Recurring acetaldehyde problem with extract NEIPA brewed with S-04

[bw7hb]

Side not about eliminating your dryhop. instead of cutting it out completely, you could put them in on the 3 day of fermentation. That way the yeast will consume any of the oxygen that wort and force out any oxygen in the headspace. Just a thought. Good luck. I use to have the same problem but after getting some solid advise from Justin from Sloop Brewing Co and upgrading to kegging, I haven’t encountered it again.

Ok I think I'm going to do a half batch with just the pale ale extract, with a whole pack of yeast, and dry hopping once early on in fermentation. Then the test batch should still be fairly nice if it works

I've come across a method of dry hopping where you boil hops in plain water for about 10 minutes and add the liquid to your fermenter just before pitching yeast. Maybe that's a good option to avoid oxidization? Anyone have any experience with this method?

 

[Dgallo]

Ok I think I'm going to do a half batch with just the pale ale extract, with a whole pack of yeast, and dry hopping once early on in fermentation. Then the test batch should still be fairly nice if it works

I've come across a method of dry hopping where you boil hops in plain water for about 10 minutes and add the liquid to your fermenter just before pitching yeast. Maybe that's a good option to avoid oxidization? Anyone have any experience with this method?

That would be considered making a hop tea not deyhopping. Boiling it will cause you to isomerize your alphas and gain Ibus. Also you will boil off a portion of those precious oils you wanted to get into your beer by choosing to dryhop in the first place. Will it remove most of oxygen if not all? Sure, but if you really want to try something like that, you’d be better off boiling less than a cup of water to remove the dissolved oxygen. Then let it cool with out agitating so you don’t reabsorb Oxygen and the add the hops when your below 140 and let them break up without stirring(same reason, to not add oxygen) and then add to your beer without splashing.

All that being said id advise against it. I would just dryhop at the tail end of fermentation so that the yeast and co2 produced by the fermentation take care of the oxygen contact issue for you. Simpler for you and limits the potential for actually adding more oxygen if you’re not extremely careful.

 

[IslandLizard]

That!^
Yeah, forget about making hop teas, it's nothing like dry hopping nor an alternative.

Now, many of us homebrewers dry hop successfully after fermentation has completed, even after or concurrently with the yeast's 'conditioning phase'. Dry hopping 3-5 days prior to packaging is still the recommended process, except maybe for NEIPAs and other hop drenched beers. We rarely hear about acetaldehyde bombs.

I have the feeling there's something in your process that's more or less unique causing the problem.

 

[kh54s10]

I don't think it has anything to do with S-04, unless the OP just doesn't like the flavor imparted by the yeast. I use S-04 quite a bit and have never gotten acetaldehyde. In fact some of my best beers had S-04 as the yeast.

 

[couchsending]

Never brewed extract so I have no idea if what you’re experiencing might be slightly caused by that, but I doubt it.

You don’t need to oxygenate or aerate S04. You don’t need to rehydrate it either.

For 1.048 wort 1 pack is more than enough, two would be way too much and lead to other issues as well.

The temps you list those are controlled or ambient? How are you measuring the temps.

This is not caused by dry hopping after fermentation. I rarely dry hop during fermentation any more and never experience this issue. You can run into other off flavors by keeping hops in contact with lots of yeast at elevated fermentation temps.

The on my time I experience the dreaded green apple flavor was when using S04 and when fermentation has spiked. It can produce a lot of heat on its own and unless you have good temp control it can get elevated rather quickly. In my instance it did clean up eventually.

Very hoppy beers, regardless of what part of the US they originate from, are incredibly hard to make well as a home brewer especially if you’re bottling. Hop aroma and flavor is the first thing to go when the beer comes in contact with too much oxygen.

Try to make the same recipe with Us05. It’s a much more forgiving yeast. I would be willing to bet you won’t experience any acetaldehyde.

On another note Bry-97 is not the dry version of American Ale II or the anchor ale strain. It’s not really similar to any liquid yeast strain. However it does posses the genetics to be able to bio transform hop compounds.

 

[bw7hb]

The temps you list those are controlled or ambient? How are you measuring the temps.

I have a chest freezer with a temperature controller, the probe is against the side of fermenter with a bit of insulation. The insulation on the probe was probably a bit lacking but I had the temp set to 18C so I can't imagine the beer got higher than around 21C if it was a bit warmer inside the fermenter.

 

[couchsending]

I have a chest freezer with a temperature controller, the probe is against the side of fermenter with a bit of insulation. The insulation on the probe was probably a bit lacking but I had the temp set to 18C so I can't imagine the beer got higher than around 21C if it was a bit warmer inside the fermenter.

Yeah the issue with 04 is even over say 66f it can start to produce some really odd tart like flavors. It’s a rather unforgiving yeast honestly. If I was you I’d try the next batch with 05 before I did anything else differently. That is if you want to stick with dry yeast.

 

[bw7hb]

Ok well I just got the supplies and the LHBS was out of S-04 so I'm going with US-05

I think I'm going to pitch the whole packet in the half batch. According to https://www.brewersfriend.com/yeast-pitch-rate-and-starter-calculator this is about right for the "Pro Brewer" setting - I have no idea which setting on here is "best" but I don't think I'm massively over pitching.

 

[couchsending]

Just be careful it’s easy to end up with Diacetyl when overpitching 05. Make sure you let it warm up over 21c for a few days after fermentation is over and gravity is stable.

 

[bw7hb]

Ok I've pitched the yeast and I'll ferment this one at 22C (it seems US-05 has a higher temperature range than S-04, 18-28C). I only pitched about 2/3 of the packet in the end.

I'll update y'all with how it goes...

Also I'm going to try get a kegging setup before this one's finished. I can't be bothered going through the bottling procedure any more...

 

[bw7hb]

Ok so fermentation never seemed to go off like it usually does, about half the amount of airlock activity and krausen as usual. I was getting worried then I realized that should be expected with a half size batch

I dry hopped yesterday and checked the gravity today (72 hours after pitching yeast) and the gravity is at 1.016 with virtually no airlock activity. The gravity sample smelt and tasted exactly like the previous batches - green apple. I suppose this is to be expected only 3 days into fermentation? Has anyone ever tasted their wort this early on with a US-05 beer, if so what did it taste like?

I'll do another gravity sample and taste in about 2-3 days and see if anything's changed. If not then I might stir up the yeast to try get them working again.

EDIT: I guess this kind of rules out oxidation as the issue - I doubt the beer would have had time to completely ferment into ethanol and oxidize back to acetaldehyde.

 

[deadwolfbones]

Can you get a different source of extract? Maybe try some DME instead?

 

[bw7hb]

I've used the same extract before successfully. I think it must be an infection in my plastic fermenter which has survived two cleans with sodium percarbonate (one after the previous batch and one before this batch) followed by a good starsanning.

I couldn't even taste the hops in yesterday's sample which seems strange. Must be an infection. I'll give this batch another week or so then I'll try a new fermenter.

The first two batches I ever did I only used sodium percarbonate for cleaning and sanitizing so I'm wondering if an infection was introduced into the fermenter in the second batch (first was fine).

 

[bw7hb]

The gravity has been stable for 3 days now. It tastes identical to all the previous batches with the really bad off flavor.
I've gone ahead and dumped the beer. Probably a bad idea to dump this early but past experience tells me it's not going to improve.

I think I must have a really bad acetobacter infection.
I understand it needs oxygen - does anyone know roughly how much oxygen it will take for acetobacter to ruin a beer? For example leave the fermenter open for a few days, or just open the lid once during fermentation.
Maybe I'm getting enough oxygen in there during the dry hop for acetobacter to run amok on on my beer which would explain why it's only happened to my dry hopped beers.
I did see a fruit fly near where I brew/ferment a few days ago.

 

[kh54s10]

The question of how much oxygen will lead to off flavors will get you wildly varying opinions. Some say they detect oxidization if they don't do closed transfers. I don't have the setup for that and have dry hopped, siphoned to a bottling bucket for bottling and have never had issues bad enough to even say I had oxidation at all.

It is possible to get microbes in plastic in a way that the only real solution is to replace the plastic.

I would try a new fermenter.

 

[bw7hb]

An update on this.
I've since got a new fermenter and brewed a different recipe which turned out great. It didn't have any dry hops.

After that I decided to try the NEIPA again in the new fermenter and it smells and tastes exactly like the previous ones. I didn't smell the off flavor prior to dry hopping so I'm certain it has something to do with dry hopping.

After extensive research I think it might be diacetyl caused by dry hop creep, and the buttery aroma usually associated with diacetyl might be mixed in with the hop aroma creating a very weird off flavor/aroma that I didn't initially detect as diacetyl.

I was drinking a real NEIPA from the shop and poured a bit of my latest attempt to compare.
When I smelt my one this time all I could smell was a horrible smell that is somewhat reminiscent of butter - without the fruity smell that I could detect before I'd drunk the proper NEIPA.
I reckon I couldn't smell the hop aroma of my beer since I'd just been drinking a hoppy beer, and therefore only picked up the other aroma which I think is diacetyl. An excellent diagnosis/smelling technique if this proves to be correct

I'd be glad of any suggestions as to how to try get rid of the diacetyl in this latest batch. Should I just remove from the fridge and let it sit for a week or so at room temperature?

EDIT: I'm pretty sure all of my attempts at this NEIPA have been dry hopped only a few days prior to cold crashing so that may help explain why diacetyl hasn't been cleaned up by the yeast.

 

[IslandLizard]

Thanks for the update!

Should I just remove from the fridge and let it sit for a week or so at room temperature?

To do a diacetyl rest at this point, you still need yeast in suspension. Do you think there is still enough in there? Or maybe add a fresh yeast starter at high krausen. Did you use US-05? Again, prevent any air/O2 exposure, whatever you do.

Next time give it a D-rest at 72-74F when adding the last dry hop, or during the last 4 days of the last dry hop. Perhaps taste some before cold crashing to make sure the diacetyl has been converted, and give it a few extra days if necessary.

It's a very strange phenomenon though. Maybe you are super sensitive to diacetyl or whatever it creates with the hops oils.

 

[bw7hb]

It's been cold crashing for 2.5 days now so probably not much yeast left in suspension. I used S-04 this time.
I'm actually using a BrewKeg now and it's under pressure; it would be difficult to pitch more yeast at this point.
I think I'm going to turn the fridge off for a week or so and see if I can get any conversion otherwise I might just dump it and start again.

It looks like someone else has confused diacetyl with acetaldehyde so that gives me a bit of hope that this is actually the issue.

 

[IslandLizard]

You could rouse the yeast back into suspension by inverting the keg a few times or rolling it.
Together with a temp rise to 72-74F that may be enough. I'm saying 72-74F as regular 68-70F conditioning at the end of fermentation doesn't seem to do it. After active fermentation is done, how long do you condition it at 68-70F?

On those Brewkegs, can't you remove and reseal the lid to add stuff?

Green apples and butter are very different off flavors. But I can see how a NEIPA dry hop load can change the butter perception. The malt background is so subdued too.

 

[bw7hb]

I already removed the settled-out yeast from the collection bottle before I dry hopped, as I dry hopped via the collection bottle.
Hopefully there will be enough in suspension.

I think I'll try leaving it for a few days and if nothing changes I could de-pressurise it and add yeast through the lid and just purge with CO2 after.

If I were to add more yeast should I use the same strain, also how much?

 

[bw7hb]

Interesting podcast on dry hop creep: http://masterbrewerspodcast.com/098-dry-hop-creep

 

[IslandLizard]

I already removed the settled-out yeast from the collection bottle before I dry hopped, as I dry hopped via the collection bottle.
Hopefully there will be enough in suspension.

I think I'll try leaving it for a few days and if nothing changes I could de-pressurise it and add yeast through the lid and just purge with CO2 after.

If I were to add more yeast should I use the same strain, also how much?

Ah, I see. Hope you're lucky and there's still enough left to do the job. Keep rousing, yeast on the bottom isn't doing any work.

Yup, purge the headspace after opening the keg. Or stream CO2 in while removing the lid and adding the yeast starter counterstream. Work fast. But the opening is large, so a few purges afterward will remove most of any O2 that entered.

I would make a 1 liter "vitality' starter from the dry yeast and pitch that at high krausen. It's difficult for yeast to establish itself in an alcohol rich environment with no (easy) fermentables. Perhaps add a little extra sugar along with it. The beer should be at 72-74F so she's ready to get her extra D-rest. You can use any yeast, a medium flocculator would be best IMO, so she doesn't crash out too soon. Give it a few days then taste.

 

[bw7hb]

I left it a few days without adding yeast and it didn't seem to clean up, so I pitched the starter.

4 days later it seems to have fixed the diacetyl but the beer still doesn't smell entirely right. Might just be because it's warm - I'm going to chill it for a few days then try it.

 

[mediant]

What was the cold crash temperature? Do a diacetyl test first before cooling the beer again below 15C, it's very simple and only takes half an hour. In general, you are not supposed to smell the diacetyl at any point during fermentation or maturation, as warm D-rest is not for the yeast. It's to encourage decarboxylation of diacetyl precursor acetolactate.

 

[Soulshine2]

I'm trying to brew a NEIPA but I'm having issues with very strong acetaldehyde / green apple off flavor at bottling time and after a month of bottle conditioning. As I'm fairly new to home brewing I'm using all extract.

The first beer I ever brewed was a pale ale and it worked out very well. I simply used the unlabeled yeast that came with the hopped LME, added some unhopped LME, fermented for seven days then bottled. The beer was clean tasting and just "tasted like beer" after two weeks of bottle conditioning.

Since then I've done three attempts at this NEIPA recipe with various changes to each iteration to try fix what I thought was wrong with the previous batch. Despite these changes all of them have the green apple, almost cidery, off flavor mentioned above. It does seem to die off a bit after a month in the bottle but is still quite strong and by then the beer is looking pretty oxidized and the hop aroma is probably gone anyway.

I bottled the third attempt last night - it has the same taste and it seems just as strong as previous batches despite making some decent process improvements to this batch. I realize it hasn't had a chance to bottle condition yet, but based on the previous batches still having the taste after 3-4 weeks, I don't have high hopes for it.

Some of the things I've done to try fix this are listed below:

• Re-hydrated the yeast before pitching.
• Oxygenated the wort the best I could by shaking it around for a few minutes before pitching.
• Kept the wort at 18°C for first 3 days of fermentation and slowly increased it to 21°C over the next few days.
• Left it in the primary for 13 days (as opposed to the 7-9 days I did for the first batch) before cold crashing.
• Dry hopped only once at day 10 of fermentation instead of twice to try and avoid oxygen contact.

All of the brews have had an OG of 1.048 and FG of 1.014. I'm using starsan and I'm pretty confident with my sanitation practices. I use carbonation drops instead of priming sugar.

I'm starting to wonder if S-04 is just a bad yeast. Or maybe I need to leave it in the primary for even longer? But from what I've read S-04 should be a pretty fast yeast to finish and clean up.

Any thoughts on this would be much appreciated.

I always wonder to myself about the whole NEIPA thing everyone goes to,especially beginners. Not saying its wrong, Im just not into them at all.
But besides that what I AM into that ive found since adopting its procedure has turned out some good beer ,better than not doing it anyway, is kraeusening with saved sterile unfermented wort at bottling. Adds no sugars other than what you made the wort/beer with in the beginning. Hopped or not , your choice. No carbonation drops ,etc. In the end its just beer. I make 5 and 6 gallon batches so my addition is basically 1.2 qts . I add half to the bottling bucket before racking,so it gets thoroughly mixed , the rest goes in at the end, gently stirring to mix and mingle again and then bottle.
Other advice is same as given, S-04 is a love /hate yeast. I used it only once and cant say it made what I was looking for exactly.

 

[bw7hb]

I did a forced diacetyl test before chilling and couldn't detect any diacetyl.
I tasted a bit just now after it had been chilling for 24hr and now it tastes like it has acetaldehyde (also smelt like that prior to chilling).
I think I've probably been dealing with both diacetyl and acetaldehyde lol.

Probably going to dump this lot and start again.
Next time I'll sample the beer before dry hopping to ensure there are no off-flavors at that stage.
Also I think I'm going to dry hop at about 5C to prevent any yeast activity after dry hopping. It'll be staying in chilled kegs for the rest of it's life so why not

 

[bw7hb]

For the latest attempt I dry hopped with only 75g (half mosaic, half citra) at day 2 of fermentation and left it to finish off for another week. US-05 yeast. Fermentation seemed to go very well.
Same result, so obviously dry hop creep wasn't the issue.

It seems like the beer has about 3-4 off flavors. Acetaldehyde is the main one, then diacetyl, then astringency, then a slight metallic aroma.

I hate to say this but I'm going to give up on the NEIPA for now and do a few beers that aren't dry hopped, to try prove that it's not a sanitation issue or something.

 

[bw7hb]

Update six months later:

Since my last post I've attempted numerous beers, all of which have had very severe off flavours/aromas - mostly acetaldehyde but also with some other issues such as diacetyl and solvent-like off flavours. The beers were very simple with no dry hopping or anything fancy, mostly using US-05 yeast. I re-hydrated the yeast, aerated the wort, even tried yeast nutrient, to no avail. The fermentations didn't seem to be going very well as they all took at least 24 hours before I could see any signs of fermentation and took about 10-12 days to finish, leaving me with some disgusting apple juice beer.

I was one more attempt away from giving up on home brewing for ever, when I finally made a drinkable beer. The difference with this one was that I pitched twice as much yeast. Also I used a different yeast, the yeast that comes with Black Rock extract kits which I believe is S-33. There were signs of fermentation just 2 hours after pitching and it finished in 7 days, and NO GREEN APPLE BOMB!!!

My next beer will be using US-05 or S-04 and I'm going to pitch two packets and hopefully that clears this nonsense up for good.

 

[Dgallo]

Update six months later:

Since my last post I've attempted numerous beers, all of which have had very severe off flavours/aromas - mostly acetaldehyde but also with some other issues such as diacetyl and solvent-like off flavours. The beers were very simple with no dry hopping or anything fancy, mostly using US-05 yeast. I re-hydrated the yeast, aerated the wort, even tried yeast nutrient, to no avail. The fermentations didn't seem to be going very well as they all took at least 24 hours before I could see any signs of fermentation and took about 10-12 days to finish, leaving me with some disgusting apple juice beer.

I was one more attempt away from giving up on home brewing for ever, when I finally made a drinkable beer. The difference with this one was that I pitched twice as much yeast. Also I used a different yeast, the yeast that comes with Black Rock extract kits which I believe is S-33. There were signs of fermentation just 2 hours after pitching and it finished in 7 days, and NO GREEN APPLE BOMB!!!

My next beer will be using US-05 or S-04 and I'm going to pitch two packets and hopefully that clears this nonsense up for good.

Did you mention if you have temp control?

 

[kh54s10]

There is something else going on here unless all your beers have been very high gravity recipes. One pack should be good to about 1.070 without producing off flavors. I have done one pack in higher gravity beers than that with no off flavors (at least that I can detect).

 

[passedpawn]

Update six months later:

Since my last post I've attempted numerous beers, all of which have had very severe off flavours/aromas - mostly acetaldehyde but also with some other issues such as diacetyl and solvent-like off flavours. The beers were very simple with no dry hopping or anything fancy, mostly using US-05 yeast. I re-hydrated the yeast, aerated the wort, even tried yeast nutrient, to no avail. The fermentations didn't seem to be going very well as they all took at least 24 hours before I could see any signs of fermentation and took about 10-12 days to finish, leaving me with some disgusting apple juice beer.

I was one more attempt away from giving up on home brewing for ever, when I finally made a drinkable beer. The difference with this one was that I pitched twice as much yeast. Also I used a different yeast, the yeast that comes with Black Rock extract kits which I believe is S-33. There were signs of fermentation just 2 hours after pitching and it finished in 7 days, and NO GREEN APPLE BOMB!!!

My next beer will be using US-05 or S-04 and I'm going to pitch two packets and hopefully that clears this nonsense up for good.

Back when I started brewing, I had a couple of bouts of acetaldehyde. Man, when that awful green apple taste is there, it's totally undrinkable. Those went down the drain.

In my case, it was caused by a dirty beet that I sliced and added to one fermentor. I then used that yeast to make another beer. So my money's on infection.

Acetaldehyde is part of the normal yeast fermentation cycle, but it gets converted to alcohol immediately, assuming healthy yeast. So, if your yeast wasn't healthy, I suppose you could run into problems. In your case, it's highly unlikely that you've had so many bad batches of yeast. Dry yeast is very dependable. I've made a zillion beers with dry yeast, usually one packet per carboy, no problem. I don't oxygenate my wort, but I do usually rehydrate the yeast.

 

[bw7hb]

Did you mention if you have temp control?

Yes, I have decent temp control for all fermentations.

There is something else going on here unless all your beers have been very high gravity recipes. One pack should be good to about 1.070 without producing off flavors. I have done one pack in higher gravity beers than that with no off flavors (at least that I can detect).

All the beers have been around 1.050. I used to think I was getting an infection in the beer, however the seemingly sluggish fermentation is what led me to try pitching more yeast. I guess I should try US-05 or S-04 again with the increased pitch rate and see how that goes.

One other thing I did differently with this batch was sanitized the fermenter with boiling water (stainless fermenter) rather than starsan (still used starsan for other equipment). I wonder if there was some infection that was surviving starsan? But that still wouldn't explain the sluggish fermentation.

I'll report back after my next brew.

 

[kh54s10]

As I said previously, I believe something else is going on. US-05 has been described as sluggish. But mostly in how long it takes to get to FG. Even at 24+ hours lag time you should not be getting any off flavors. Pitching more yeast won't hurt, but at the gravity you quote you should not need more than one pack. I have made much higher gravity beers and used only one pack without any issues.

 

[Bobby_M]

Decent temp control can be interpreted a lot of ways. Do you have an active control system wuth a thermostat that will heat or cool the fermenter?

Post ferment temp crash happens normally and it stunts the yeast at the worst time; when they would otherwise clean up acytaldehyde and diacetyl. Actively warming even a couple degrees at that time makes a real difference. Double pitching yeast effected the same end, but there are beer flavor reasons why it wont always be the best way.

 

[bw7hb]

So I just took a sample of my latest attempt, in which I pitched two packets of US-05 into a 21 liter batch. Same **** different day. Hydrometer reading has reached target SG but it's a green apple bomb. I wouldn't even know it was supposed to be beer if I didn't know what it was, that's how bad it is. All I get on the nose is this intense apple-y aroma.

Signs of fermentation activity seemed to finish up a bit quicker than my previous attempts with US-05, probably because of the higher pitch rate, also I fermented this one a bit warmer. It's only been six days since pitch so I will probably leave it another week or so and see if it changes, but past batches haven't improved at all after two weeks so I'm not very hopeful.

Decent temp control can be interpreted a lot of ways. Do you have an active control system wuth a thermostat that will heat or cool the fermenter?

Yes I have a chest freezer / heat belt setup. Temperature probe is taped to side of fermenter with insulation on the outside. There's no way it's a temperature issue.

At this point I guess it has to be an infection, and maybe I just got lucky on my previous batch with S-33. I noticed S-33 kicks off fermentation a lot quicker than US-05 so maybe that helped ward off an infection?

 

[Dgallo]

So I just took a sample of my latest attempt, in which I pitched two packets of US-05 into a 21 liter batch. Same **** different day. Hydrometer reading has reached target SG but it's a green apple bomb. I wouldn't even know it was supposed to be beer if I didn't know what it was, that's how bad it is. All I get on the nose is this intense apple-y aroma.

Signs of fermentation activity seemed to finish up a bit quicker than my previous attempts with US-05, probably because of the higher pitch rate, also I fermented this one a bit warmer. It's only been six days since pitch so I will probably leave it another week or so and see if it changes, but past batches haven't improved at all after two weeks so I'm not very hopeful.


Yes I have a chest freezer / heat belt setup. Temperature probe is taped to side of fermenter with insulation on the outside. There's no way it's a temperature issue.

At this point I guess it has to be an infection, and maybe I just got lucky on my previous batch with S-33. I noticed S-33 kicks off fermentation a lot quicker than US-05 so maybe that helped ward off an infection?

If I’m you and the funds are available, I’m getting all new post boil equipment and fermenters just to be safe but acetaldehyde is almost always a fermentation or oxidation issue
https://www.google.com/amp/s/beerandbrewing.com/amp/off-flavor-of-the-week-acetaldehyde/

 

[bw7hb]

It's been sitting in the primary for 16 days now and I just took another sample. I noticed while taking the sample that the surface of the beer was very clean, no pellicles that would indicate infection, just a few small patches of bubbles. The gravity hasn't changed since 10 days ago, the green apple aroma is not quite as intense as it was, but now there's a strong white wine aroma.

I'm wondering if it's oxidized now. Sherry is a common description for oxidized beer, is it similar to white wine? (I've never tasted sherry). From what I can see it's like a sweeter version of white wine which would match the aroma of my beer pretty well.

As @Dgallo mentioned oxidation could also be the cause of the acetaldehyde, but I'm just at a loss as to how it could be so bad?

Interestingly, the previous batch (which didn't have this issue) was done in a pressure fermenter which would be a lot safer from oxidation issues. Perhaps my plastic fermenter has a small leak somewhere, or the lid isn't sealing properly. There can't be a massive hole as the airlock was bubbling during fermentation, but would oxygen ingress through a tiny hole / poor seal be enough to do this to a beer?

 

[kh54s10]

As @Dgallo mentioned oxidation could also be the cause of the acetaldehyde, but I'm just at a loss as to how it could be so bad?

Interestingly, the previous batch (which didn't have this issue) was done in a pressure fermenter which would be a lot safer from oxidation issues. Perhaps my plastic fermenter has a small leak somewhere, or the lid isn't sealing properly. There can't be a massive hole as the airlock was bubbling during fermentation, but would oxygen ingress through a tiny hole / poor seal be enough to do this to a beer?

I doubt a small pinhole could cause such a bad problem. There are tons of threads where people ask why their beer never fermented. Then when diagnosed, it turns out their worry was because they never say any activity in the airlock and the beer had in fact fully fermented. Just a leaky lid on a bucket. And those beers did not turn out an oxidized mess.

 

[Dgallo]

If you’re a somewhat experienced brewer( don’t take that any type of way, I don’t know you personal so I’m just stateibg generally) and under stand the need for a healthy fermentation and implemented that in your practices, and you don’t have the issue with any other beer style than NEIPAS or hoppy beer styles, I would almost guarantee to you that it’s an oxidation issue. Hoppy styles are notoriously susceptible to oxidation due to how easy the excess polyphenols from the hops oxidize. It can turn to apple cider/sherry wine sweetness and stale the hops completely. I ran into this issue for half a year until Justin from Sloop Brewing was kind enough to try a few of my beers and help me improve on my process. They all started out ok, then would get cider lik and drop in overall hop flavor/aroma.
A lot of ppl use 04 without an issue so it’s extremely hard for me to believe after multiple attempts with the same yeast (multiple different growth generations from the supplier) that it keeps happening. I would think it’s a process issue.

 

[Pennine]

what size fermenter are you using?