Acetaldehyde developing in keg

[freek]

[SIZE=10pt]I have a problem that I have been chasing for over 9 months now. The beers I brew all taste normal through fermentation and to the point of moving kegs into the kegerator at which point it starts to develop the classic “green apple flavour”. The longer it stays in the kegerator the worse it gets.[/SIZE]

[SIZE=10pt]I am positive that it is Acetaldehyde as I have learnt to identify this through BJCP off flavour kits. [/SIZE]

[SIZE=10pt]I have taken many actions to stop this from happening and nothing seems to stop it. Here is a summary of the process:[/SIZE]

[SIZE=10pt]- Single infusion mash 40L batch size.[/SIZE]
[SIZE=10pt]- 90 min boil. Put the lid on to sterilise near the end of the boil.[/SIZE]
[SIZE=10pt]- Chill to about 30 deg by lifting whole kettle and submerging in swimming pool with lid on. Approx 2 hrs in pool.[/SIZE]
[SIZE=10pt]- Rack to stainless fermenter; Fermenter [/SIZE][SIZE=13.3333330154419px]sanitized[/SIZE][SIZE=10pt] as follows:[/SIZE]
[SIZE=10pt] * Approx 3 hr soak with sodium percarbonate.[/SIZE]
[SIZE=10pt] * Rinse well with fresh water.[/SIZE]
[SIZE=10pt] * Mist spray Morgan’s no rinse sanitizer diluted to correct proportions.[/SIZE]
[SIZE=10pt] * Three piece SS ball valve fully disassembled and [/SIZE][SIZE=13.3333330154419px]sanitized[/SIZE][SIZE=10pt] separately the same way.[/SIZE]
[SIZE=10pt]- Put in temp controlled fridge (approx 6 hrs) to get to pitching temp.[/SIZE]
[SIZE=10pt]- When temp stabilised at 16 deg C:[/SIZE]
[SIZE=10pt] * Oxygenate with pure oxygen- no stone just sterile hose approx 5 min.[/SIZE]
[SIZE=10pt] * Pitch [/SIZE][SIZE=13.3333330154419px]re-hydrated[/SIZE][SIZE=10pt] US05- 4 packs for 40L batch. [/SIZE]
[SIZE=10pt] * Yeast stored in fridge but removed approx 12 hrs earlier to get to room temp.[/SIZE]
[SIZE=10pt] * [/SIZE][SIZE=13.3333330154419px]Re-hydration[/SIZE][SIZE=10pt] in water boiled for 10 mins prior to cooling with alfoil lid and following manufacturers instructions.[/SIZE]
[SIZE=10pt]- Ferment at 16 deg C for 2 days.[/SIZE]
[SIZE=10pt]- Raise the temp by 1 deg every day up to 22 deg C[/SIZE]
[SIZE=10pt]- Keep in primary for 2 weeks with lid and seal.[/SIZE]
[SIZE=10pt]- Rack to kegs- purged and [/SIZE][SIZE=13.3333330154419px]sanitized[/SIZE][SIZE=10pt] with CO2.[/SIZE]
[SIZE=10pt]- Prime each keg with 50g table sugar to consume any oxygen.[/SIZE]
[SIZE=10pt] * Sugar dissolved in water and boiled for 10 min prior to adding to keg.[/SIZE]
[SIZE=10pt]- Leave in keg in cool basement for approx 4 weeks. [/SIZE]

[SIZE=10pt]When I move the keg into the kegerator it tastes good, but a little young nonetheless. But after another three weeks the green apple makes it almost undrinkable. Its frustrating because I seem to be more cautious than others people I know who continually brew faultless beers.[/SIZE]

[SIZE=10pt]Can anyone help me here?[/SIZE]

 

[manticle]

Sounds like you have oxidised the beer at some point in the cold side. Have you measured DO levels from your oxygenation?
How are you transferring?
Try an active starter in a glass or in the keg to see if that helps reduce the level.

I am assuming in the above that your diagnosis is correct and it is indeed acetaldehyde you're experiencing.

 

[coopsomulous]

I would guess that over oxygenation is you problem as well.

Personally, I also use pure oxygen, however I limit my time to one minute. I only brew 20L at a time but I would not think that a double batch requires another 4mins of pure oxygen

 

[freek]

I don't measure dissolved oxygen. I dont have a way to do this. I used to use a sintered stone for 2 min with 40L batch (1 min on 20L batches). I threw the sintered stone away when it was moldy concerned about contamination. I can be sure of sanitation on a hose but struggled with the stone. I figure less oxygen dissolves with a plain 6mm hose end than with sintered stone so hence doubled the time.

I transfer straight from the primary to the keg with an sanitized elbow compression fitting and copper pipe that reaches the bottom of the keg. I put this on top of the sugar solution I had boiled for priming. The keg is fully sanitized and purged. I run sanitizer and plain water through the lines as well, although last time I dismantled my ss perlick taps after running sanitizer though to find gunk sitting behind the forward sealing ball, so I cleaned all parts individually and then reassembled.

I am almost positive it is acetaldehyde as I have tasted it in doctored beers and had BJCP judges identify it as a fault in my beer. It gets worse over time.

 

[freek]

Manticle, just reading your post again, thanks for the tip about the starter. I might try it to rescue this batch. I suppose it would just be a moderate size starter dumped into the keg and left a few weeks? I am not sure how practical it is to try on one glass if that is what you meant?

Though I am more concerned about eliminating it in future batches. It has ruined at least the last four batches for me.

 

[manticle]

The starter is as much a test as a fix. There's a few flavours an active starter can mend (acetaldehyde, vdks, possibly some minimal dms from co2 production) but many it won't.

I have little experience with pure oxygen but alarm bells went off when you said you do it for 5 mins. Too little is no good and it's nigh impossible to saturate with shaking or pouring from height but if you're not measuring what you put in properly, you are running a risk of adding too much.

 

[manticle]

You've got 4 bad batches. How many of those were oxygenated this way and how many good ones done similarly?

 

[waggastew]

Looking at your schedule another area you may want to look at is yeast and ferment temp.

- 16degC is on the low end for 05 although you have tried to compensate by pitching alot of yeast. I used to use 05 at 18degC but found it threw nectarine type esters. I now ferment at 19degC and its ferments faster and cleaner. Lower is not always better and can put the yeast under stress resulting in off flavours like acetaldehyde. A difference of a few degrees can make a big difference to the flavour profile of a yeast.

- 4 packs is a basically a double pitch for a 40L batch of standard gravity beer (assuming packs are fresh). Way overpitching (you have to go pretty high) can pump out off flavours.

- As said above too much oxygen is problematic. Given your very high pitch rate and alot of O2 your yeast will be spending alot of time reproducing before they start chewing through the fermentables. That means you end up with even more yeast, a bigger lag time, and not a great environment for the yeast to ferment clean.

So my advice would be oxygenate at lower amounts, pitch 2 packs of rehydrated yeast (assuming the packs are relatively fresh) at 18degC and then let free rise to 19degC and leave it there for a good week. Feel free then to bump up to 21degC to finish it off.

 

[danestead]

Not specifically related to acetyldehyde as off the top of my head I am unsure of the common contributors but the things that you are doing in yoir process that stand out as different to me are:

You are double pitching yeast as said above.
Get another airstone. Without an airstone, barely any will be getting dissolved, itll just be getting bubbled out into the air. As for 20L vs 40L batches, my theory is that 1min of o2 through an airstone is sufficient and similar for both sizes of batch as I think the 40L batch will allow more o2 to be dissolved into solution rather than bubbling out into the air.
Is it essential you dissolve your sugar in water? When priming bottles, you just add the sugar straight.

 

[Hpal]

I know the said benefits of oxygenating, and I may move to it one day, but I just pour from a height and splash and sometimes stir, and haven't made a bad beer yet.

 

[///]

Yeast health is the main one, did not see any thing about yeast nutrient. Same for temp, a racing ferment will not help with any ester, and fluctuations stress the yeast.

Can I also ask why you are using 4 packets? Over pitching is as near bad as under pitching.

This article was ok, do not worry too much about the big words in the top part.

https://beersensoryscience.wordpress.com/2011/02/04/esters/

 

[Topher]

The real question is how the hell do you lift a 40l kettle of near boiling wort and put it in your pool!

Sorry for thread derail.

 

[Mardoo]

That's both a crapload of yeast as well as oxygen in your ferment. I both way over-pitched and over-oxygenated a dark mild and got acetaldehyde after bottling.

I'm 99% sure my management of the fermentation and bottling was fine. Your results certainly sound similar, but I'm no professional like ///.

 

[freek]

Thanks everyone for the replies.

I am pretty sure I read an article from whitelabs (which I can find now) that said over oxygenating is not a concern even with pure 02.
As for the double up on yeast, this is something I have introduced to the process in attempt to combat the problems I am having. The classic advice for this problem is to increase pitch rates, but I guess this should be within reason.

That being said I have made much better beers with 1 pack per 20L and no 02, so I might go back to that if it works for everyone else. Smaller batch sizes is probably a good call as well. I am thinking 10L until I get my **** sorted. I do bust my nuts lifting 50kg and ruin my head tipping it down the sink later.

Manticle, its been so long since I have brewed a good beer and changed a lot on the way. So I cant answer your question on what effect the 02 had. Can you please also give some guidance on how to do the active starter in the keg or glass? I have no idea what proportions of yeast to now add and whether to add more fermentables to the keg or glass.

Cheers

 

[manticle]

You can most definitely over oxygenate. The article probably suggested it was unlikely in an hb situation with most setups. Impossible with shaking, not with pure 02.

As for the starter - just make a starter with a packet of 05, 100 g dme and 1L of water or a grain wort of 1040. Don't worry about stirplates or shaking - you are not looking for growth, you just need healthy, active yeast. Pour a pint, add a bit* of the active starter when it shows activity ( co2 bubbles when held to light or krausen) and leave for a few days in tenp controlled environment. Taste and see if there's any improvement - if so, make another starter and dose the keg.

However - this is a fix for acetaldehyde left unabsorbed by fermenting yeast because the beer was separated from the yeast too early.
If your problem relates to overpitching and oxygen saturation leading to oxidation products, I am unsure that it will work.
If you're going to use pure o2, either measure do levels or follow a tried and true time/pressure level.

*bit is technical term for a dash.

 

[NickyJ]

This is a touch off topic but why does everyone ferment at the lower end for US-05? What's the difference between a 19 degree ferment and a 22 degree for that yeast?

 

[mudd]

Hey freek.
I've been having a similar problem on and off for a few years now. So I understand your frustration.
Can't say I've been as thorough as you describe.
I still suspect my issues could be yeast health related. And I've probably overpitched as well as under at different times.
My basic problem is I'm too busy (or too lazy) to run my problems to ground so far.
I have been told bacterial contamination can in some cases throw acetyl-aldehyde. This may explain why its getting worse with age.
BTW I'm persisting with liquid yeast and reculturing because I'm too stubborn (after all learning something along the way is why I love this hobby)

Let us know when you nail it.
Mudd

 

[schoey]

This is a touch off topic but why does everyone ferment at the lower end for US-05? What's the difference between a 19 degree ferment and a 22 degree for that yeast?

US-05 (as well as the liquid equivalents, all yeasts in fact) throw off more esters at higher temps. Some may like these but my best beers with these yeasts have been at 17 initially, then raised after about 80% attenuation to 20 to finish off.