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The Chemistry of Coffee (specifically espresso)

November 18, 2011


To me, the process of preparing espresso is a highly scientific process; we want a machine that deliver stable temperature and pressure; we want to dose a precise amount of coffee and the coffee must be ground to a precise distribution of particle sizes. The process of preparing espresso must be both accurate and precise and must be repeatable; all these criteria are essentially experiments in science. So the next time when you go and prepare your espresso shot, treat it as a mini experiment. 



I came across an article a while ago and just recently goes back over it; the tittle of the article is " Espresso- A Three Step Preparation" written by a German professor by the name of Klaus Roth published in a German Chemistry Journal. The Link to this article is here: http://www.chemistryviews.org/details/ezine/694285/Espresso__A_ThreeStep_Preparation.html



The article which deals with a lot of background pertaining to the preparation of espresso goes into a lot of details; first the chemical composition of the coffee beans are assessed.  From looking at the data, there are some points which seem a little problematic for instance they suggest there are more caffeine in roasted versus green coffee bean? Then the author goes into the process of roasting and the chemistry that is going on during this process. A little bit about grinding is discussed but seem very detailed and accurate (for instance, they stressed the bimodal distribution of grind size is important to extraction process. The chemical and physical changes that happens during the extraction is also addressed. They also reported a very interesting experiment which look at the flow rate when coffee cake was inverted after being partially brewed which seem to suggest the interesting effect of grind migration during the brewing period which ultimately affect the flow rate. This experiment I think is quite critical and support the observation that good espresso grinders produce bimodal grind size distribution.



What I liked about the article is that the author beside going into the details about the espresso extraction process also correlate those process with the sensory experience of espresso which is ultimately the whole purpose of everything. Afterall, we might be able to quantify all the variables that happening in espresso making but it would be very hard to quantify our reactions (taste, aroma, appearance) to the perfect espresso. This ultimately sum up everything about espresso, it is a science yet also an art! 






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