Microorganisms, Chemistry and Chocolate: a Delicious Relationship

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Chocolate has been one of the most consumed products in the world for generations. European countries tend to top the list: in 2017, Switzerland was the largest cocoa consumer per capita, with an average of 8.8 kg consumed per person.

In 1995 France launched the initiative to celebrate International Chocolate Day every September 13. The date coincides with the birthday of Roald Dahl, author of Charlie and the Chocolate Factory.

Still, it so happens that Milton S. Hershey was also born that same day. This American confectioner and philanthropist was the founder of the chocolate company The Hershey Chocolate Company.

The Hershey Company, usually called just Hershey’s, was founded in 1894 and is the largest chocolatier in the United States. During World War II, the company played an essential role in the war, collaborating with the government to produce chocolate bars for the D ration.

The chocolate bars were well suited to the extreme temperatures soldiers could experience. A mixture of chocolate, sugar, powdered milk, oatmeal, and vitamins provided 600 calories per serving. It turned out to be an excellent survival food.

How to transform cocoa into chocolate

The raw material for chocolate production comes from the cocoa beans of the cacao tree, Theobroma cacao. Although there are many steps in chocolate production, the cocoa beans’ fermentation is a critical process in the formation of the characteristic chocolate flavor.

Cocoa pulp fermentation is a spontaneous process during which the natural microbiota present on farms can ferment the pulp surrounding the beans, where bacteria and yeast grow.

In this stage, the degradation of sugars and mucilages takes place and consists of three phases:

  • The first phase is dominated by anaerobic yeasts – which do not require oxygen to grow – and lasts from 24 to 36 hours. In this phase, there is low oxygen content and low pH (<4).
  • The second phase is dominated by lactic acid bacteria present initially but is activated between 48 and 96 hours.
  • The third phase is dominated by acetic acid bacteria when aeration increases. During this last phase, an exothermic reaction occurs (conversion of alcohol into acetic acid), responsible for increasing temperature (50 ⁰C or more).

In fermentation, the main bacteria that appear are lactic acid and acetic acid bacteria. In contrast, the diversity of fungi is wider. Generally, at the beginning of the process, there is a wide diversity of fast glucose fermentation species. Later, more robust and stress resistant species predominate.

Yeasts play several crucial roles in the fermentation of cocoa pulp. They degrade the thick pulp rich in pectin and, in the process, generate ethanol, organic acids, and volatile aromatic compounds.

Microorganisms facilitate the appearance of numerous chemical compounds that contribute to the taste and aroma of chocolate.

More than 600 different chemical compounds have been identified in chocolate. One of them is 3-methylbutane, which gives a malt aroma.

Different compounds for different chocolates

Among the common types of chocolate that we eat, dark chocolate has the highest percentage of cocoa (> 35%). It contains theobromine and phenylethylamine. The first is toxic for dogs: the intake of 300 milligrams of dark chocolate for every kilo of weight of the animal can be lethal. 

Even a dose of 80mg / kg is enough to cause severe intoxication. With 20mg / kg, mild signs such as polydipsia and polyuria (drinking and urinating a lot) and diarrhea may appear. On the other hand, phenylethylamine is linked to the pleasant effects that chocolate causes in our brain.

Milk chocolate has between 20% and 30% cocoa and usually contains vanillin, incorporated by producers to improve the flavor. Butyric acid is also added to some milk chocolates because it adds a characteristic bitter flavor to the chocolate. 

White chocolate contains no cocoa, only cocoa butter, sugar, and milk. Cocoa butter is composed mainly of stearic acid and palmitic acid along with other oleic acids. It has a unique melting behavior with a much narrower melting range than any other fat. This quality is essential for chocolate, which must be hard, even in hot climates, and must not stick to the fingers.

At room temperature, about 70% of the triacylglycerols in cocoa butter are solids. This range allows the chocolate to melt completely in the mouth and cause a pleasant sensation. Unfortunately, palmitic is a saturated fatty acid. There is an express recommendation to limit its consumption due to its potentially harmful effects on health.

The relatively narrow melting range of cocoa butter is essential in chocolate production. When the chocolate cools, and the fat solidifies, there is a considerable decrease in volume. This contraction facilitates the release of the chocolate from its molds. Thus, chemistry and microbiology allow us to taste this precious sweet.

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