I'm a bit confused about this.
In my own experience, I'm no longer experiencing acetaldehyde flavours in my beer after improving my aeration methods and at the same time starting to use yeast nutrient.
In his IPA book, Mitch Steele says that the biggest cause by far of acetaldehyde comes from dying yeast cells from which acetaldehyde escapes. It's also stated that acetaldehyde production increases with yeast cell growth - so aeration will increase acetaldehyde production.
I only use a primary fermentor, and it is always used for two week fermentations.
So, my theory to explain why I'm experiencing less acetaldehyde is that because I aerate better and provide a better environment to the yeast with yeast nutrient, there are fewer yeast cells dying at the end of fermentation.
Does this sound plausible?
Since aeration promotes acetaldehyde production, I think this also means I should be careful when dry-hopping to introduce as little air as possible to the fermentor. Yes, it will be 'scrubbed' out by the yeast consuming it, but this also means the yeast are producing acetaldehyde. I wasn't worried about introducing air when dry hopping before - because the common concern is oxidation, but it seems to me we should also be concerned about acetaldehyde when dry hopping.
The questions then are:
- Does my explanation of experience less acetaldehyde seem plausible?
- Should we worry about acetaldehyde production when dry-hopping?