Chocolate has long been a passion
of mine. So much so that my GCSE English speaking presentation was on the
subject. Sadly for me, but fortunately for you, dear reader, the content of
said work has long been lost somewhere in the unsalvageable hard drive of an
ancient computer, so cannot be easily regurgitated here. However, morsels still
remain in my memory and my alleged development as a scientific researcher may
help in producing something ever-so-slightly better than my 16 year-old self could
manage. Although I gave out actual chocolate samples in my presentation, so I
am not entirely sure about that…
I’ll start with a little bit of
botany, with a twist of geography for good measure. Chocolate is made using the
beans from the cocoa tree, Theobroma
cacao. This is indigenous to the Central and Southern American tropics and
is one of 22 species of Theobroma,
whose name means “food of the Gods.” You
will possibly have seen a specimen at the Botanical Gardens, or on your Gap
Yah, if you did such a thing. Recently, scientists have been using genetics in
order to track the spread of plant and its cultivation and domestication. They
have found 10 distinct genetic clusters, separated largely by geography.
Interestingly, the most genetic diversity is found in the Upper Amazon region,
indicating that this is where the species originated. However, the question of
when the tree was domesticated and cultivated for use is a contentious issue,
but vessels which could have been used for an early version of the fermented
cacao drink favoured by the Aztecs have been dated back to approximately 3500
years ago. However, this may not signify true domestication, rather
semi-cultivation. Some rather excellent scientists who use analytical chemistry
to analyse ancient pottery and have found that dry residue from Mokayan
(Mesoamerican settled villagers) pottery vessels contained theobromine, which
is a remarkable compound found in chocolate (see below) and a clear indicator
of its presence. These vessels were dated from around 1900BC, so it’s clear
that chocolate has been used in one form or another for a very long time.
The Spanish Conquest of South
America resulted in the spread of chocolate to Europe and beyond. Upon their
arrival, Cortez et al will have found
a very different form of chocolate to that which we are used to today. The Aztecs
tended to use their chocolate in drinks, in which the beans were ground, mixed
with maize and peppers and fermented, which must have been a strain on the
European palate. Having said that, many Europeans (Brits, I’m looking at us)
are known for a taste for alcohol so it might not have gone down too badly!
However, upon coming to Europe, chocolate was, although still used as a drink, more
often mixed with vanilla and sugar to make it more palatable. The production of
solid chocolate in Britain began in the 18th Century, and involves
more interesting science.
The production of chocolate
requires extreme precision. There are a number of processes the cocoa beans
must go through to be turned from brown, shrivelled, bitter droppings into
velvety smooth richness, each of which has a specific purpose. After they have
been harvested, the beans are fermented and dried, giving them their dark brown
colour. They are then roasted to intensify their flavour, before winnowing to
remove the edible nibs from their husk. These nibs are ground to form cocoa
liquor, or cocoa mass, which is processed further to give two separate
products: cocoa butter, used in chocolate, and cocoa presscake, which forms
cocoa powder. The cocoa butter is mixed with additional cocoa liquor to form
chocolate and has to undergo substantial processing to achieve the correct
consistency and flavour, which is where the science comes in. The chocolate
must first be conched, which is much like kneading and serves to effectively
emulsify the fats within the chocolate, meaning that the cocoa butter is evenly
distributed throughout. Furthermore, this process helps to develop flavour by
eliminating some unwanted chemicals, such as acetic and butyric acids. The
conching is done at a temperature specific to the chocolate being made
(49-82⁰C), with higher temperatures reserved for darker chocolate. A higher
temperature promotes the Maillard reaction, which results in a caramelised
flavour in many foods. Amino acids and sugars react to form many different
flavour compounds unique to the food undergoing the reaction.
After conching, the chocolate is
tempered, which is another temperature controlled-process. This is of
importance to the texture, rather than flavour, of the finished product. The
melted chocolate must be cooled to 28⁰C, heated again to a temperature specific
to the type of chocolate you are using (27-32⁰C). This is because chocolate
crystallises in six different forms, and only one of these gives the right
texture to give the smooth, shiny,
snappable product we (I) expect. This form is the beta form, or form V, and
consists of small crystals. All of the other forms give a crumbly, rough, dull
mess. Chocolate that isn’t “in temper”-as the pros call it- also suffers from
the phenomenon known as fat bloom, where the fats rise to the surface and cause
a streaky, mottled, dullness. A similar phenomenon occurs in my brain from
time-to-time, I’m sure.
The production of chocolate
clearly involves some fascinating scientific morsels, but there is also a lot
of great science to be found within the reason for its sheer excellence: its
exquisite taste. Chocolate is home to 600 volatile flavour compounds, which
contribute to its unique flavour. 25 of these were found to be at a high enough
concentration to be recognised by human olfactory receptors. These comprise of
some very odd compounds which one would not necessarily associate with the
flavour of chocolate, such as dimethyl trisulfide, which smells like cooked
cabbage and 2- and 3-methylbutanoic acids which both smell rather sweaty. Dr
Peter Schieberle, a researcher at Munich Technical University, found that
combining these 25 compounds produced an aroma which was able to be identified
by humans as chocolate! Fascinatingly, the interaction of just 4% of the
flavour compounds found in chocolate with the olfactory neurons is sufficient
to convince the human brain that it is smelling chocolate. Schieberle intends
to use his work to tweak the chocolate making process in order to improve its
flavour profile. I didn’t stumble across much about the other 575 flavour
compounds in my (extensive and laborious-ish) research, but I am guessing that
they all contribute to the unique tastes of different blends and brands.
Something to look into on a rainy day, perhaps?
The flavour compounds in
chocolate aren’t the only interesting ones it contains. I mentioned theobromine
above, which is a signature compound of chocolate. This is a xanthine alkaloid,
meaning that it belongs to the same chemical family as caffeine and is also a
metabolite of caffeine, which is broken down by the liver into theophylline,
theobromine and paraxanthine. Much like caffeine, it is a diuretic and a
vasodilator (widens blood vessels). The compound was discovered in 1841 by
Alexander Voskresensky and its vasodilatory properties mean that it has been
used to treat high blood pressure, as well as arteriosclerosis (clogged
arteries) and angina. So you read it here first- chocolate is good for you!
It’s also an aphrodisiac- wink wink- and a reason why dogs and cats shouldn’t
eat chocolate. They metabolise theobromine slowly, so the accumulation poisons
them. Not so great.
 |
| Theobromine |
There is so much more to explore
regarding chocolate and health, as well as the science behind all aspects of
this wonderful stuff, but I’ll let you have a break. I hope you have enjoyed my
bounteous knowledge on the subject. To those of you who have reached the bitter
end, I salute you. Hopefully now you will be chock full of fantastic facts with
which to bore all of the people who leave a bitter taste in your mouth. Until
next time… chocks away!
References:
Powis, T.G., et al, Antiquity, 2007, 81 (314) http://antiquity.ac.uk/projgall/powis/index.html,
Clement, C.R. et al, Diversity, 2010 2, 72-106; doi:10.3390/d2010072
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0003311
http://www.sfu.ca/geog351fall03/groups-webpages/gp8/prod/prod.html
http://www.icco.org/about-cocoa/processing-cocoa.html
http://www.scientificamerican.com/article/sensomics-chocolate-smell/
Dr Peter Schieberle presented his work at a meeting of the American Chemical Society: http://www.acs.org/content/acs/en/pressroom/newsreleases/2011/august/whats-really-in-that-luscious-chocolate-aroma.html
http://www.sfu.ca/geog351fall03/groups-webpages/gp8/prod/prod.html
http://www.icco.org/about-cocoa/processing-cocoa.html
http://www.scientificamerican.com/article/sensomics-chocolate-smell/
Dr Peter Schieberle presented his work at a meeting of the American Chemical Society: http://www.acs.org/content/acs/en/pressroom/newsreleases/2011/august/whats-really-in-that-luscious-chocolate-aroma.html
