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“The superiority of chocolate, both for health and nourishment, will soon give it the same preference over tea and coffee in America which it has in Spain” – Thomas Jefferson in a letter to John Adams in 1785.

“The emotion behind chocolate: serve up a rare and unexpected taste of emotion” – Pierre Marcolini*

The many quotes and sayings by people over the years and centuries about chocolate are a demonstration of the love there is for this food. With variations in sweetness and bitterness depending on the variety, it is highly popular in the form of bars, as coating or filling or as a (hot or cold) drink. You’d be forgiven to think that with its wide availability globally, its development and production into consumable goodness is easy-peasy. However, looking at the science of how chocolate starts its life, a different story unfolds.



The life of chocolate starts with the cocoa tree, a small native to the tropical region of the Americas, the Amazon basin. In order to get fruit from the cocoa tree, it needs to be pollinated. And this is where things get interesting because the tree is non-self-pollinating, and yet it is prolific in its fruits. The cocoa tree has been in ‘human hands’ for so incredibly long (thinking back to Mayan and Aztec civilizations and probably even beyond) that we don’t really know what the cocoa tree originally looked like and how the pollination occurred.

Focussing on the tropical Americas, cocoa trees are mostly managed by smallholders in plantations, but how they get pollinated remains a bit of a mystery. Bees don’t seem to be involved. It turns out the main players are tiny flies commonly referred to as midges. Traditionally, it is still assumed that there is one particular genus of midge that is responsible for cocoa pollination worldwide. However, it turns out this famous ‘chocolate midge’ does not exist. VUB professor Bram Vanschoenwinkel and his PhD student Mathil Vandromme** found out that cocoa flowers are in fact visited by many different midge species and it isn’t entirely clear either where they come from. The researchers found that bromeliads, plants native to the tropical Americas, may play a big role in the pollination of cocoa trees. Vandromme’s research has allowed her to formulate advice for the smallholders in Nicaragua where she conducted fieldwork at the end of last year. The bromeliads house many cocoa pollinators.

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More often than not though the plants are wrongly seen as parasites and removed from trees, in or along plantations. The first of the research on bromeliads was done in Nicaragua and looked at the larvae of suspected cocoa pollinators. Sixty-six percent of bromeliads were home to gnats, the possible cocoa pollinators, especially in those with larger tanks and located in canopy higher up rather than closer to the plantation ground. It has resulted in advising the smallholders to NOT cut away these bromeliads, as they may ensure better pollination, thereby assuring higher yields. The mystery of the pollination continues however. The cocoa tree makes life hard for itself and for its pollinators: why not attract bees? Why have flowers that drop off after 1 day of flowering? And why so many flowers to boot? Professor Bram Vanschoenwinkel reckons that the long history of cocoa pollination ensured that the trees and pollinators present today might be very different than the wild relatives that grew in the Amazon rainforest in the past. Human selection of favourable pods and trees has changed cocoa. It’s clear though that finding out more about pollination requires a closer look at insects. It is striking that more than 5,000 years after the first cocoa was harvested by humans, we still don’t know what the pollinators are and how we can increase their abundance.

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Cocoa bean fermentation

But pollination isn’t the only factor in obtaining high-quality chocolate. After harvesting the cocoa beans are fermented, a spontaneous on-farm process so a lot can go wrong. In the VUB’s research group of Industrial Microbiology and Food Biotechnology (IMDO), professors Luc De Vuyst and Stefan Weckx have been investigating cocoa bean fermentation for many years, with research (being) done in Africa, Latin America, and South East Asia. Depending on the region, cocoa bean fermentation is done in heaps, baskets, trays, platforms, or in boxes in a (three) tiered-set-up and with regular rotation. All in all, the process takes 4-6 days. In the beginning, yeasts grow because of the anaerobic environment (meaning, they don’t need oxygen to grow) due to the tightening of the cocoa pulp-bean mass. They consume sugars present in the viscous pulp that surrounds the beans and produce ethanol, which slightly increases the temperature of the cocoa pulp-bean mass. In parallel, the yeasts depolymerize the pulp pectin, producing so-called ‘sweatings’, allowing air access for bacterial growth. First, aerotolerant lactic acid bacteria take over the fermentation process, which consume the sugars and citrate in the pulp and produce lactic acid, acetic acid, and mannitol, followed by aerobic acetic acid bacteria, which oxidize the ethanol to produce acetic acid. This further increases the temperature of the cocoa pulp-bean mass.

During the fermentation process, changes also take place inside the beans: the ethanol, acetic acid and heat penetrate the beans and cause structural and pH changes. This causes the breakdown of cells inside the beans, allowing enzymes to get into contact with metabolites. This results in hundreds of flavour precursor molecules which, after drying for typically 4-10 days, make up the cocoa flavour. Roasting of the fermented dry cocoa beans and their further processing finally results in the typical chocolate flavour.

To get a high-quality end-product, it’s vital to maintain good agricultural and farming practices: the cocoa pods which harbour the sticky pulp and beans, must be ripe when harvested, and plantations must be well kept. After these steps the fermented dry beans are sold off to intermediaries and processed further into cocoa solids and cocoa butter by chocolate manufacturers and eventually made into the end products we know and love.

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As spontaneous cocoa bean fermentation processes can sometimes result in poorly fermented cocoa beans, IMDO is investigating the use of functional starter cultures to control and steer the fermentation process. The group is currently involved in an SBO project (as it is called) with funding from the FWO (Flemish Government Fund for Scientific Research). IMDO’s research also involves metagenomics: DNA is extracted from all microorganisms present during the fermentation process, sequenced using high-throughput sequencing methods, followed by data analysis using high-performance computing systems, which unravel in high detail the identity of the microorganisms that are present, as well as the gene contents. This can be linked to the microorganisms’ functionality, i.e. which enzymes can be produced by the microorganisms. In addition, the research group also looks at the RNA level to see which genes are actually expressed during the cocoa bean fermentation process. Metagenomics is also part of a VLIR-UOS TEAM project with the Escuela Politécnica Nacional (EPN) in Quito, Ecuador. The project is two-fold: studying fermentation processes in Ecuador to define which microorganisms are present, but also capacity-building of EPN researchers, to help them with general microbiology, DNA extraction protocols, metagenomics, bioinformatics, etc.


All in all, it’s quite a remarkable process, given the cocoa tree is a bit of a mystery when it comes to pollination, and how easily the spontaneous cocoa bean fermentation process can go wrong. All the more reason to appreciate chocolate that little bit more this Easter!



**The research is supported by VLIR-UOS and the Global Minds programme.