[Carson B]

I have gotten what I believe to be acetaldehyde (green apples, cider) in every lager I've made. I've never gotten it in any other beer, nor had any off-flavors in any other beer I've ever made. I sanitize like crazy, have glycol-mediated temperature control, so on and so forth. I've read major causes of acetaldehyde are oxidation (I transfer everything under CO2; beer never touches oxygen until the glass), infection, and incomplete fermentation. I don't see any of those being my issue, especially considering I've never had those problems with other beers. I cannot for the life of me figure out why I'm getting acetaldehyde, so I've come here for help. Perhaps the biggest help in identifying the issue is that I only notice it once the beer is crashed, kegged, and carbonated. Here's the last recipe and some notes as an example:

46% - Pilsner
26% - Munich
25% - Vienna
03% - Victory

OG: 1.049
FG: 1.012

90-minute boil
20 IBUs total of Hallertau Mit. and Saaz at 60 minutes

Wyeast 2308 Munich Lager pitched at proper rate after starter

Fermented at 50 degrees for a week when activity stopped, then gradually raised to 67 for diacetyl rest.
Once final gravity was reached and no off-flavors detected (about two weeks), cold crashed to 35 gradually and then held there for another two weeks.
Kegged after cold crashing. Five weeks brew day to keg. Planned to continue to crash/lager in the keg with floating dip tube.

Any detectives out there who can spot what might be causing this? This is just one of about five lagers I've tried, some with different yeast, and they've all had acetaldehyde. I am at my wits end.

[majorvices]

Hmmmm .... have you tried a different yeast? Seems like you are doing everything right.

Edit: I see you have. How trusting are you of your Co2 source? I have tested Co2 with a DO meter before with unpleasant surprises.

[Carson B]

Thanks for your response. I get all my CO2 from the same home-brew shop, and have never had reason to doubt it, but also haven't checked it for any DO. I haven't had issues with it on other beers. When I cold crash, I hook up the fermenter to CO2 for some positive pressure to avoid suck-back. If there is any O2 in there, that would explain everything. Still not sure why I wouldn't notice it in other beers though. Good avenue to look into still

[majorvices]

Maybe try natural conditioning and see if the problem persists. If they aren't getting beverage grade co2 it could *possibly* be a problem.

[RC]

First thing that pops into my head is, are you sure it's not also in your other beers? Ales are generally more strongly flavored, and the subtle presence of off-flavors is easier to miss. Maybe it's just more noticeable in your lagers because they are more "delicate" (man I hate that word when describing lagers).

What is your brewing water? Is it RO or distilled? If so, do you only use this water for your lagers? That would point to zinc deficiency. The enzyme that converts acetaldehyde to ethanol needs zinc to function properly. Sometimes just adding zinc sulfate is the solution to mystery acetaldehyde.

All that said, if you are not tasting off-flavors before cold-crashing, and then you do taste them, then clearly something is happening after cold-crashing. And the only thing that makes sense is oxygen exposure. Do you purge your kegs first? Are you filling them all the way?

[Carson B]

First thing that pops into my head is, are you sure it's not also in your other beers? Ales are generally more strongly flavored, and the subtle presence of off-flavors is easier to miss. Maybe it's just more noticeable in your lagers because they are more "delicate" (man I hate that word when describing lagers).

What is your brewing water? Is it RO or distilled? If so, do you only use this water for your lagers? That would point to zinc deficiency. The enzyme that converts acetaldehyde to ethanol needs zinc to function properly. Sometimes just adding zinc sulfate is the solution to mystery acetaldehyde.

All that said, if you are not tasting off-flavors before cold-crashing, and then you do taste them, then clearly something is happening after cold-crashing. And the only thing that makes sense is oxygen exposure. Do you purge your kegs first? Are you filling them all the way?

All good things to consider.

(1) If it's in other beers, I truly do not notice. And it's so strong in lagers, to the point of making them undrinkable, that I'd be surprised if it is in other beers. I also have no clue what would be causing it during at least the actual brewing and fermentation process.

(2) The water is typically a 50/50 split between RO and my tap water, dechlorinated with a Campden tablet. I use Brunwater for water chemistry stuff. I use it for most other beers as well. I do not know what the Zinc content is, though. I will absolutely add some Zinc sulfate next time. Never heard of doing that - what kind of concentration are we talking? It's worth noting I do add Wyeast Nutrient in the boil, and I imagine that's pretty zinc-rich.

(3) I go to great lengths to prevent oxygen exposure. The keg is filled with Starsan solution, then I push it out with CO2, purging the whole keg. The beer is then transferred under closed CO2 system. Full keg. I then purge the headspace further just for safety. Habit I got in making a bunch of NEIPAs.

[Carson B]

Maybe try natural conditioning and see if the problem persists. If they aren't getting beverage grade co2 it could *possibly* be a problem.

I've got a 2.5-gallon keg crashing in the fridge that I think I will bottle. I've never bottled them before, so that's a good next step to see where the problem might be starting. Thanks

[denny]

Are you certain it's acetaldehyde?

[RC]

In light of the new info, I can't imagine your beer is deficient in zinc.

If you do try the zinc sulfate, the dosage is exceedingly small: 10-20 mg per 5 gal. This small an amount can be hard to measure on a typical homebrewing scale, but you can make a large solution with an amount that is easier to weigh. Definitely don't use more than this, though, as too much is toxic to yeast.

You mention that you pitch at the proper rate, but what rate are you using, and how do you make your starters for your lagers?

This one is a stumper. I have one or two other ideas as to a source of possible oxygen, but they would involve your other beers as well. If this really is just limited to your lagers, then what do you do different for your lagers vs. your other beers? That would point to the cause.

[Carson B]

In light of the new info, I can't imagine your beer is deficient in zinc.

If you do try the zinc sulfate, the dosage is exceedingly small: 10-20 mg per 5 gal. This small an amount can be hard to measure on a typical homebrewing scale, but you can make a large solution with an amount that is easier to weigh. Definitely don't use more than this, though, as too much is toxic to yeast.

You mention that you pitch at the proper rate, but what rate are you using, and how do you make your starters for your lagers?

This one is a stumper. I have one or two other ideas as to a source of possible oxygen, but they would involve your other beers as well. If this really is just limited to your lagers, then what do you do different for your lagers vs. your other beers? That would point to the cause.

I pitch lagers at a calculated 1.5 million cells/mL scaled for gravity. Typical DME starter on a stir plate. The only difference is the lower fermentation temperature and extended cold crash. Everything else is exactly the same. Truly a stumper

[Carson B]

Are you certain it's acetaldehyde?

Not certain from a chemical analysis standpoint, but it's certainly not coming from any of the ingredients, and the flavor/aroma descriptors fit acetaldehyde perfectly (green apple, cider, etc.).

[RC]

In light of the new info, I can't imagine your beer is deficient in zinc.

If you do try the zinc sulfate, the dosage is exceedingly small: 10-20 mg per 5 gal. This small an amount can be hard to measure on a typical homebrewing scale, but you can make a large solution with an amount that is easier to weigh. Definitely don't use more than this, though, as too much is toxic to yeast.

You mention that you pitch at the proper rate, but what rate are you using, and how do you make your starters for your lagers?

This one is a stumper. I have one or two other ideas as to a source of possible oxygen, but they would involve your other beers as well. If this really is just limited to your lagers, then what do you do different for your lagers vs. your other beers? That would point to the cause.

I pitch lagers at a calculated 1.5 million cells/mL scaled for gravity. Typical DME starter on a stir plate. The only difference is the lower fermentation temperature and extended cold crash. Everything else is exactly the same. Truly a stumper

Hmmm...what about that extended cold crash. It takes time for oxygen to wreak its havoc. If your CO2 has excess oxygen in it, then you are allowing it more time to damage your lagers vs your ales, therefore you might notice it only in your lagers, even though your ales are also being damaged (they're just not being given enough time to show the damage). I'm not suggesting you are doing anything wrong, because it doesn't sound like you are. But as majorvices said, it could be your CO2, and the oxygen damage is revealing itself only in your lagers because of that longer cold crash.

[BrewBama]

Here’s a chart I’ve had for a while for a reference between the various grades. Not sure which vendor this is from or if it’s a standard all vendors adhere to. I just get my CO2 from a welder supply shop because it’s convenient.  So far so good.

[majorvices]

Here’s a chart I’ve had for a while for a reference between the various grades. Not sure which vendor this is from or if it’s a standard all vendors adhere to. I just get my CO2 from a welder supply shop because it’s convenient.  So far so good.

I tested some tanks we got from Sexton on our DO meter on YH a couple years back. They weren't 99.5%  pure. I don't remember what the reading was but off-hand, but it was high. If they aren't filled properly the reading can be higher than expected and whose gonna know if you don't check 'em?

I still get my home tanks filled there and they seemed to fix the problem when I told them about it but who knows what is going on with these tanks.

[Carson B]

Thank you everyone, sincerely, for the replies. Sometimes I'm surprised at how willing people are to try to diagnose someone else's issues when that beer will never reach them anyways! haha! It seems the leader in the clubhouse is the extended cold crash with extended CO2 exposure. I have bottled half of the batch as suggested above, and the next lager I make I think I'll take it straight from fermenter to keg (when it is tasting totally fine) and skip the cold crash just to see what happens