Ah, chocolate: almost everyone loves it, and it's going extinct rapidly (time to stockpile :)). However, you might not realize how much work goes into the bar that you eat, and that the quality of the chocolate has a lot more to do with fermentation than you think. Going from cacao to cocoa can take up to a month, and it all starts with the fruit shown below, which through the process of microbial degradation creates the flavors we love in our chocolate, bitter, slightly acidic, sometimes spicy, and aromatic. This fruit, when mature contains mainly glucose and fructose, stored in the disaccharide form of sucrose. The beans are inside the white pulp, which has a low pH (3-4) and is high in sugar, because of the presence of pectin, saccharides, and citric acid, which later act as metabolites for micro-organisms. Well, why ferment chocolate in the first place, you might ask? The fermentation of the fruit has several purposes:
We all love chocolate, right? (Well, at least I hope you do; if not, I don't know if I can be friends with you). But how does it get its flavor? As it turns out, producing chocolate starts with the cacao beans, which are originally in the form of a fleshy, sweet fruit. It is still a so-called spontaneous curing process, in which microbes from the air inhibit the beans and transform their flavor. At the first stage of fermentation, yeasts dominate the cocoa environment, with their depectinizing activity that transforms the pulp into a liquid from a gel form. Hanseniaspora opuntiae/uvarum is often present at the beginning, due to its low ethanol and heat tolerance, but it is later replaced by saccharomyces cerevisiae, which thrives in that environment. The initial yeast fermentation reduces the pulp viscosity and allows for air to get into the fermenting mass, which encourages the aerobic-respirating bacteria to develop. The most important job of these yeasts is to produce ethanol from carbohydrates, i.e alcohol fermentation, namely sucrose. This disaccharide is then converted through invertase hydrolysis mechanisms in the yeast metabolism into glucose and fructose, the latter of which isn’t broken down by yeast. The ethanol produced will partly diffuse into the cocoa bean cotyledons (the embryonic leaf of seed-bearing plants) and either be oxidized into acetic acid , consumed by aerobic yeasts or disappear through sweating or evaporation. This all is an exothermic process, and it raises the temperature of the cocoa mass to 35–40°C within 48 hours. Yeasts are critical to the final flavor of the chocolate, as they create some of the acidity in the final bar, while developing volatile compounds that determine how a bar tastes. These organisms also produce acid, which acts as a buffer against bacterial contamination. After 24-72 hours, the air in the fermentation pulp allows for the growth of aerobic enterobacteria, namely LAB (lactic acid bacteria) and AAB (acetic acid bacteria). Ironically, some papers have found that LAB isn't necessary for the development of chocolate flavors. Nevertheless, it is a crucial step in the fermentation process, as LAB controls bacterial growth, encouraging fermentation through the control of the environment and acidity level. Glucose that is still available after yeast growth is fermented into lactic acid, acetic acid, carbon dioxide and/or ethanol, similarly to fructose. Although LAB is most active at this stage, since temperature, acidity and ethanol concentrations increase later on, LAB eventually declines in population size. The third and final stage is aerobic fermentation, where acetobacter species oxidize the ethanol produced by the yeasts into acetic acid, and the lactic acid produced by the LAB into acetic acid and acetoin. Sometimes, mannitol is also formed, as shown by Figure 1, but it depends on the type of acetobacter and yeasts initially present, and the type of bean. As these bacteria also cause an exothermic reaction, the mass's temperature increases to 45–50°C and even higher, limiting micro-organism growth and killing off the cacao and the yeast. As the acetic acid concentration increases and the cotyledon pH lowers (from 6·3–7·0 to 4.0–5·5), internal membranes of the bean cotyledon compartments degrade, so that substrates and enzymes mix. This is a key step in the fermentation of the bean, as it allows the seed germ to die due to the low pH (see Figure 2), and for all of the proteins and phytonutrients within the bean to break down into their constituents. Important flavor precursors are produced through this bioconversion, such as reducing sugars, hydrophilic peptides and hydrophobic amino acids, which later encourages the Maillard reaction during conching (roasting). Many companies now use starter cultures designed to inoculate cocoa communities, as it jumpstarts the fermentation process for bulk quantities. Valhrona, the high-end French chocolate company, has even invented a new fermentation technique that sets their chocolate apart: they add the pulp of local fruits to the fermented cocoa mash. According to their website, “the natural yeast and sugars of the fruit pulp work just like the sugars from the natural cocoa pulp in the first fermentation, and kick off the alcohol and acetic fermentation once again.”
Cacao originally belongs to the Mesoamerican continent, and it formed an integral part of Pre-colombian society. It was offered as a form of currency, worship, and trade; used for religious sacrifice, medicine, and often it was consumed unsweetened, in the form of a drink called Cacahuatl in Nahuatl, the ancient language of the Aztecs. Atole was/is another popular drink, made from corn, cacao, sometimes a little piloncillo (Mexican brown sugar), vanilla and canela (cinnamon). However, when the Spanish conquistadores came in 1519, chocolate transformed into a sweetened good and a major form of commerce for the European society, combined with the sugarcane trade from slaves and indentured servants in the Caribbean. Although the Spaniards managed to keep chocolate secret for a hundred years, it was eventually introduced to the French when the daughter of Spanish King Philip III wed King Louis XIII in 1615. Chocolates thus began to show up prominently in European pastries and confectionary shops, and were prized for their exclusivity. Europeans thus began to colonize cacao-producing areas and install plantations, as a means of making a large profit. When diseases brought by the European explorers killed native Mesoamerican laborers, African slaves were imported to work on the plantations. Chocolate was originally reserved for the aristocratic, however, as it was so expensive; it became accessible to everyone in 1828, when Dutch chemist Coenraad Johannes van Houten invented the cocoa press. The machine could extract cocoa butter from the roasted cacao beans, leaving behind a dry mass that could be pulverized into a fine powder to mix with other liquids and ingredients, poured into molds and solidified into what we know today as chocolate. This is proof that fermentation is essential to our lives: something many of us consume every day undergoes a rigorous process of decomposition and chemical transformation, under the guidance of a certain microbial community. Think about that the next time you take a bite: how far that bean has traveled to get from the fruit to your bar.
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