On days that call for something roasty, the hand goes to the darker bag. A little way into roasting, the kitchen smells stronger than it did at the start. Deeper means more fragrant fits what the kitchen seems to say.
This piece looks at whether the studies bear that out, through two trials.
Darker is not always more fragrant
Lean over the cup and the roasty smell rises with the steam. That aroma does not always grow as the roast goes deeper.
When a prefectural station roasted further at the same temperature, the compounds used as its marker for roasty aroma came out higher in the light roast. Depth alone does not decide the aroma. What decides it is the pairing of temperature and how far the roast went.
For one picking season, depth made no difference at all. The sources show that within this trial the aroma did not increase. Next come two results that seem to point the other way.
Two results that look reversed
Open another report and this time the roasty compounds rise as the temperature climbs. The two look opposed, but they are answering different questions.
Climb a peak from the east and then from the west, and the view is not the same. One trial held the temperature and varied the depth; the other held the depth and varied the temperature. At one temperature, roasting further meant less; at one depth, hotter meant more.
Quote either one alone and the conclusion turns upside down. The sources show that the questions need reading separately. Beyond this lies something that happens only at the dark end.