Acetaldehyde in a cream ale

Brewing Processes
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I brewed a cream ale several months ago that tasted fine (if a little boring) all the way until after it was carbonated (CO2 in a keg). It was a 3-gallon batch made with Czech Pils, 2-row, flaked corn, flaked rice, Willamette hops, and US-05, plus Campden, Whirlfloc, and yeast nutrient. Everything seemed normal and easy-peasy during the mash and brew. I then quickly chilled the wort to the mid-60s, aerated, then pitched yeast and immediately moved the beer into a fridge managed with an Inkbird. I let it stay in the fermenter several weeks, partly to clear it up and partly because I was busy, and cold-crashed it for about five to seven days. I racked it into a purged keg with a closed transfer (per AHA method).

After a week of carbonation, I tasted it and it had a pronounced green apple odor and a cidery flavor. I have never had this happen in a beer I brewed before. With encouragement, I submitted it to a local comp to get feedback, and the judges agreed on the flaws. I left it in the keg while life went on with various distractions and it still has that flavor/odor, albeit a little lighter.

Going by Palmer, and because the taste/odor didn’t show up until very late in the process (or at least I didn’t detect it, and I taste along the way), I’m thinking it may have been oxidation of acetaldehyde.

I have had the same CO2 tank for several years (getting ready to swap it out soon), so I don’t think it’s contaminated CO2.

One brewer suggested the fermenter may have sucked in oxygen during the cold crash. I can see that, though my process has been the same for years now.

Maybe I overpitched? I used one packet of US-05 for 6 lbs grain. But then would the issues have shown up earlier?

Was there something about the ingredients? I never make cream ales - and I used Czech Pils by accident. Same question though - wouldn’t the flaws have shown up earlier?

The adjuncts (rice and corn) were at 8% each. I used 3/4 oz total hops.

These days most of my major errors are at the packaging stage - I’m still trying to successfully bottle from a keg - so I’m a little stumped by this and hoping it is a one-off. I’ve brewed beers I liked and beers I thought were meh, but it’s been well over a decade since I brewed anything that qualified as a dumper.

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Carbonation can have an effect on aroma - which influences taste. So, there could be acetaldehyde caused by the fermentation process.

The process you’re explaining seems solid, so my gut is telling me that US-05 may have not been the right yeast choice.

Since you have control over fermentation temperature, I recommend looking into using a lager or kolsch yeast strain.

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Or BRY97 instead of 05

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Acetaldehyde is due to either weak yeast or oxygen exposure after fermentation. If the beer fermented normally and tasted fine after fermentation, then it was the latter. Acetaldehyde does not come from overpitching or from the ingredients.

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Acetaldehyde is normal during fermentation, but it should be reabsorbed by healthy yeast before fermentation ends. I believe you gave it plenty of time.

Because the beer was fine early on, but developed green apple flavors later I believe you have O2 ingress during packaging or cold crash.

A cpl thoughts: did you purge the close xfer hoses? Did you cold crash under CO2 pressure?

Some wild yeasts and bacteria (like Acetobacter) can produce acetaldehyde or convert ethanol into acetaldehyde and eventually into acetic acid. If it progresses from green apple to vinegar you have an infection.

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I did not purge the closed transfer hoses - but I will moving forward. I didn’t cold crash under CO2 pressure. Sucking in oxygen during cold crashing is something another local brewer brought up - and he mentioned the bag-of-CO2 approach, which sounds doable. It could also be that what is not detectable (to me at least) in my go-to brews - best bitters and Belgians – showed up in this beer because its flavor profile is so light.

Thanks for the tip about the wild yeasts and bacteria. I did wonder if it was an infection, and I’ll monitor the beer for a while longer. For my current brew, I used a different fermenter and other peripherals, even airlocks, and I considered switching from StarSan to Iodophor just in case it would address bug tolerant issues that could have developed in my environment - and I will also use a different keg and fittings, etc. This could be the excuse I need to treat myself - I mean, have Santa treat me - to a small stainless fermenter. My fermenters look ok but I’ve had them over ten years.

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Flushing the liquid hose is as easy as connecting the hose to the fermenter drain valve, depressing the QD peg, and opening the valve allowing beer to fill and flush the line into a bucket. I drain about 4 oz ensuring to flush any air bubbles from the hose.

Cold crashing under CO2 pressure is also easy. Just set the regulator to the carbonation PSI of choice, and attach the QD to the keg gas in post while cold crashing. Instead of sucking air it’ll suck CO2 and carbonate the beer.

No extraneous equipment required.

Cheers!

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I’ve read that you can krausen beer with Acetaldehyde and get the yeast in the krausen beer to absorb the Acetaldehyde and remove the apple flavor.

I have never tried it.

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That works for diacetyl. Dunno about acetaldehyde. And I’ve never had an issue due to not purging hoses.

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Flushing the liquid hose does seem easy. Cold-crashing this way sounds as if I would be transferring fermented wort into the keg and then cold-crashing and carbonating at the same time. I had been cold-crashing in the fermenter to clear the beer before transfer into the keg, but I can see this working, particularly since I use floating dip tubes.

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Yeah, I have the most “open” transfer process allowed and have never tasted acetaldehyde outside a can of Bud. Maybe I’m immune to it at low levels??

But…I also have never “cold crashed” a beer. At least not how everyone understands cold-crashing. To the OP, I’d look hard at the possible O2 suck-back there first.

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Just another thought on how to think big (goal to remove 100% of O2 ingress) and act small (do the little things that add up to accomplish the goal).

Of course, 100% is probably a bridge too far for me but the old adage that every little bit counts can get me closer. (Incremental continuous improvements)

Besides, it’s soooo easy to do, why not.

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This is similar to what I thought when I read about flushing the lines–it’s part of continuous improvement. And it’s so easy to do. I had a big mental block initially around closed transfers, and I was surprised at how easy it was, and that the process is also less messy to boot, and the benefits were immediately obvious.

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Cold-crashing has been a habit for at least five years. I do it as an easy way to help clear the beer. But I am not wedded to it, and with floating dip tubes (and patience) it may be superfluous. I could try not doing it for one batch, or I could experiment with the CO2 bag idea, which doesn’t look too challenging.

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The question for me is, is it really an improvement? Or is it just because we want it to make a difference?

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If you believe reducing oxygen ingress improves your beer, the question could then be whether flushing the line reduces oxygen ingress by an amount significant to bother with, whether it is hard to do, and whether there are adverse side effects. For me the answer is maybe, no, and no. I have to say the first time I did a closed transfer into a purged keg I wondered, why am I introducing oxygen into a keg I just purged?

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Point taken. It may be because I want it to work. I don’t have a measurement to confirm one way or the other.

…but since it’s too easy not to, uses very little beer, and flushing the line certainly doesn’t hurt anything, I figured I’ll miss 100% of every shot I don’t take. So I do it.

A thimble full of air can ruin an Olympic size swimming pool full of beer. ~ Charlie Bamforth.

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As Drew and I have said many times in our presentations, do whatever process/ritual that you want to do. He lights incense before he brews, so…..

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This is what never added up to me about cold-crashing. I transfer my beer to a keg and let it cold condition for a week or two - and use a top draw. So, for me, I can’t see any benefit to cold-crashing, just more work. But, I will admit, saying, “I cold crashed my beer” does sound pretty cool.

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I don’t see cold-crashing as more work - three or four clicks on the Inkbird and on I go. But I am thinking that cold-conditioning in the keg would painlessly eliminate any chance of oxygen suckback (also a fun expression :slight_smile: ) because the beer would already be on gas when the temp goes down. So no additional solution needed. I think I started cold-crashing in the fermenter before I started kegging and before floating diptubes became available… it’s always good to reflect on habits and whether there is room to change them.

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