[flbrewer]

My beer smelled and tasted great a week into fermentation. Took a sample today (10 days) and noticed some acetaldehyde aroma. For whatever reason when the sample is chilled I don't get this. Is this normal during cleanup?
The beer was pitched low and kept at 65.

[morticaixavier]

it could be normal although at day 10 I would hope it would have been cleaned up by now. not getting it when chilled is normal because acetaldehyde has a boiling point around 68f so you'll notice it more when the beer is warmer.

it can develop with an acetobacter contamination in which case there isn't really anything to be done but chill the beer and drink it.

you can try krausening which is pitching a big batch of very active yeast and hopeing they will clean up the acetaldehyde but if it's contamination that won't really help.

you can try warming the beer up and seeing if it passes that way as well.

[HoosierBrew]

you can try warming the beer up and seeing if it passes that way as well.

+1.  I'd let it sit @ 70-75F for a week. I'd wager it's gone by then.

[dmtaylor]

I agree with the others that warming this up might get rid of any acetaldehyde.  However...

Are you positive that it is acetaldehyde, which is that artificial green apple flavor/aroma?  Is it possible you are simply detecting the pear-like ester?  Pear esters are very common.  Green apple, not so much.  You might not actually have a problem at all, unless it is very distracting.

[flbrewer]

Yeah I'm not sure if that's what I'm smelling. Maybe it's just the Perle hops in this recipe.

[toby]

I'm remembering Perle having more a spicy aroma.  The key to acetaldehyde for me is that it smells exactly like a sour green apple jolly rancher.  Apple or pear esters don't typically have that artificial sour note.

[flbrewer]

It's pretty strange. I don't smell it at all upon re-tasting a cooled down sample. I'm going to let it warm up (sample) and see if I smell it again. I don't believe I ever tasted anything off. In this case, could it ever be truly an off-flavor if it were a smell?

I've also picked up some green apple Jolly Ranchers, a pear, and a green apple to see if I'm actually smelling any of these things in the beer....for science.

[ynotbrusum]

Good idea - you are employing the best method to track it down.  I agree with Toby and Dave - acetaldehyde is distinct from the other esters and I typically detect it in aroma and flavor when it is present.  Pear is common for me with U.S.-05 and WLP-029 - at least that is what I detect frequently.  I once had US-05 throw off some clove when I fermented a cream ale at really low temperatures (like 48F), but it could have been a wild yeast in that batch that just outcompeted the US-05.