Acetaldehyde in my Lagers! Please help.

So I've tried my hand at a couple lagers now, after spending the first 3-4 years of my brewing career just getting the hang of things. I've read up a bunch on lager brewing and am really dying to make some really clean, crisp lagers. Say what you will, but I love a good american lager, not to mention the european varieties.

So far, one thing has been persistent - acetaldehyde. I pick this up as a grape kool-aid kinda flavor. Last year I made a classic american pilsner as well as a german pils that were not great - they both had the same issue. This year, after doing some more reading, I tried my hand at a premium american lager. Low gravity, the yeast should be able to do this, right? I brewed the following in December 2014:

4.75 lb 2-row
4.75 lb 6-row
2 lb flaked rice
1 oz halletauer at 90 and 40 minutes.

Mashed at 148 for 2 hours.

For yeast, I did a 2L starter of WLP840 (american lager) for 2 days. Crashed and decanted, and added another 2L of fresh wort. In addition I also pitched another vial of 840 on top of the 4L starter. Used pure O2 for 90 seconds and yeast nutrient for each starter step and in the boil.

Pitched my refrigerated yeast at about 48 degrees. Held there for 2 days, brought it up to 50, held for 5 days, at which point my gravity was sitting at about 1.015. Then I let it free rise to 62, held for several days, then started to decrease by 1 degree/12 hours, down to 38. Held at 38 for 3 days, racked to purged keg and lagered at 42 for about 4 months. Attenuated from 1.050 to 1.007. Had that classic lager aroma when it went into the keg.

With much anticipation, I tapped the keg last friday only to be severely dissapointed from the first whiff of this beer. The acetaltehyde, while quite a bit less than my previous attempts, was still there. Not a totally failed attempt - better than previous, but still not quite what I was wanting.

From what I understand, acetaltehyde is a byproduct of fermentation and is typically cleaned up by the yeast. Am I not giving enough time in primary? Anyone have any ideas to help? Is it the yeast strain? Probably my most successful attempt was a faux lager, with anchor steam yeast. I'm dying for some clean, crisp lawnmower beers this summer.....Am I overpitching?

Any help from you lager brewers would be greatly appreciated! In the meantime, I'll just have to drink some saisons instead.....could be worse!
Thanks!

MrMalty suggests you're slightly overpitching...but not by much if anything.

Try taking tasting samples every few days during primary, with the idea being to leave it in the 60's until the acetaldehyde goes away?

Edit: this article mentions your yeast strain as being particularly prone to generate acetaldehyde. It's possible your oxygen infusion isn't sending as much as you think?

Are you sure it's acetaldehyde?

The 'grape koolaid' flavor is what makes me thinks something else is going on.

Acetaldehyde is more of a 'cut green apple' aroma, with maybe a hint of pumpkin in it.

Since it's an intermediate compound in the formation of ethanol, it usually goes away on its own in a young beer.

It can also be from infection, but that doesn't seem to be the case here.

Is the grape kool aid flavor a 'fruity' flavor? More 'fruity' than tart and apple'y? Wierd questions, I know.

Grape kool-aid doesn't sound like acetaldehyde to me, either. You may want to try a German yeast, like the Weihenstephen strain or the German Bock strain. Also, send a beer into competition to see what (if anything) is wrong with it.

Agreed with previous posters on grape kool-aid not being a common descriptor for acetaldehyde. However, I would say you may want to leave the beer on the yeast a little longer. I'm trying to eyeball how long you were on the yeast cake prior to cold-crashing, and I see 7 days ferment at lager temps, "several days" at 62 F, and then cold crashing. I often leave lagers on the cake for many days at the "diacetyl rest" temperature for exactly the reason you're describing, to convert both diacetyl and acetaldehyde. I generally aim for 3 weeks on the yeast cake for most lagers. That may be overkill, but longer doesn't really hurt; shorter may.

Further, as aangel said, the American lager strains have a stronger tendency to acetaldehyde. I find WLP833 to be the cleanest strain in my fermentations, followed by W-34/70/WLP830/WY2124, so a different yeast may help, as suggested.

However, I have had acetaldehyde develop in the keg a couple of times. The two primary potential causes I found through Googling around were (1) acetobacter infection and (2) oxidation. If oxygen is present, ethanol can oxidize back into acetaldehyde. Two things you may also consider, if this is indeed an acetaldehyde issue.

Yooper said:

Are you sure it's acetaldehyde?

The 'grape koolaid' flavor is what makes me thinks something else is going on.

Acetaldehyde is more of a 'cut green apple' aroma, with maybe a hint of pumpkin in it.

Since it's an intermediate compound in the formation of ethanol, it usually goes away on its own in a young beer.

It can also be from infection, but that doesn't seem to be the case here.

Is the grape kool aid flavor a 'fruity' flavor? More 'fruity' than tart and apple'y? Wierd questions, I know.

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It's definitely fruity, more than tart. I've also tasted it in professional lagers as well.

So when you say green apple, you're talking unripe, correct? Not like granny smith?

FarmerTed said:

Grape kool-aid doesn't sound like acetaldehyde to me, either. You may want to try a German yeast, like the Weihenstephen strain or the German Bock strain. Also, send a beer into competition to see what (if anything) is wrong with it.

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I got the same flavor, but worse from wlp830. That lager was also called out for acetaldehyde. Regardless, it's in a competition in 2 weeks.

mkeckjr said:

Agreed with previous posters on grape kool-aid not being a common descriptor for acetaldehyde. However, I would say you may want to leave the beer on the yeast a little longer. I'm trying to eyeball how long you were on the yeastht cake prior to cold-crashing, and I see 7 days ferment at lager temps, "several days" at 62 F, and then cold crashing. I often leave lagers on the cake for many days at the "diacetyl rest" temperature for exactly the reason you're describing, to convert both diacetyl and acetaldehyde. I generally aim for 3 weeks on the yeast cake for most lagers. That may be overkill, but longer doesn't really hurt; shorter may.

Further, as aangel said, the American lager strains have a stronger tendency to acetaldehyde. I find WLP833 to be the cleanest strain in my fermentations, followed by W-34/70/WLP830/WY2124, so a different yeast may help, as suggested.

However, I have had acetaldehyde develop in the keg a couple of times. The two primary potential causes I found through Googling around were (1) acetobacter infection and (2) oxidation. If oxygen is present, ethanol can oxidize back into acetaldehyde. Two things you may also consider, if this is indeed an acetaldehyde issue.

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Interesting. It was on the cake for 7 days at lager temp, 7 days raising to d rest, maybe 3 days at 62, then about 2 weeks crashing per narziss. So about a month. It attenuated really well, so I thought that meant the yeast were happy. ...

I purge my kegs with co2 prior to transfer from my 7 gallon ss fermenteR, and am always trying to minimize 02. The acetobacter is troubling. I'll look into that, thanks.

I ran into acetaldehyde issues with the first few beers I did in my freezer. I eventually figured out that my fermentors weren't sealing completely air tight and the convection of the air in the freezer was the culprit. It was never an issue with my closet ferments because of the lack of air convection. Something to consider if it is indeed acetaldehyde.

tgmartin000 said:

Interesting. It was on the cake for 7 days at lager temp, 7 days raising to d rest, maybe 3 days at 62, then about 2 weeks crashing per narziss. So about a month. It attenuated really well, so I thought that meant the yeast were happy. ...

I purge my kegs with co2 prior to transfer from my 7 gallon ss fermenteR, and am always trying to minimize 02. The acetobacter is troubling. I'll look into that, thanks.

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Ok, what about pitching rate and pitching temperature? Are you pitching warm and then chilling, or pitching cold?

you leave the beer on the yeast cake during lagering?

Yooper said:

Ok, what about pitching rate and pitching temperature? Are you pitching warm and then chilling, or pitching cold?

you leave the beer on the yeast cake during lagering?

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I attempted to pitch at 2 million cells/mL. I think for this batch I probably pitched at about 48, maybe 50, and chilled immediately to 48. Held there for 2 days, then let it free rise to 50.

I've never tried pitching warm. Could I be fermenting too low? Maybe 52 next time? Could it be a malt derived sweetness?

SC_Ryan said:

I ran into acetaldehyde issues with the first few beers I did in my freezer. I eventually figured out that my fermentors weren't sealing completely air tight and the convection of the air in the freezer was the culprit. It was never an issue with my closet ferments because of the lack of air convection. Something to consider if it is indeed acetaldehyde.

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Interesting. If that were the case, wouldn't it affect all my beers? I use the ss brew bucket. ..seems really airtight - I have to Crack the lid when I transfer, otherwise the vacuum almost prevents or from draining.

Yooper said:

Ok, what about pitching rate and pitching temperature? Are you pitching warm and then chilling, or pitching cold?

you leave the beer on the yeast cake during lagering?

Click to expand...

I forgot to mention that no, I don't leave the beer on the yeast cake during lagering. Should I?

mkeckjr said:

Agreed with previous posters on grape kool-aid not being a common descriptor for acetaldehyde. However, I would say you may want to leave the beer on the yeast a little longer. I'm trying to eyeball how long you were on the yeast cake prior to cold-crashing, and I see 7 days ferment at lager temps, "several days" at 62 F, and then cold crashing. I often leave lagers on the cake for many days at the "diacetyl rest" temperature for exactly the reason you're describing, to convert both diacetyl and acetaldehyde. I generally aim for 3 weeks on the yeast cake for most lagers. That may be overkill, but longer doesn't really hurt; shorter may.

Further, as aangel said, the American lager strains have a stronger tendency to acetaldehyde. I find WLP833 to be the cleanest strain in my fermentations, followed by W-34/70/WLP830/WY2124, so a different yeast may help, as suggested.

However, I have had acetaldehyde develop in the keg a couple of times. The two primary potential causes I found through Googling around were (1) acetobacter infection and (2) oxidation. If oxygen is present, ethanol can oxidize back into acetaldehyde. Two things you may also consider, if this is indeed an acetaldehyde issue.

Click to expand...

I'm not sure this is correct. My understanding is that acetaldehyde would form in the presence of oxygen due to the yeast being able to undergo oxidative phosphorylation and not needing to convert acetaldehyde into ethanol to replenish NAD+.

I know humans can turn ethanol into acetaldehyde and I think it will eventually be metabolized into Acetyl-CoA but I'm not sure yeast have the same metabolic pathways to convert ethanol back.

Not disagreeing that oxidation can lead to acetaldehyde but I think your reasoning of why it formed may be incorrect.

aprichman said:

I'm not sure this is correct. My understanding is that acetaldehyde would form in the presence of oxygen due to the yeast being able to undergo oxidative phosphorylation and not needing to convert acetaldehyde into ethanol to replenish NAD+.

I know humans can turn ethanol into acetaldehyde and I think it will eventually be metabolized into Acetyl-CoA but I'm not sure yeast have the same metabolic pathways to convert ethanol back.

Not disagreeing that oxidation can lead to acetaldehyde but I think your reasoning of why it formed may be incorrect.

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I very well may be wrong. I am not a chemist by trade. Seeing your comment, I decided to try to go and look back up what I used found that convinced me that post-ferment oxidation may lead to acetaldehyde. I found the following link:

http://www.picobrewery.com/askarchive/acetaldehyde.html

This is what I saw that put the thought in my head. Not being much of a chemist I'm trying to unify what you're saying with this web post. I think what you're saying is that there is no way for yeast to metabolize ethanol into acetaldehyde in the presence of oxygen. That very well may be true. I believe what this post is saying is that in the presence of oxygen, ethanol will oxidize into 1 water and 1 acetaldehyde without needing the help of yeast. There is no reference accompanying this article, so I don't know how much it can be trusted, but I figured I'd toss it out there.

Someone who is an expert taster should taste the beer and provide you with feedback. 4 months lagering a 5% beer is rather excessive where 4 weeks probably would suffice. But i digress. A properly lagered beer, that has been conditioned a very long time, can develop a fruity character that is not ale like, but may have a berry-like character in a good sort of way. A beer with a lower gravity also oxidizes more quickly and its character changes over an extended time. If it was enclosed in a keg it should not be too much of a problem, but think about times when you have consumed beer from an older keg of from your favorite brewery. Did it taste like a fresh version?

i would cut your lager time down and try again. make certain the fermentation is 100 percent complete prior to lagering. It does seem to me like you are doing things correctly except for the 4 months of time.

The beer has been submitted to a local competition for evaluation.

Full disclosure - when I first tried the beer, I was kinda buzzed up from drinking some Mama's Yella PIls all afternoon, so my palate was probably not fresh. I tried another few pints of this beer last week, and it seems like the off flavors have diminished significantly. Maybe there was some yeast at the bottom of my keg in those first few pints?

SO maybe it's just palate fatigue I was experiencing. I'll post with an update from the comp, but in the meantime thanks for all the great info, guys!

Grape candy like flavors are often malt derived. I can't remember the name, but Mosher discusses it in Tasting Beer. At low levels it is perceived as malty, but in high concentrations, it tastes like grape candy (the candy industry uses it.)

I detect this compound from Munich malt mostly, but a very vigorous boil is also associated with it. George Fix said that if you boil long and hard enough everything tastes like a bock.

I'm just throwing that out there in case maybe that's the issue. Without tasting your beer, I can't tell whether this is acetaldehyde.

philosofool said:

Grape candy like flavors are often malt derived. I can't remember the name, but Mosher discusses it in Tasting Beer. At low levels it is perceived as malty, but in high concentrations, it tastes like grape candy (the candy industry uses it.)

I detect this compound from Munich malt mostly, but a very vigorous boil is also associated with it. George Fix said that if you boil long and hard enough everything tastes like a bock.

I'm just throwing that out there in case maybe that's the issue. Without tasting your beer, I can't tell whether this is acetaldehyde.

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Interesting call-out on the Munich malt. I also notice that anything I make with Munich malt in it has a candy-like sweet "tang" to it until it has spent at least 5 or 6 weeks in the bottle.