Acetaldehyde - Apple Off-Flavours

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Fingar

Acetaldehyde - Apple Off-Flavours

Post by Fingar » Mon Apr 23, 2018 5:53 pm

Hi Folks,

I recently brewed a variation of Greg Hughes Harvest Pale Ale which I racked into a Corny, purged the air and left it for several weeks with a residual amount of CO2. I then force carbed the beer and was hugely disappointed at the levels of apple flavour, which I assume is acetaldehyde. I have experienced this before when I bottled a pale ale and put it down to impatience as it was still a 'green beer' and had not conditioned properly. Over time, this off-flavour in the bottle cleared completely. In the case of my recent kegged Harvest PA, the ale had been conditioning in the keg for several weeks - probably 5 or so - so I was surprised at the level of apple flavour and was prepared to throw it away as I put it down to an infection and not being 'green'. About a week or so later, the flavour had completely disappeared, leaving a very good beer; very glad that it did not become drain cleaner.

I'm relatively new to this kegging malarchy, having only kegged about 10 brews, but have never experienced acetaldehyde in this form of dispensing. Is my process of racking into the keg, purging the air, adding a bit of CO2, letting the beer condition for a few weeks, then force carbing a day or so before serving the best way of doing things? Would force carbing straight after racking into the corny eliminate acetaldehyde from the offset, or is all of this a red herring?

I suppose the real question is, why was aceteldehyde present after several weeks?

Cheers... Fingar

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Re: Acetaldehyde - Apple Off-Flavours

Post by Haydnexport » Mon Apr 23, 2018 6:05 pm

I'm far from an expert , but when in doing lagers i don't keg it until all off flavours are gone and its 'clean' tasting.

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Re: Acetaldehyde - Apple Off-Flavours

Post by gaunt_paul » Mon Apr 23, 2018 6:24 pm

I've similar experience, where acetaldehyde has taken longer to clear in a force carbed beer than in bottles or pressure barrel. I put this down to the yeast being less active in the force carbed beer. The extra fermentation activity involved in natural carbonation might be helping those beers to clear more quickly.

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Bazz
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Re: Acetaldehyde - Apple Off-Flavours

Post by Bazz » Tue Apr 24, 2018 2:55 pm

If memory serves me correctly acetaldehyde can form when the beer is mixed with oxygen, this can happen if there is excessive splashing when you keg the beer and i've had it happen a couple of times to me. What i do now is to purge the keg with CO2 before the beer goes in, CO2 is heavier than air anyway so will sink to the bottom and displace the air, then transfer with a length of tubing that reaches the bottom of the keg. The result is minimal splashing and no oxygen for the beer to mix with, since i started doing this i've had no problems.

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orlando
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Re: Acetaldehyde - Apple Off-Flavours

Post by orlando » Tue Apr 24, 2018 3:52 pm

A couple of possibilities spring to mind fermentation problems or oxidation. All beers experience acetaldehyde as it happens when converting glucose to ethanol. If the fermentation is vigorous and the yeast healthy it will clear it all up. So first thing to ask your self is how good was it? Was temperature optimal, was it taken offf the yeast too early? The other is oxidation. Transfer is often the culprit although leaving the beer uncarbed may have had an affect too. Try carbing straight after transfer and see if the problem goes away. If you can use CO2 closed transfers to keg that is a really good option too.
I am "The Little Red Brooster"

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Drinking: Southwold Again,

Up Next: John Barleycorn (Barley Wine)
Planning: Winter drinking Beer

Fingar

Re: Acetaldehyde - Apple Off-Flavours

Post by Fingar » Tue Apr 24, 2018 10:14 pm

Thanks for the replies folks.

I don't think splashing of the ale at the time of the racking was an issue as I am very careful to avoid this.

I fermented at room temperature as I had no room in the beer fridge - the room temperature was fine. I used US05 yeast and at the end of fermentation, the krausen seemed to hang around in big clumps, which did not look very promising. Could this be the issue or a symptom of something else that was going on?

I am now going to fully carb at the time of racking once the ale temperature has gone down to about 3 degs C to see if that helps. Hopefully it is just a one-off issue.

Cheers... Fingar

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Re: Acetaldehyde - Apple Off-Flavours

Post by orlando » Wed Apr 25, 2018 6:44 am

Fingar wrote:
Tue Apr 24, 2018 10:14 pm
, the krausen seemed to hang around in big clumps, which did not look very promising. Could this be the issue or a symptom of something else that was going on?
Only if you took the beer off the yeast before it had fully fermented out. remember that reaching a "predicted" FG is not the end point. Keep the beer at FG for up to 3 days to ensure the yeast finishes the job. Did you rehydrate the US05 before pitching?
I am "The Little Red Brooster"

Fermenting:
Conditioning:
Drinking: Southwold Again,

Up Next: John Barleycorn (Barley Wine)
Planning: Winter drinking Beer

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Re: Acetaldehyde - Apple Off-Flavours

Post by Bazz » Wed Apr 25, 2018 2:15 pm

Every time i have suffered from acetaldehyde in a beer it has been when i have used US05 as well, i don't know if this yeast is more susceptible to it than others but it was one of the reasons i stopped using it, could just be a coincidence though.

McMullan

Re: Acetaldehyde - Apple Off-Flavours

Post by McMullan » Wed Apr 25, 2018 5:27 pm

You fermented at room temperature. The fermenting wort was probably at least 3, 4 or 5*C higher during vigorous fermentation. Optimal for excessive acetaldehyde.

Fingar

Re: Acetaldehyde - Apple Off-Flavours

Post by Fingar » Wed Apr 25, 2018 5:45 pm

Thanks for the replies... again.

My usual brewing practice is brew on a Tuesday, and rack two weeks later - never had issues before other than my early days experience.

My first and previous experience of acetaldehyde was from a Muntons yeast - but I think that this was a result of impatience and not letting the ale sit on the yeast for long enough, in addition to sampling the beer too quickly.

Maybe I should just ensure that the brew fridge, which doubles as my keg fridge is clear of kegs and set to the required fermenting temperature. I have done plenty of 'at room temperature' brewing before with no issues. This could be just one of those things.

Cheer... Fingar

McMullan

Re: Acetaldehyde - Apple Off-Flavours

Post by McMullan » Wed Apr 25, 2018 6:12 pm

Once vigorous primary is done temperature control isn't so important. If you get short for space, swap out the FV in the fridge for a fresh one :wink:

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