Carl Linnaeus, the father of taxonomy, aptly named the cacao tree Theobroma cacao, which means ‘food of the Gods’ in Greek (Cook L. R., 2018). With its smooth, rich and creamy texture, eating a piece of chocolate is like experiencing heaven on earth. However, before we get to savour these mouth-watering treats, the cacao beans have to go through many harsh torments, which include roasting, husking, crushing and grounding. Most importantly, in order to turn those bitter seeds into the savoury antidepressants that we all love, the most crucial and very first stage in chocolate-making is the cacao bean fermentation. (Schwan R.F., et. al., 2004)
Once a cacao pod is ripe and ready to be harvested, it can hold up to 30-40 cacao seeds. Each cacao seed is encased in a white, mucilage-like coating, which contains water and approximately 10-15% sugars in it (Case C.L., 2011). The cacao seeds and pulps are microbiologically sterile until pod opening, which they are then immediately inoculated with a variety of microorganisms from the direct environment (Vuyst L.D., et. al., 2016). It is in this pectinaceous pulp where fermentation occurs. The high sugar content in the pulp, which is composed predominantly of glucose and fructose, provides an anaerobic environment that favours the growth of various microorganisms (Buczek M., 2017; International Cocoa Organization, 1998).
In general, there are a few microbial species involved in cacao fermentation. Among them are two bacterial species, which are the Lactobacillus fermentum and Acetobacter pasteurianus; and four yeast species, which are Saccharomyces cerevisiae, Hanseniaspora opuntiae, Hanguana thailandica, and Pichia kudriavzevii (Buczek M., 2017).
These microbes aid in the fermentation of the cacao seed as part of the ecological succession (Schwan R.F., et. al., 2004). The cacao sugars found within the white pectinaceous pulp that surrounds the seeds attract the Saccharomyces cerevisiae and other yeasts first (Buczek M., 2017). The growths of these yeasts ferment the sugars into ethanol in the anaerobic environment of the pulp (International Cocoa Organization, 1998). Ethanol production is an exothermic process and this causes a temperature increase from ambient temperatures of 25–30°C to 35–40°C within 48 hours (Vuyst L.D., et. al. 2016). As cacao fermentation progresses, the build-up of ethanol prevents further propagation of the yeast species and the yeasts species are slowly killed off by the ethanol they produce. (Buczek M., 2017)
Then, the fermentation process is taken over by the Lactobacillus species, a lactic acid bacteria (Buczek M., 2017). The glucose and fructose that is still present in the pulps after the yeast growth are now fermented into lactic acid, acetic acid, carbon dioxide and ethanol by the Lactobacillus species (Vuyst L.D., et. al. 2016). However, due to the exhaustion of energy sources and a still increasing concentration of ethanol and temperature, the Lactobacillus species numbers decline during later stages of the cocoa bean fermentation process (Vuyst L.D., et. al. 2016).
Due to aeration and pulp drainage, the presence of oxygen now favours the growth of the acetic acid bacteria, which is the Acetobacter species. The Acetobacter species oxidize the ethanol produced by the yeasts into acetic acid and acetoin; subsequently, the acetic acid is overoxidized into carbon dioxide and water (Case C. L., 2011; Vuyst L.D., et. al. 2016). In the continuing days, the ethanol, acetic acid and heat produced during cacao bean fermentation kills the cacao embryo (Vuyst L.D., et. al. 2016). The death of the seed causes cell walls to break down, thus allowing complex chemical changes, such as enzyme activity, oxidation and the breakdown of proteins into amino acids to take place. It is through these chemical reactions that cause the chocolate flavour and colour to develop. (International Cocoa Organization, 1998)
Thus, it can be said that a world without microbes is a world without chocolates. Microbial fermentation plays a very significant role in producing one of the earth’s most tantalizing treats. So the next time you subconsciously pop a piece of chocolate into your mouth or even crave for that cup of hot chocolate, just remember that chocolates aren’t just powdered seeds, but rather a delightful product of a complex micro-ecosystem.
Buczek M. (2017, March 30) Chocolate: the fermentation and flavours of the chocomicrobiome. American Society for Microbiology. Retrieved from: https://www.asm.org/index.php/general-science-blog/item/6289-chocolate-the-fermentation-and-flavors-of-the-chocomicrobiome
Case C. L. (2011) The microbiology of chocolate. Retrieved from: https://accounts.smccd.edu/case/chocolate.html
Cook L. R. (2018, Aug 9) Cacao. Encyclopedia Brittanica. Retrieved from: https://www.britannica.com/plant/cacao
International Cocoa Organization (1998, Aug 28) How does the fermentation process work on the cocoa bean and how long does it take? Retrieved from: https://www.icco.org/faq/59-fermentation-a-drying/132-how-does-the-fermentation-process-work-on-the-cocoa-bean-and-how-long-does-it-take.html
Schwan R.F., Wheals A.E. (2004) The microbiology of cocoa fermentation and its role in chocolate quality. Crit Rev Food Sci Nutr. 2004;44(4):205-21. Review. PubMed PMID: 15462126. Retrieved from: https://www.ncbi.nlm.nih.gov/pubmed/15462126
Vuyst L.D., Weckx S. (2016, Jan 7) The cocoa bean fermentation process: from ecosystem analysis to starter culture development. Retrieved from: https://onlinelibrary.wiley.com/doi/full/10.1111/jam.13045