What would be an advent calendar without chocolate? Christmas is invariably associated with this delicatessen, it is present everywhere around us. I am pretty sure we all already ate at least a tiny chocolate Santa. What I didn’t know, is that to have a good chocolate, you need good cocoa beans, but what controls the bean taste? Microorganisms! YAY! So here we go, day 10 of our Microbial Advent Calendar: The Microbiology of Chocolate! I found this review and let’s have a look.
Cacao was already used by human societies as food, beverage and medicine long before 1528, the year when Hernando Cortés brought it back to Europe and spread a new addiction. There are three main varieties of Cocoa trees: Criollo (not as cultivated anymore because it’s apparently susceptible to diseases), Forastero and a hybrid, Trinitario. Apparently another variety exists, the Arriba type, which is less cultivated and is considered as a fine type. The major producers are the Ivory Coast, Ghana, Indonesia, Brazil, Nigeria, Cameroon, Malaysia, and Ecuador (for the Arriba type). Other countries are also producing cacao on a smaller scale with more special types. For the past few years, the world production of Cacao has been around 4000 metric tones per year! (Here for some data)
Actually, to be more accurate, my original statement should not be that we will have a look at the Microbiology of Chocolate, but more precisely, the microbiology of cocoa bean fermentation. To have good cocoa beans is to have good chocolate, and the key processing steps in producing the most desirably flavoured cocoa beans are fermentation, drying and roasting.
Fermentation is the first step and should occur shortly after harvest. It often happens directly at the farm where it’s grown in a variety of forms depending on what is available to the farmer, smaller plantations will ferment the beans enclosed in banana or plantain leaves with some turning to assisted aeration. Baskets or boxes lined and covered with leaves are also used. In larger farms, fermentation is performed in large, perforated wooden boxes allowing the pulp which surrounds the beans to drain away and air to enter. The beans are covered with banana leaves or sacking to conserve the heat generated during fermentation.
Fermentation happens in several phases, where a succession of microorganisms will expose the cocoa beans to a variety of different compounds. Fermentation starts by a characteristic yeast colonization, they will consume the sugar and some of the citric acid present in the pulp surrounding the beans to produce ethanol, organic acids and a plethora of other metabolites. At the same time, lactic-acid bacteria will consume some of the glucose and other sugars present and will transform it into lactic and citric acids. At a later stage, the chemical composition of the environment will be modified and will allow acetic acid bacteria to persist. They transform the alcohol produced by the yeast into acetic acid. This succession of various acids and alcohols will fuel organic reactions within the cocoa beans and create metabolites which will define the bean’s taste.
Once the fermentation is done, the beans have to be dried slowly, generally sundried if the weather allows it (read here not stuck in rain season) if not they will be artificially dried in a gentle process over a few days. The drying should not be too fast as part of the chemical reactions started during the fermentation will slowly continue, otherwise off flavouring can happen and you will have bitter beans.
Beans are then processed further by being roasted for a couple of hours at 120-150°C, this step gets rid of most of the bacteria and other microorganisms present in the beans. The heat also induces a series of final chemical reactions that lead to the development of full chocolate flavour. You will then have beans ready to be processsed into chocolate Santas!