Ripping open a fresh bag of coffee and taking a good old whiff is a truly pleasurable thing (or at least it can be), but when freshly ground, it generally goes to another level. Hang around the grinder the next time your coffee is made if you don’t believe me. Unfortunately much of this lovely fragrance can dissipate rather quickly, but why?
There are many things that go into the complex aroma of coffee. While a large proponent is made up of sulfurous compounds including thiols (like furan-2-ylmethanethiol or the smell of roasted coffee) and even sweet, honey-like aromas, these compounds are highly susceptible to oxidation. Once ground, the carbon dioxide that was stored in the beans dissipates, and the surfaces of each particle of coffee come into contact with air. Oxidisation is unfortunately a bit of a bully, and picks on the smallest particles first. Often first to go are the sweet floral, and delicate spice notes. Some of the heavier compounds such as pyradines (smoky/ash), pyrazines (earthy/musty), and pyrroles (smoky/dark roast) as they are more stable.
Given this disparity in compounds, when cupping coffee it is often stipulated that the dry aroma should be sampled within no more than 15min of grinding the coffee. It is also common courtesy not to over agitate the coffee grounds. While agitating the grounds ensures you can experience more of the fragrance, shaking the cup madly to maximise the fragrance for yourself will also reduce the aroma experience for those following you. Thus, if you do agitate the grounds, do it gently by either cutting the grounds with your spoon to open up a fresh layer of coffee for you to sample, or tap gently on the side of the cup.
In summary, as the smaller, lighter particles are going to dissipate faster, don’t waste too much time before you stick your nose into the dry grounds. Have fun with the process, as everyone will experience the compounds differently (for many reasons that I will go into later). There is no wrong answer to the question “why do you smell”, so give it a go.
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