A while back I conducted a similar experiment
. I considered the resuls inconclusive and was disappointed. But I kept it posted b/c of the fairly informative introduduction.
When I heard about the BYO/BBR experiment on that I asked James if I can review the results and he let me. Given that you already posted the conclusion here there is no NDA breach on my side.
The BBR/BYO experiments were in line with what I observed. The flavor differences where minimal though I though that the underpitched beers had a less clean flavor/aroma. But there was not the widely anticipated increase in ester production. This may explain why there is not much consensus in the literature about the effect of pitching rate on ester production. Some authors say that you get more esters with a lower pitching rate while others state the opposite. I may very well depend on the yeast and other factors.
I also think that fermentation temps are a much bigger factor in ester production. I regularly perform the fast ferment test. This is a test designed to expose the wort fermentability by using a high pitching rate and fairly high fermentation temperature. Many of these tests have a fruity/vinous aroma and taste to them in addition to the high alcohol notes. Light beers in particular turn out quite fruity. And most of them use lager yeasts.
The cases where the FG of the underpitched beers was lower than the FG of the other beers were odd and are indeed counterintuitive. To make a valid conclusion one would have to redo the experiments and pay attention to that particular effect. Maybe there is something to this and it can sometimes be the case that less yeast leads to a higher attenuation. But to really understand what is going on you’ll also have to analyze the final beer for its compounds. That will tell you what is missing and what is not.
I like what the guys are doing there although I do disagree with the idea of splitting info between BBR and BYO. There are many self perpetuating myths out there which could use a closer look. I’m not saying that underpitching will not give you increased esters, I’m only saying that it may or may not.