Fermentation-like incubation of cocoa seeds. Guidance of the fermentation process.
The following is a summary of the stated research mentioned above. The content summarized here, including the figures and tables, all belong to the researchers (unless otherwise indicated). The summary attempts to stay as close to the original paper as much as possible with some adjustments in regards to jargon, length, or to focus on bean to bar aspects.
Introduction
The global chocolate market, as of 2010, was worth roughly 80 billion US-Dollars (Fairtrade Commodity Briefing, 2011). Native to the Andean slopes of the Amazonian basin, the cacao tree is the lifeline behind this enormous industry.
Chocolate is made from the seed of the cacao tree, but often erroneously referred to as a “bean”. This seed is made up of the embryo (a tiny little stick like feature) surrounded by two large cotyledons (that we often refer to as the nib). These cotyledons either feeds the growing embryo if growing into a tree, or in our case, are ground up to make chocolate!
The cotyledons consist of 50% fat (which we call cocoa butter), 15% phenolic compounds (relating to catechin and epicatechin, AKA anitoxidants), 12% protein, and 7% carbohydrates (e.g. Kadow, Bohlmann, Phillips, & Lieberei, 2013).
During fermentation, the seeds are still surrounded by the pulp of the cacao fruit. It’s the fruit which is degraded by yeasts, lactic acid bacteria, acetic acid bacteria, and the heat resulting from this activity. This results in acidic cacao beans post fermentation due to the build of lactic and acetic acid from the bacteria.
The acids migrate into the cotyledons, and break down components within the seed. The acids break down the storage proteins into peptides and amino acids, and storage carbohydrates into reducing sugars. The phenolic compounds which offer up the high doses of antioxidants, are also what cause the unpleasant astringency in unfermented and unroasted cocoa seeds (Jinap, Jamilah, & Nazamid, 2005). During fermentation, these phenolic compounds undergo browning reactions, which reduces their astringency and gives cacao its more characteristic brown colour (Fig. 1).
The amounts of free amino acids, reducing sugars, phenolic compounds, and organic acids are all excellent quality descriptors of raw cocoa seeds. Table 1 offers a great overview of typical quantities of the aforementioned constituents.
Keep in mind, that it’s not the microorganisms themselves (bacteria etc.) that are necessary for the breakdown reactions mentioned above, but their metabolites (the lactic acid). The two key factors in regards to the quality of fermented cacao beans are: the heat and acidification.
The study subjected fresh cocoa seeds to incubations under controlled conditions that mimicked fermentation but in the absence of microorganisms.
Materials & Methods
Pod & Seed Preparation
The surface of the pods were sterilized to remove any yeasts and other microbes. The pods were opened under a clean bench, with the seeds transferred to sterilized glass bottles.
Incubation
The fruit covered seeds were divided into 3 trial types depending on the incubation medium which was added to them. The 3 incubation mediums included:
Type 1 - 150 mmol*L-1 acetic acid solution.
Type 2 - 10 mL*L-1 ethanol solution for the first two days, followed by 150 mmol*L-1 acetic acid solution.
Type 3 - 10 mL*L-1 ethanol solution containing pectinase for the first two days, followed by 150 mmol*L-1 acetic acid solution.
The seeds from each trial were incubated for 5 days. The incubation temperature started at 30°C on day 1, 35°C on day 2, 45°C on day 3, and 50°C on day 4 and 5. The temperature was controlled using a water bath.
For the first two days, all trials were fumigated with nitrogen to ensure anaerobic conditions. By day 3, the nitrogen steam was replaced by an airstream. All were passed through sterile filters.
Drying
The seeds were dried in an oven for 5 days at 35°C.
Results & Discussion
Chocolate Flavour Precursors
Table one shows reference of free amino acid levels in cocoa. Table two shows the results from this experiment, which fall in line with results from (Rohsius et al., 2006). Levels of free amino acids are higher in Type 1, which is likely due to stronger acidification (acetic acid for all 5 days of treatment).
Reducing sugars, which are often known to be limiting factors in chocolate flavour formation, were found to be above the references in Table 1 for all 3 treatments. This suggests that fermentation-like incubation has high chocolate flavour potential since it increases the amount of the limiting factor: reducing sugars.
Astringency
Astringency is mostly due to phenolic compounds. Raw cocoa with a low degree of fermentation will likely have a strong astringency. Astringency is the dry puckering sensation you get when you drink a dark red wine or over steeped black tea.
An interesting note, is that phenolic compounds seem to inhibit the Maillard reaction, which is crucial to flavour development (Totlani & Peterson, 2005).
All samples in this experiment (Table 2) contained levels of polyphenols within range of standard actual fermentation levels (Table 1). Therefore, this fermentation-like incubation without the microorganisms still results in favorable polyphenol levels. Not too astringent, and not high enough that it would impede with flavour development.
Acidity
The acidity is mostly due to the acetic acid and lactic acid formed during fermentation from bacteria. All 3 types of incubation (Table 2) were in range with the reference amounts (Table 1). Therefore, this experiment didn’t result in excessive acidification of the cocoa seeds.
Chocolate Prototype
A chocolate was made from the cacao used in the fermentation-like incubation experiment. It was described as overall pleasant-tasting, with typical chocolate flavour and cocoa bitterness, with a slight astringency and acidity (Kadow et al., unpublished data). The authors point out further analyses are necessary to prove the reliability of this result.
Heat Effect
There is a great deal of variation in regards to temperature development in traditional fermentations (Fig. 3). If temperatures are too low throughout the fermentation will result in low amounts of flavour precursors, and high amounts of non-oxidized phenolic compounds.
The authors concluded that controlled heat and acidity during fermentation-like incubation was key to producing high amounts of flavour precursors and lower residual amounts of phenolic compounds.
Keep in mind that the seed itself plays a crucial role in the way fermentation proceeds. For instance, the seed shell (AKA testa or “husk”) behaves like a barrier to the acids at the beginning of fermentation. They state that the influence from the testa cannot be eliminated by the fermentation-like incubation.
Fruit Pulp Degradation
The molecular composition of the slime layer underneath the fruit pulp was not known at the time of this publication. They state it remains elusive which enzymes enable its degradation.
Conclusions
The authors suggest that from the results achieved here, that fermentation-like incubation (without the bacteria) can result in high quality cacao. They also suggest this may permit standardization and more mechanization of cocoa fermentation.
