species half of the name comes from the Americas. Cacao is the Spanish form of a word shared across Mesoamerican languages. Speakers of Tzeltal, K'iche' and Classic Maya said kakaw. Sayula Popoluca speakers said kagaw. In Nahuatl the word was cacahuatl, meaning bean of the cocoa tree.

  The Swedish naturalist Linnaeus fixed the pairing in 1753. His new binomial system of classification coined the genus and species Theobroma cacao. English speakers still use two spellings. The tree and its seeds are generally called cacao, though the word cocoa sometimes stands in.

  Cacao is one of 26 species in the genus Theobroma, which sits in the subfamily Byttnerioideae of the mallow family. In 2008, researchers proposed sorting cacao into 10 groups using form, geography and genomic evidence. Each group is named for its place of origin or a traditional cultivar. They are Amelonado, Criollo, Nacional, Contamana, Curaray, Cacao guiana, Iquitos, Marañon, Nanay and Purús.

  Iquitos, one name on that list, is also a real place in Peru. It becomes important again when scientists go looking for the tree's birthplace.

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• 4. Cradle in the Amazon

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  At a site called Santa Ana-La Florida, in Zamora-Chinchipe Province in what is now southeast Ecuador, the Mayo-Chinchipe culture domesticated cacao at least 5,300 years ago. From there the tree was introduced to Mesoamerica.

  Genetic work points toward the same corner of South America. Researchers once debated two domestication centres, one in the Lacandon Jungle of Mexico and one in lowland South America. Patterns of DNA diversity have since weakened that idea. One study sampled 1,241 trees and sorted them into 10 distinct genetic clusters. Around Iquitos, in the region of modern Peru and Ecuador, several clusters originated more than 5000 years ago. That origin led to the Nacional bean. The authors concluded that domestication probably began there, and probably for the pulp, which people ate as a snack and fermented into a mildly alcoholic drink.

  A second study combined DNA with climate models. It traced the greatest genetic diversity to a bean-shaped region covering Ecuador, the Brazil-Peru border and the southern part of the Colombian-Brazilian border. At the peak of the last ice age, 21,000 years ago, suitable habitat for cacao shrank to its smallest. This region still suited the tree, so it served as a refuge.

  Cacao grows well beneath the canopy of humid forest, and abandoned cultivated trees do the same. That makes it hard to tell a truly wild tree from one whose parents may once have been planted.

  A 2018 analysis of the genomes of cultivated trees complicated the picture. It concluded that all domesticated cacao descends from a single domestication event about 3,600 years ago, somewhere in Central America.

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• 5. Vessels and Rituals

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  A Mokaya archaeological site on the Pacific coast of Chiapas, Mexico, holds the earliest evidence of a cacao beverage in Mesoamerica, dating to 1900 BC. A vessel from an Olmec site on the Gulf Coast of Veracruz shows cacao being prepared by pre-Olmec peoples as early as 1750 BC. Both belong to the Early Formative period, which ran from 1900 to 900 BC.

  Chemistry supplies much of the proof. Residues in vessels from Puerto Escondido, Honduras, dated to 1100-900 BC, contained theobromine and caffeine. So did middle Formative vessels from Colha, Belize, dated to 600-400 BC. Researchers used similar techniques on four Classic period vessels from a tomb at the Maya site of Rio Azul, from around 400 AD. Cacao is the only known Mesoamerican commodity containing both compounds, so the pots very likely held cacao drinks. One Rio Azul vessel also carries a hieroglyphic text naming cacao.

  Physical remains are sparser. Whole beans were recovered at Uaxactun in Guatemala. Preserved wood from cacao trees came from the Belize sites of Cuello and Pulltrouser Swamp.

  Ancient texts describe several recipes, for ceremonial, medicinal and culinary use. Some mixtures included maize, chili, vanilla or honey. The Aztecs are also believed to have ground cacao and mixed it with tobacco for smoking.

  In Maya belief, the gods found kakaw inside a mountain that also held other delicious foods. The Plumed Serpent then gave it to the Maya, after the grandmother goddess Xmucane had created humans from maize. Each April the Maya honored their cacao god, Ek Chuah, with a festival. It included the sacrifice of a dog with cacao-colored markings, further animal sacrifices, offerings of cacao, feathers and incense, and an exchange of gifts.

  The Mexica told a parallel tale in which the god Quetzalcoatl found cacao in a mountain full of plant foods. The Madrid Codex shows priests lancing their earlobes and covering cacao with blood as an offering. Only men took the drink in ritual, because it was thought an intoxicating food unsuitable for women and children.

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• 6. Money and Moctezuma

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  At one point the Aztec empire collected a yearly tribute of 980 loads of cacao, called xiquipilli, alongside other goods. Each load held exactly 8,000 beans. Good beans had real buying power, since 80-100 of them could purchase a new cloth mantle. The currency was valuable enough to attract counterfeiters.

  In 1519, the Spanish met Moctezuma in the Aztec capital of Tenochtitlan and encountered the drink. Cortés and others noted the vast quantities the emperor consumed and how his attendants whipped it beforehand. Cacao beans traveled back to Spain at that time alongside other agricultural products. The beverage itself seems to have reached the Spanish court in 1544. Kekchi Maya nobles, brought across the Atlantic by Dominican friars, met Prince Philip.

  Within a century, chocolate had spread to France, England and elsewhere in Western Europe. To supply the demand, the French established cacao plantations in the Caribbean. Spain built its own in its Venezuelan and Philippine colonies. In the mid-seventeenth century, the Dutch Golden Age artist Albert Eckhout painted a wild cacao tree in Dutch Brazil.

  Pre-Hispanic cacao drinks have not vanished. In Oaxaca, a beverage called tejate is still made today.

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• 7. Plantations and Processors

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  In 2023, cocoa beans were grown on roughly 11,650,000 hectares worldwide. Large agroindustrial plantations exist, but most of the harvest comes from millions of farmers working small plots. A tree begins to bear when it is four or five years old. About 1,200 seeds, the contents of 40 pods, are needed to make 1 kg of cocoa paste.

  Chocolate makers traditionally recognize three cultivar groups, Forastero, Criollo and Trinitario. Criollo, the bean the Maya used, is the most prized, rare and expensive. It supplies only 10% of chocolate and is arguably less bitter and more aromatic than any rival. In November 2000, beans from Chuao received an appellation of origin under the name Cacao de Chuao.

  Forastero beans go into 80% of chocolate. The most common variety is Amelonado, while Arriba types such as Nacional appear less often. Forastero trees are significantly hardier and more resistant to disease than Criollo, which makes their beans cheaper.

  Major processors of cocoa beans include Hershey's, Nestlé and Mars. Making chocolate involves harvesting, fermenting the pulp, drying and then extraction. One finding suggests that roasting with superheated steam gives beans of the same quality as an oven in less time.

  World production in 2023 was 5.6 million tonnes. Ivory Coast supplied 42.5% of it, followed by Ghana at 11.7% and Indonesia at 11.5%. A tree native to the Americas now owes its largest harvests to West Africa, where its worst enemies also live.

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• 8. Guarding the Future

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  Sahlbergella singularis and Distantiella theobroma are cocoa mirids that plague West Africa, while Helopeltis species do the same in Southeast Asia. Bathycoelia thalassina is another West African pest. In Southeast Asia the cocoa pod borer, Conopomorpha cramerella, attacks the crop, and Carmenta theobromae does so in Central and South America.

  Fungi add frosty pod rot, caused by Moniliophthora roreri, and witches' broom, caused by Moniliophthora perniciosa. Ceratocystis cacaofunesta brings mal de machete. Oncobasidium theobromae brings vascular streak dieback, and Verticillium dahliae is also on the list. Phytophthora causes black pod, and Phytophthora megakarya is the worst form in West Africa. Cacao swollen shoot virus, mistletoe, rats, squirrels and woodpeckers complete the roll of enemies.

  Researchers have found tools to fight back. Mass spectrometry was used to analyze these parasitic organisms and guide how to remove each one, and the method proved quick, reproducible and accurate. A bacterium, Streptomyces camerooniansis, helps the tree. It speeds up seed germination, inhibits oomycetes, fungi and other bacteria, and prevents rot caused by Phytophthora megakarya.

  Breeding new varieties depends on genetic diversity, but cacao seeds are recalcitrant, so they cannot be kept in a conventional genebank. The diversity is held instead in field genebanks of living trees. Experts drew up A Global Strategy for the Conservation and Use of Cacao Genetic Resources, as the Foundation for a Sustainable Cocoa Economy, and producers and their clients adopted it. It seeks to describe cacao diversity better, make the collections more sustainable and useful, and ease access to information about them.

  Some natural areas of diversity lie inside national parks. A recent study combined genetic diversity with predicted climates and suggested that many of those protected areas will no longer suit cacao by 2050. The same study found that the area around Iquitos in Peru will stay suitable and holds considerable diversity, and it recommends protecting it. The International Cocoa Quarantine Centre is another project, aimed at combating disease and preserving diversity.

  The cacao genome is diploid, with 430 Mbp spread over 10 chromosome pairs. In September 2010, a team announced a draft sequence of the Matina1-6 genotype. A separate effort, the International Cocoa Genome Sequencing Consortium coordinated by CIRAD, published the sequence of a Criollo landrace from Belize in December 2010, with the paper version following in January 2011. It identified 28,798 protein-coding genes, compared with roughly 23,000 in the human genome. About 20% of the genome is transposable elements, a low share for a plant.

  Many genes code for flavonoids, aromatic terpenes, theobromine and other metabolites tied to flavor and quality. A relatively high proportion code for polyphenols, which make up to 8% of the dry weight of pods. The genome also resembles that of the hypothetical hexaploid ancestor of dicotyledonous plants. The proposed explanation is that the ancestor's 21 chromosomes underwent major fusions, leaving cacao with 10 pairs.

  The sequence opens the way to marker-assisted selection, especially for resistance to the fungal, oomycete and viral diseases that cause huge yield losses each year. Cacao is grown only within 20 degrees north and south of the equator. In 2017-18, with concerns rising about extreme heat, Mars, Incorporated and the University of California, Berkeley began using CRISPR to adjust cacao DNA for hardiness in hot climates.

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