Reducing acetaldehyde

I've decided to start kegging my beer now. This last batch (English Pale Ale) was the second beer I've kegged and it's apparent after a week that it still has strong apple-y flavor to it. My question is- should I just leave it in the fridge for a while, or does it need to be unpressurized and warmed up in order to clean up the early off flavors?

there are 3 things you can do to reduce acetaldehyde. try not to over pitch the yeast, make sure you aerate enough before pitching, and keep the fermentation temps lower.

to clean it up in the fermenter you can use a warmer lagering/conditioning temp, don't rack off the yeast, rouse the yeast to suspend it, use a less flocculant yeast next time.

I used a dry Nottingham ale yeast (first time using dry yeast). All I did was rehydrate it, no starter. My areation is probably like most; I don't use anything fancy, just violently swirl it around in the carboy for a while. Never had a problem with that before. Ambient temperatures were around 67F. Fermentation started fast and visible signs lasted 4-5 days. I left it in primary for 10 days before racking it to secondary. Left in secondary for 2 weeks, before racking it to my keg. Unfortunately, I wasn't able to take a FG reading until after kegging it and the reading was skewed by the yeast slurry in the sample. I suppose it's possible it finished higher than expected.

There should still be some yeast left at the bottom of the keg- do you think it's enough to get going again? Do I need to prime it a little to rouse it?

Hmm.. that reminds me. Can a FG reading be taken after it's been kegged and force-carbonated? Can I allow the beer sample to sit out and go flat, then take a reading?

As TipsyDragon mentioned,

1. Ensure sufficient aeration
2. Not to overpitch. This is not really possible in a homebrew setting unless one does the extreme of pinching on a batch of yeast cake. Otherwise, most of the time we are in fact underpitching
3. condition for 2-3 days at higher temperature
4. ferment at the higher end of the yeast's functional temperature range. That would increase esters but also reduce acetaldehyde

As for SG readings, being flat or not doesn't make too much of a difference, at least for the simple instrument that we use in homebrew.

hairy said:

As for SG readings, being flat or not doesn't make too much of a difference, at least for the simple instrument that we use in homebrew.

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thats not true. the CO2 could cling to the hydrometer making it float more. not sure if it would actually affect the density of the sample.

You could do a starter of fresh wort and add that to the keg after a day or two. That would likely clean up any acetaldehyde assuming that is the problem. You have already racked the beer off the yeast twice now, and Nottingham is fairly floculent, so you probably don't have a large quantity of yeast in there, otherwise I'd suggest moving the keg from the fridge to the basement or somewhere around 65F.

Edit: Thought of something else... At what temperature did you ferment? Nottingham can generate some interesting flavors if it gets too warm.

uwjester said:

You could do a starter of fresh wort and add that to the keg after a day or two. That would likely clean up any acetaldehyde assuming that is the problem. You have already racked the beer off the yeast twice now, and Nottingham is fairly floculent, so you probably don't have a large quantity of yeast in there, otherwise I'd suggest moving the keg from the fridge to the basement or somewhere around 65F.

Edit: Thought of something else... At what temperature did you ferment? Nottingham can generate some interesting flavors if it gets too warm.

Click to expand...

No higher than 68F (ambient temperature). Also, my OG was 1053, FG was 1018. On the low end of the attenuation, but still within range of a sweeter ale. I think I"m going to wait it out for another week, then perhaps let it set in warmer temps (room temps) for a few weeks if it's still too "green".