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The Chemistry of Coffee

More likely than not, the coffee you drank this morning was just as delicious as ever. Looks are ever deceiving though; the brewing process may seem simple, but it actually requires a lot of thoughtful factors. So, what exactly is the science behind that so called "perfect" taste?

You bring the cup to the edge of your lips, take a slight sip, and… ah yes – the perfect cup of coffee. At least, that is what it seems like! When it comes down to it, coffee sure isn’t your average (cup of) joe.

So what exactly is the science behind the drink that college students know all too well? The first word that comes to mind would be, of course, caffeine. Many choose the drink due to the compound’s effectiveness as an energy booster. Coffee actually acts as an adenosine-receptor antagonist. Adenosine slows down neural activity and tends to make an individual sleepy; caffeine then works to block this action. (1) While caffeine is surely relied on for a bit of alertness, it actually only has a small effect on the taste. Instead, a different group of compounds that make up coffee is responsible for that notoriously bitter taste. Chlorogenic acids comprise about 8% of unroasted beans, and when roasted, the acids react to form certain products that allow for that sense of bitterness. Their byproducts, one of being phenylindanes, are even sharper and allow for that characteristic espresso taste. (1)

The primary influence in the acquisition of such a satisfying taste is what is known as the Maillard reaction. (2) This is a chemical reaction that occurs between amino acids and reducing sugars. “Starches break down into simple sugars, which turn brown and change their flavor” – allowing for the characteristic tint we’ve come to associate with coffee beans (2). The caramelization that occurs from the intense heat during this process changes the flavor; the longer the reaction goes on, the more complex the taste.

Speaking of complexity, the one thing people love most about coffee is its rich smell. The distinct aroma actually comes from the various molecules that comprise it, including vanillin (a vanilla scent), pyridine (an earthy scent), ethylpropanal (a spicy scent), and much more. (3) When roasted, these smells combine and give off the aroma that we all know and love. (4) Since the mouth only picks up on certain sensations, most of what we associate with the taste of coffee is actually due to our sense of smell. (3)

Photo by Crew on Unsplash

So why does coffee made at home taste so different from when a barista makes it at a café? It often comes down to the brewing of it. The compositions of one’s cup are the reasons why the taste varies from place to place. A factor that accounts for this is water composition, which ensures what proportions of compounds are extracted from the coffee beans. Water rich in magnesium allows for a better extraction of the flavors, while levels of sodium and bicarbonates often ruin the taste. (3) The level of influence the water has depends on the grinding process, timings, temperatures, and much more. Many baristas have managed to perfect these variables, which explains the wide range of tastes in otherwise identical conditions.  (3)

To further account for that perfect taste, one must get down to the nitty-gritty… literally. The fineness of coffee grinds happens to have a key role. If the beans are more fine-ground, the surface area is actually reduced. This allows the extraction of the compounds to occur faster, and for the bitter compounds to better get through to the drinker. (3) While the type of coffee plant and processing surely have an influence on the flavor, it really comes down to making the most of the roast.

One often forgets how science plays a part in everything we do, even what we eat and drink on a daily basis. So next time you are drinking that perfect cup of coffee in the morning, take a second to just thank the chemistry behind it – words cannot “expresso” how pivotal it is in our lives.

Photo by Nathan Dumlao on Unsplash


References & Footnotes:

(1) “Why Is Coffee Bitter? – The Chemistry of Coffee.” Compound Interest, 30 Jan. 2014, http://www.compoundchem.com/2014/01/30/why-is-coffee-bitter-the-chemistry-of-coffee/.

(2) Andrei, Mihai. “What Gives Coffee Its Distinctive Color and Flavor.” ZME Science, 14 Sept. 2017, 12:57 PM, http://www.zmescience.com/science/domestic-science/coffee-chemistry-maillard-reaction/.

(3) “The Science Behind That Perfect Morning Cup of Coffee.” Coffee Science, 23 Mar. 2018, http://www.coffeescience.org/science-behind-perfect-morning-cup-coffee/.

(4) Kassel, Matthew. “The Chemistry Behind Coffee Is Surprisingly Complex.” MyRecipes, 25 Jan. 2017, http://www.myrecipes.com/extracrispy/the-chemistry-behind-coffee-is-surprisingly-complex.

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