A couple points I picked up on were that fact that ester production is related to O2 levels and pressure. A recent triple I did may have been less estery than I expected due to over oxygenation and/or not sealing the lid on the prmiary for the first week of fermentation.
I think there are two seperate things going on here.
- Initial oxygenation: This can have a big impact on ester production as it also influences yeast growth and acetyl coA use. It's hard to isolate any one variable, but from what I've seen/read under-aeration can possibly increase ester production. The Clayton Cone Q&A that Denny has linked to before talks about this.
- CO2 inhibition: During fermentation, pressure/CO2 presence can impact ester levels. An open fermentation allows CO2 to dissipate. Ron Jeffries from Jolly Pumpkin has said that this gives him a more complex ester profile. He also uses shallow (square tanks), so pressure is lower. I'm not sure if there have been any studies on homebrew-size batches and whether tank geometry still affects ester production at the smaller scale.