Thursday, 19 May 2011

Angel: The secret behind a good cup of coffee

The Cafe Terrace at Night by Van Gogh
Coffee makers are an indispensable piece of equipment in every lab around the world, whether you are doing research with toxic chemicals or just pencil and paper. Scientists and coffee have a special and close relationship, maybe because somehow coffee carries an intellectual meaning. Nowadays, there are many issues regarding the benefical or harmful effects it may have on the health of a coffee drinker. To highlight this, the RCS has recently published an interesting article related to the following question: is coffee a guilty pleasure or a life saving elixir? But, there are many aspects to keep in mind before this beverage developes the specific oganoleptic properties that reach your palate.

Espreso is closely defined in scientific literature as an extract of an aliquot (25 ml±2.5) of a coffee blend produced using water at 88°C±2°C over a 25±2.5 s period...

Every grain of coffee involves a complex mixture of over 1,500 chemical substances (chlorogenic acids, fatty acids, tocopherols and triglycerides) that undergo many chemical and physical process ranging from growth to the extraction process. Generally speaking, we can split these substances into two main groups: volatile and not volatile. There are around 850 volatile substances, to which the delightful aroma can be owed, while roughly 700 of these substances can be solubilized in water.

Coffee has always been there in the background, like a dark liquid melody, perfuming the air with the scent of lands far away and unlimited possibilities.

The flavor profile of each coffee bean is strongly related to the altitude, annual precipitation, atmospheric water vapour and diversity of the soil in each growing area. For example, at higher altitudes oxygen concentration and humidity decrease, consequently the kinetics of some biochemical reactions are affected; such as the cleavage catalysis of some lipids.

Coffee by Drooney (deviantART)

Another factor to be considered is the post harvesting practices like the storage time of green coffee beans before undergoing the roasting process. Flavour precursors such as sucrose, trigonelline, and chlorogenic acid can suffer chemical reactions, that have a strong influence on the coffee flavor due to time, temperature and humidity storage.

Nevertheless, maybe the most crutial step to guarantee a satisfactory quality (flavor, aroma and color) is based on coffee roasting. This complex process involves moisture loss and several chemical changes; as for example Maillard and Strecker reactions. Besides, a cooler proccess, using water or air as a cooling agent, is performed in order to prevent excessive roasting that would affect the quality of the product.

Coffee Physics by ~luke-b (deviantART)
Finally, the extraction process to transport all the remaining substances to your fancy mug is the last step for a succesful brew. Water is the biggest ingredient, so the final taste and quality is going to rely on its pH and mineral content. Another important factor is the flow rate and temperature of water that comes through the load of blended coffee grains. Acid substances are the first to be dissolved, so when faster flow rates are used, a sour coffee emerges. On the other hand, for low flow rates extra undesirable substances are dissolved and the sour flavor becomes stronger. To avoid these problems, for example, some brewers have a filter that controls the flow rate, standarzing and improving the end taste.

There are more other factors playing a key role behind a pleasant and fruity aromatic cup of coffe like harvesting methods, the storage of your precious coffee, brewing methods,  and an endless etcetera.  Fortunately, most of them have been studied by many scientists and we will try to develope each topic in this evocate series.


Tania Hershman said...

1500 chemical substances? oh my! Fascinating, thanks Angel!

CliftonCoffeeChris said...

Great article, Its really interesting to see some of the science behind coffee. Definitely makes it easier to explain why some coffee's taste better than others. We're always looking into ways the roast process affects the end product depending on how you're making it and what kinds of coffee you're using.