First All Grain. Acetaldehyde?

Not sure if this should be in the yeast forum or here, let me know if I need to move it. About 2 months ago I brewed my first all grain.

I did a Nut Brown kit from Northern Brewer with dry Danstar Nottingham Ale Yeast. Haven't used dry yeast in a long time and just rehydrated them as per instruction on the packet, didn't do a starter. Hit all the numbers (OG 1.045, FG 1.011) and transferred to a secondary after 1 week. Usually don't use a secondary and leave in the primary 3-4 weeks and I'm not really sure why I did this time, I think just bored one day. After 3 weeks in the secondary I kegged, cooled, then carbonated for 2 weeks. First pour tasted like wet grass mixed with dirty socks and was undrinkable.

The only variant during my brewing process was not hitting 170 F right away during the sparge and having to drain, heat up the wort, and add back in.
I'm 90% sure it is acetaldehyde but I didn't know if my recirculation during the sparge or another factor would have added the off flavors? If it is acetaldehyde will it settle out even though it is already in a keg, cold, and carbonated? My understanding was that warmer temperatures were better.

Acetaldehyde is is a byproduct of yeast and/or fermentation and sparge method(s) or all-grain vs extract would have nothing to do with it. Are you sure it's acetaldehyde? The compound has a distinctive green apple aroma. Certain yeasts, in particular the Anheuser-Busch lager strain, are notorious producers.

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.

TonySwank said:

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.

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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.