What does the nose know?
Photo: Battlecreek Coffee Roasters
One of the most interesting things we notice about coffee, time and time again, is that most people (including babies!) enjoy the smell of it wether or not they drink it or have even tasted it.
In fact, some even love the smell of it and can’t stand the taste of it! How can it be that someone may love the smell of something and hate the taste of it at the same time? The short (and really long) answer is: chemistry
Roasted coffee has over 800 compounds that each provide some measure of influence on the overall smell and taste of coffee. Specifically it’s the organic compounds that easily evaporate at room temperature and even faster with heat that impart so much character into coffee’s aroma, these chemical buddies are the ones hitting your nose and sending the signal to your brain that coffee is about to go down.
Have you ever held a bunch of unroasted coffee beans? People in the coffee biz call these beans “greens” because they have a greenish color and look more like a lentil then they do a coffee bean. What’s interesting is that the smell of a green bean is pretty much nothing like that of roasted coffee; in fact greens can smell nothing like coffee at all.
So what happens between the green bean and it’s roasting that causes all the wonderful-ness? There’s a very familiar process that occurs in roasting, and l bet your familiar with it… it’s called the Malliard Reaction.
Yep, the same reaction that occurs with searing, browning, baking and roasting (mmmm, marshmallows) occurs in coffee. When the temperatures get high and caramelization starts to occur - all those amino acids and sugars start to boogie and at some point, things get browned. So when you are smelling coffee it’s a bit like smelling bread in the toaster or hot cookies in the oven.
But the roast isn’t just about chemical change it’s about extracting compounds from the beans, and how well a compound can be extracted depends on its solubility (it’s ability to dissolve). Broadly speaking, different atoms exert different forces on the electrons around them, sometimes causing a polar reaction. Polar molecules are more soluble in water and when added to water (itself a polar molecule) causes the brewing coffee to release mostly polar compounds - because those compounds dissolve so easily, it’s what we pick up the most often in the aroma. That’s the chemical process of why coffee smells so good. Big old fat smelly compounds running the smell show.
The Specialty Coffee Association of America and the World Coffee Research organization just updated the flavor wheel for the first time in 20 years.Specialty Coffee Association of America
Louise-Camille Maillard
The Chemical Compounds Behind the Aroma of Coffee Source: Compound Interest
So what are these smelly compounds and where do they come from?
Well a big one is a sulfur based compound called 2-furfurylthiol. Easier to spell than it is to pronounce. But guess what that compound smells like on its own? Roasted coffee, go figure. Coffee truly is a complex and nuanced thing. The other compounds that figure into the aroma contain a variety of smells that on their own would (to some or even most of us) smell pretty bad, like methanethiol “rotten cabbage,” and my favorite, “3-mercapto-3-methylbutyl formate” which on its own smells like “cat.” There are a host of other compounds that create the fruity, caramel and earthy scents we prize... like most naturally occurring processes it takes a mix of good and bad to yield the smell result we know and love as coffee.
The next time you read the tasting notes on a particular coffee keep in mind that people who are trained in this area of smell are pros at their craft- it might not smell like blueberry to you, but if you isolated all the compounds one of them just might smell like blueberry on it’s own.
Sources:
American Chemical Society. "Coffee's Aroma Kick-starts Genes In The Brain." ScienceDaily. ScienceDaily, 16 June 2008. https://www.sciencedaily.com/releases/2008/06/080616092116.htm
Compound Chem. “The Chemical Compounds Behind the Aroma of Coffee.” Compoundchem.com. Compound Interest, 17 February 2015. https://www.compoundchem.com/2015/02/17/coffee-aroma/
