Acealdehyde

[kocken42]

So I put down a kits 'n bits IPA about a month ago, and it has been sitting in secondary for about 2 weeks.

Being very adventurous, I thought I would give it a sip to see how it tasted...

(Some background info: yesterday, at university we had a sensory evaluation class, and it was all about fortified wines, the first set of wines were sherry's)

To my disgust, the beer tasted similar to some of the sherry we tried in class...it was completely aldehydic and utterly foul...I could smell the bruised apples as soon as I poured it. The taste was similar.

The culprit you ask? A lid which wasn't screwed on tight.

It's sewerage now.

Edit: Forgive the typo in the title. ACETALDEHYDE

 

[manticle]

Acetylaldehyde fades with time.

Not sure how a loose lid will equate to acetylaldehyde.

Sherry flavours are often associated with oxidation but I would expect that to take longer.

First sentence is most important.

 

[manticle]

So do you blame racking as the oxidation cause or the loose lid? Exactly how loose was the lid? I don't study any of this so I won't argue with your academic learning. However I rack almost every brew and use glad wrap and loose lids for anything that isn't being aged for a year - acetylaldehyde has happened but is rare and possibly attributable to other causes.

I guess my main point was - maybe the apple will fade so don't tip it but if your education and experience suggests it's unsalvageable then no point wasting time over it.

not quite sure I understand the first sentence. Does it mean - acetylaldehyde is a precursor to ethanol production and if detected early and before all ethanol has been produced might be absent in the final product but acetylaldehyde produced after primary ferment due to oxidation of ethanol will remain permanently?

You post disappeared while I typed that making me look odd.

 

[kocken42]

Well after posting, I did some further research and some of my points while not incorrect, were not the only correct answer.

I did throw it out, because it displayed these symptoms last week, and I thought I would let it sit a 'little' longer to see if it would change, it did change but for the worse. The smells and tastes were significantly offensive, and I highly doubt it's ability to come back from it. It was not a 'green' character displayed by young beers.

From my understanding, acetaldehyde will always occur during fermentation, but the yeast convert it to ethanol. This conversion can be reversed by the effects of oxidation, which will turn ethanol back into acetaldehyde. If there is enough viable yeast left in the secondary fermenter, they can feasibly re-consume the acetaldehyde and turn it back into ethanol, but with no other food sources and a presence of alcohol, it would be difficult for them to fire up.

 

[manticle]

I've always associated acetylaldehyde with yeast stress. Limited reading put acetyl-adh as a product of ethanol rather than the other way round. If I remember tomorrow, I'll have a look at a few brewing texts to see what pops up in reference.

I've experienced acetylaldehyde in a couple of brews and noticed it fade with time but my experience is limited and not a scientific paper or peer reviewed journal so I'm happy to adjust my understanding of things given further information.

 

[felten]

acetaldehyde is the immediate precursor to ethanol like you said, not sure about just a loose lid leading to it though.

heres a cut from BSP

Acetaldehyde is of special interest because of its role as the immediate precursor of ethanol. It has an unpleasant `grassy' flavour and aroma. Acetaldehyde is formed during the early to mid stages of fermentation and there after it declines to a low level. In some circumstances, it can accumulate during fermentation in concentrations above the flavour threshold of 1020 ppm. The principal causes of high acetaldehyde concentrations in beer are the use of poor quality pitching yeast, excessive wort oxygenation, unduly high fermentation temperature and excessive pitching rates

There's a possibility of a spoilage organism creating it as well.

 

[kocken42]

Yes, the above is correct...but that form of acetaldehyde will almost always be reabsorbed and turned into ethanol.
The form I'm referring to is the one formed due to oxidation.

Here is a piece from Wine Science: Principles, Practice, Perception by Ron S. Jackson (2000)

"Another source of acetaldehyde in wine is the coupling of autooxidation of o-diphenols and ethanol."

It then goes on to further state that this form rarely reaches detectable levels because the acetaldehyde reacts with free sulphur dioxide (not present in large amounts in beer), or is consumed in the polymerization of anthocyanins and procyanidins (which is also not present in large amounts in beer).

In regards to the spoilage organism, it is referring to acetic acid bacteria, which has the ability to oxidize ethanol to acetic acid (which is generally a vinegar taste, but can have cidery, green apple characters.)

 

[hsb]

What was the fermentation temperature/yeast?

 

[kocken42]

Yeast was US-05, ferment and storage temp was 18 - 20 deg C.

 

[hsb]

Sounds OK, just curious as it sounds like your yeast was not a happy yeast. You sound like you are up on the chemistry. A loose lid shouldn't cause oxidation in and of itself but something turned a good brew bad.

 

[Fents]

i just got it in a keg of pale ale i had, funny cause it did die out over time but last night i tapped a new keg of the exact same beer and out of the exact same fermenter and its a cracker. no apples anywhere. i have put it down to the first keg not being cleaned to well.