Coffee chemistry (with a focus on popcorn)

Why does unflavored coffee taste and smell the way it does? What causes us to perceive notes like blueberry, honey, lemon, or tomato when we drink it? Now I'm no chemist, but I’ve always been fascinated by how our senses work in general, and so recently I started doing some reading. Specifically, I checked out a copy of Flament's "Coffee Flavor Chemistry.”

Coincidentally, not long afterward I was asked why it might be that for one person certain coffees inevitably smell like microwave popcorn. As a proof of concept, I’ll share what I managed to find out in that particular case.

Here's a list of some of the most well-known compounds perceived as popcorny (source; info. compiled by this prof):

popcorn: methyl pyrazine, propionylpyrrole, acetylpyridine, ethyldimethylpyrazine, acetylthiazoline

The first, methyl pyrazine, is classified as belonging to the "Grain" odor family, and the rest belong to the "Maillard" family, named after the Maillard reaction.

Some of these compounds occur naturally in roasted unflavored coffee. Under "Organoleptic characteristics of the most typical ingredients identified in roasted coffee" in the index of Flament’s tome* there's an entry for "popcorn" with references to many different compounds: 1 pyrrole, 3 pyridines, and at least 3 acetylpyrazines.

The acetylpyrazines especially seem interesting. They're described as a "class of particularly valuable natural products...with a surprisingly intense and characteristic roasted note reminiscent of popcorn (Roberts, 1968) (p. 324)." The chemist who originally isolated them worked for R.J. Reynolds, and apparently they're sometimes used to flavor cigarette tobacco. Odd, right?

Anyway, before too long I’ll probably circle back and look into some of the other perhaps more common tastes/odors that seem to crop up in cupping notes.

*Just as a teaser, here are a few highlights from this pages-long list: asparagus, bacon, bouillon, fishy, gooseberry, latex, myrrh, perspiration, seaweed, smoked meat, tree-moss, and wallflower.