Chocolate Science

OK, be honest: how much chocolate did you eat this Easter? While it is common to enjoy masses of the food stuff at this particular time of year (along with Christmas), chocolate can well and truly be enjoyed at any time. Having said that, everyone will scoff their favourite (dark chocolate more than 70% pretty please) in larger amounts during Easter anyway so there is no better time than any to explain a little on the science of chocolate!

 

The cocoa beans in the pod. Picture from: http://www.bonamour.com/ingredients/theobroma-cacao-cocoa-seed-butter/
The cocoa beans in the pod. Picture from:
http://www.bonamour.com/ingredients/theobroma-cacao-cocoa-seed-butter/

 

 

 

 

 

 

 

 

 

 

Bitter Beginnings  

Family: Malvaceae

Subfamily: Byttnerioideae Burnett

Tribe: Theobromateae

Genus: Theobroma

Species: cacao

Chocolate is the final product from the processed and fermented beans of the flowering plant Theobroma cacao which is found in Central and Southern America. The trees are small, growing up to 15 metres in height with evergreen leaves and there are four varieties of cocoa, which is the powder that the bean yields; criollo, forastero, trinitario and nacional. Criollo was the first to be cultivated with domestication occurring about 3000 years ago in Central America. The first cocoa plantation was developed by the Mayans in the South Yucatan lowlands in 600 AD from which they concocted their drink chocolatl from the bean. While Chistopher Columbus (1451-1506) brought cocoa into Europe after 1502, it was not really introduced in Spain until Hernan Cortez (1485-1547) did so in the 1520’s. It reached Italy in 1606, France in 1657 and in the same year it reached France it was drunk in London for the first time.

 

Located in South America, the Andes Mountains are one of the longest and highest mountain ranges in the world stretching from the north to the south via the west coast of the continent by 4500 miles. It is thought that the creation of these mountains established the geographical barrier of the dispersal of lowland species. In turn this would have increased diversity in various animals and as Richardson et al (2015) state allowing the genus Theobroma to start diversifying. The divergence date of 12.7 million years ago from its sister genus Herrania supports this theory. The last common ancestor of all 26 species of T. cacao is dated to 9.9 million years ago and it is this early divergence time that has enabled it to accumulate a high level of genetic diversity (Richardson et al 2015). Argout et al (2011) identified that throughout the course of its evolution eleven chromosomal fusions reduced the number of chromosomes from 21 to 10.

 

Chemical Cravings

There are several challenges to the cultivation of T. cacao including plantation age, low density of trees per hectare, poor crop management and disease. It is because of this that Argout et al (2011) studied the genome and investigated how its genetics contribute to its quality and flavour, which is determined by the oils, proteins, starch, flavonoids, alkaloids and terpenoids. The storage lipids (fatty acids) provide the energy for germination and cocoa butter comes from it. It enhances the smell of chocolate and is used in cosmetic and pharmaceutical products. It is the high levels of stearate (C18H36O2) in this that gives chocolate its high melting point. Of terpenoids, which have a role in plant hormones, pigments and defence, two classes are involved in aroma. Flavonoids have a role in plant development as well and it is this component that studies on the health benefits of chocolate have focused upon. It is said to have benefits on the cardiovascular system, suppress inflammation and increase anti-oxidation. One of the main active components within chocolate is theobromine, which like caffeine but on a much smaller scale creates alertness and sharpens the mind. It causes the blood vessels to relax and has had some Viagra-like effects on men, which is probably where chocolate’s aphrodisiac reputation comes from!

But as with all foods, there is a dark side (and I don’t mean the chocolate that has less sugar and milk in it). Theobromine is a diuretic and can result in the same effects as caffeine overdose, such as headaches, anxiety and nausea. Whether dark or not, chocolate still has sugars and fat in it, which have been noted as significantly contributing to levels of obesity, diabetes and tooth decay.

 

From bean to bar

Have you ever tried eating a cocoa bean? I did many years ago in a tasting run by the chocolate shop Cocoa on Ecclesall Road, Sheffield. This is place is amazing!! But anyway, cocoa beans are really bitter and taste nothing like the final product.

The plants don’t start to yield fruit until their sixth or seventh year, but once harvested the fruit is cracked open revealing about 50 seeds surrounded by white pulp. Depending on the variety and end result, the beans and the pulp are removed and fermented for up to seven days. Because this pulp is packed so tightly preventing oxygen from getting in, the microbes that are everywhere on the harvester’s hands and knives start the process of fermentation: The yeast converts the sugars to ethanol and as they do so they produce enzymes that attack the pectin in the pulp turning it into a liquid which runs off. Eventually the process slows down as ethanol is produced and more air enters into the mixture. Acetic acid bacteria then convert the ethanol to acetic acid which further heats up the mixture to between 45-50 degrees Celsius leading to the death of the yeast and bacteria. The different types of microbes that contribute to bean fermentation can actually be quite different between regions. While there are some common species, certain differences can yield differing quality and quantity of cocoa. Identifying each species, their optimum conditions and the final result is actually what some teams are trying to do. By testing various culture mixes, fermentation can then be highly controlled because it is at this time when the components that affect flavour start to develop. For instance, the sugars, acids and amino acids like valine and glycine give the flavour while the proteins and peptides react with polyphenols to give the brown colour.

 

After fermentation the beans are then dried, usually in the sun. Storage and transport poses a problem for the beans in retaining their moisture. The moisture content has to be more than 6% otherwise cocoa becomes hard to process, but it must not be more than 8% otherwise the beans will become mouldy as they are shipped. Individuality and tailoring the taste becomes more significant in the Maillard reaction which is basically roasting or baking for flavour and colour. The beans are then cracked open revealing the usable part (the nib) in a process called winnowing and then the nib is further broken down reducing it to smaller particles in the particle reduction process. The smaller the particle can be broken down into, the smoother the chocolate is (yum!) The next step is conching: pouring the cocoa into a shell like apparatus and agitating it to spread out the cocoa, sugar and cocoa butter evenly. This lowers the viscosity making it easier to mould, evaporates volatile acids further changing the flavour. Finally tempering is repeatedly heating and cooling the cocoa to generate a type of stable cocoa butter crystal. It is ideal to have stable crystals as this ensures that the cocoa butter is tightly packed with a high melting temperature. This is what ensures shiny and smooth chocolate that melts in the mouth. After this the chocolate can then be moulded according to the manufacturer’s preference.

 

Have I just made you crave chocolate? Apologies! But the next time you find yourself digging your teeth into it, just remember and appreciate the hard science that went into making it; the evolution, genetics, chemical compounds and production. If you want to appreciate it even more, there are plenty of places around the UK that offer tastings and workshops. But as with all things, enjoy it moderation folks!

 

For more information:

Beckett, S.T. 2008. The Science of Chocolate. Royal Society of Chemistry Publishing, London.

Sheffield Cocoa: http://www.cocoawonderland.co.uk/

York’s Chocolate Story: https://www.yorkschocolatestory.com/

The Best Chocolate Shops in London: http://www.standard.co.uk/lifestyle/foodanddrink/londons-10-best-chocolate-shops-10149858.html

 

 

 

Danae Dodge

I received my PhD in Scientific Archaeology from the University of Sheffield in 2011 which specialised in ancient DNA and anthropology. For my profile, see my websites: http://independent.academia.edu/DanaeDodge https://www.linkedin.com/pub/danae-dodge/9b/868/389 I started getting involved in Science Brainwaves as a volunteer in 2010. I have volunteered at presentations, events (such as the British Science Festival in 2011) and even participated in the Science is Vital protest march in October 2010. My first blog for Science Brainwaves was "Ancient Humans: Who were they? And who got it on?" which was the written version of a talk I gave for the Natural History Society at the University of Sheffield on 5 December 2011. I also have a public engagement page dedicated to ancient DNA, which I encourage both the public and specialists to join: https://plus.google.com/communities/115424956261446503473