#FEMSmicroBlog: How microbes produce the delicious flavour of chocolate


Among the many steps in the manufacturing of chocolate, microbial fermentation of the cocoa beans stands out as a crucial process. Unfermented cocoa beans are highly bitter and astringent, nothing like the well-known delicious chocolate flavour. For today’s World Chocolate Day, Rosane Freitas Schwan explains which microbes are responsible for cocoa fermentation and the challenges we face for controlled chocolate production in industrial settings. #MicrobiologyEvents


Yeast communities metabolising cocoa seeds

The origin of chocolate, as we know it, is the tree Theobroma cacao, its seeds and its surrounding pulp. As the first step in the chocolate-making process, microbes naturally ferment and degrade the pectinaceous pulp for five to seven days.

Cocoa pods of different hybrids.

The microbial fermentation process of cocoa beans successively involves a wide range of yeasts, lactic acid and acetic acid bacteria. The pulp is rich in citric acid but low in oxygen; conditions that favour the initial colonization by yeasts. They secrete pectinolytic enzymes and anaerobically ferment the pulp carbohydrates, producing ethanol.

The abundant diversity of yeasts involved in the cocoa fermentation process is a true testament to the complexity and richness of this process. Depending on the region, different yeasts are involved, such as Trichosporon spp. and Candida spp., Cryptococcus spp., Hanseniaspora spp. (and their anamorphs Kloeckera spp.), Kluyveromyces spp., Meyerozyma, Millerozyma, Pichia spp., Rhodotorula spp., Saccharomyces spp., Saccharomycopsis spp., Schizosaccharomyces spp., Torulaspora spp., and Wickerhamomyces spp.


Bacterial communities producing chocolate aromas

After 12 to 18 h, oxygen penetrates the beans, allowing lactic acid bacteria to appear. The dominance of Lactobacillus spp. has been widely reported for cocoa fermentation in Ghana, Brazil, Malaysia, Indonesia, Ivory Coast, the Dominican Republic, and Australia. L. fermentum, L. plantarum, Leuconostoc mesenteroides, and Lactococcus (Streptococcus) lactis are the most abundant species during the first 24 h of fermentation.

After the decline of the yeasts and lactic acid bacteria, the characteristic vinegar-like aroma of cocoa beans is created by acetic acid bacteria. They produce ethanol as well as lactic and acetic acid resulting in the temperature rising to 45-50 °C. The ethanol and organic acids diffuse into the bean seeds resulting in a pH drop. The low pH in combination with the increasing temperature cause the bean embryo to die.

Fermentation boxes for cocoa fermentation.

This step activates two acidic-pH-dependent peptidases producing chocolate flavour precursors and resulting in the typical chocolate colour, flavour, and aroma. Together, microbes associated with cocoa fermentation produce several volatile compounds, alcohols, esters, and ketones, such as acetoin. The alcohols 2-ethyl-1-hexanol, 2-heptanol, and 2-nonanol can contribute to sweet, fruity, and floral notes, while aldehydes contribute to almond/fruity aroma and flowery notes and pyrazines to chocolate-caramel flavours. The esters isoamyl acetate and ethyl acetate are considered sensory quality markers.

The combined actions of peptidases as well as the lactic and acetic acids produced can be used as an index to evaluate fermentation success and bean quality. The microbial products, both the fermentation metabolites and the heat, directly trigger the necessary biochemical changes in the bean that affect the quality of the resulting chocolate.


Challenges and opportunities for increasing cocoa production and flavour

Yet, the cocoa fermentation process itself urgently requires improvements to achieve industrialization. As the microbial ecology of cocoa fermentation has defied industrialized control and management, we need to better understand the physiology of the involved microorganisms to improve and standardize cocoa production.

Based on this knowledge, a synthetic microbial starter culture could be developed containing the principal microbes from the natural fermentation process. Initial experiments with such cultures showed promising results and are a first step towards producing high-quality chocolate consistently.

It is also crucial to exert better control over raw materials and cultivate the best cacao varieties. Current monocultures are highly vulnerable to fungal pathogens, significantly impacting product quality.

Lastly, in Brazil, cocoa plantations are spread in several areas; most of them now occupy cultivated land instead of forestry. These traditional areas are cultivating cocoa in consortia with other fruits, aiming to increase sustainability, strengthen forest protection and restore cocoa-producing regions.

Our research group is currently investigating cocoa fermentation and chocolate production in non-traditional growing areas in Brazil, such as the North of Minas Gerais, West of Bahia and of Rondônia. Using native and cocoa hybrids, we aim to develop a standardized microbial cocktail and bioreactor to better control cocoa fermentation.

This approach will allow us to consistently produce chocolate of high-quality flavour with a health benefit for consumers. It also assures to protect forests while using only organic fertilisers, thus having a lower environmental impact.

Ready to indulge in a sustainable version of this delicious fermentation treat? Happy World Chocolate Day!


About the author

Rosane Freitas Schwan is a full Professor at the Federal University of Lavras. She received a degree as an Agricultural Engineer from the Federal University of Espírito Santo, a master’s degree from UFV (Viçosa-MG), PhD from the University of Bath (UK) and a post-doctoral internship at the Massachusetts Institute of Technology, USA. She was a researcher at the Cocoa Research Center (CEPLAC) where she developed techniques for improving the quality of chocolate and a cocktail of microorganisms to accelerate the cocoa fermentation process. At UFLA, she investigates the fermentation of coffee, sugarcane, cocoa, cassava and other substrates to improve quality and develop new products and foods.


About this blog section

The section #MicrobiologyEvents for the #FEMSmicroBlog reports about events and meetings relevant to our network. These include world awareness days, FEMS-sponsored meetings or meetings of Member Societies and many more.

The #FEMSmicroBlog welcomes external bloggers, writers and SciComm enthusiasts. Get in touch if you want to share your idea for a blog entry with us!

Back to top

Leave a Reply

Your email address will not be published. Required fields are marked *

Share this news