Originally Posted by TonySwank
I'm not sure it's acetaldehyde, mostly because I've never tasted anything that I knew was acetaldehyde. Don't like apples so aside from green apple Jolly Ranchers I don't have a great idea of the flavor in my head. After trying it for the first time I basically searched this forum with the term "grassy" or "grass" and everything seems to point to acetaldehyde. Combined with the fact that I pulled it out of the primary after only a week that sounded like a likely culprit, but I still wanted to check. Never experienced this before so it threw me for a bit of a loop.
I would second your analysis. I have been doing all grain a long time and never had acetaldehyde issues until I started fermenting my ales at controlled temps. I was used to transferring more on a time schedule than anything else. I was going a week in the primary, a week in the secondary then bottling or kegging.
When I switched to refrigerated ferment, I was fermenting several degrees cooler than I was used to (but still pulling my beers off the yeast after a week in primary). Immediately, the grassy, green flavor/aroma came to the forefront (and popped me in a couple of contests too).
Then I found this forum. You'll find a lot of people here who advocate 3 to 4 week primaries or longer with no secondary unless you plan to bulk age or dry hop a beer.
I don't have final results to show yet. I have only brewed twice since stumbling upon the advice on long primaries. I have a saison that is coming up on a month in the primary. A porter that is at 3 weeks. I can only say that at my most recent sampling earlier this week, the acetealdehyde present in the IPA I have on tap is missing from these two beers.
I would look no further than process for your next beer. Leave it on the primary yeast no fewer than 3 weeks.