IPA 's Darkening with Age

[BykerBrewer]

Any idea as to possible mechanisms by which a beer could could go from looking like the beer on the left (bottle conditioned for 2 weeks) to the beer on the right (bottle conditioned for 6 weeks)... Yes, these are 2 beers from the exact same batch... & all my IPA's have ended up this way...

I have tried everything I can think of to reduce oxygen exposure & have cleaned and sanitized every single thing that comes into contact with the yeast/boiled wort/beer. But despite my greatest efforts, all my IPA's have suffered from the exact same issue.

Thank you for any ideas!

 

[day_trippr]

Oxidation. It's getting in there somehow...

Cheers!

 

[brick_haus]

The times that this has happened to me I have blamed oxygenation. Since almost completely eliminating o2 exposure I Have not had this occur. A tiny bit of O2 can destroy a great hoppy beer quickly. I have also noticed a pronounced change in flavor (sweeter) and a total lack of hop aroma when this occurred.

 

[BykerBrewer]

The times that this has happened to me I have blamed oxygenation. Since almost completely eliminating o2 exposure I Have not had this occur. A tiny bit of O2 can destroy a great hoppy beer quickly. I have also noticed a pronounced change in flavor (sweeter) and a total lack of hop aroma when this occurred.

Do you mean you started kegging? Or how did you eliminate o2 exposure? It just seems that if my beers are oxidizing, it would seem that everyones would oxidize.

I place the carboy into my temperature regulated fermentation fridge right after pitching my yeast, never remove the bung except to add my dry hops and even then the bung is removed for only a few seconds. And on bottling day, from the time I start siphoning into my bottling bucket to the time all bottles are capped is 5 minutes max (one gallon batches). I am not eliminating the possibility that this could be oxidation, it just seems that everyone would have severe oxidation issues if it is occurring to me with the little exposure to oxygen that my beers receive.

That said, I agree, signs definitely point to oxidation. I just wanted to see if anyone had another possible solution, because oxidation is a difficult solution for me to accept for the previously stated reasons. Cheers!

 

[brick_haus]

To help minimize O2, i began purging my kegs and bottles with CO2 prior to filling. I don't use a bucket. You could be getting O2 exposure during the transfer to the bottling bucket and in the bottle. It doesn't take much.

 

[jddevinn]

OOOOO-xidation

It is a problem a lot of people have!

Those few minutes are enough time for a lot of 02 exchange to happen. Bottling normally gives a little bit of leeway as the yeast will consume the O2, however the precipitate reactions that will cause the color change, hop fade, and staleing a happening at the same time.

Is it possible your syphon has a small crack that allows air in? Gasket isn't sealing perfect?
Are you cold crashing?
Tried O2 scavenging caps?
How are you transferring from fermenter to bottling bucket?
How are you adding the priming sugar?

 

[BykerBrewer]

OOOOO-xidation

It is a problem a lot of people have!

Those few minutes are enough time for a lot of 02 exchange to happen. Bottling normally gives a little bit of leeway as the yeast will consume the O2, however the precipitate reactions that will cause the color change, hop fade, and staleing a happening at the same time.

Is it possible your syphon has a small crack that allows air in? Gasket isn't sealing perfect?
Are you cold crashing?
Tried O2 scavenging caps?
How are you transferring from fermenter to bottling bucket?
How are you adding the priming sugar?

Thanks for the response! The only thing I can think of to reduce my beer's oxygen exposure is to keg by beer. There is no apparent crack in my syphon. I do cold crash all my beers. I do not use O2 scavenging caps because I have heard bad things about them. I transfer into bottles by first boiling my priming sugar and placing that solution into my bottling bucket. I then submerge the end of my transfer tubing in the solution within the bottling bucket. Then start the siphon. Once the carboy has been emptied of all but trub, I use my bottling wand to fill my (8) bottles & cap. So it does not take long when you have only 8 bottles to fill & cap. So I just have a hard time imagining I would have such severe oxygenation issues after only a few weeks when many home brewers bottle and cap 50+ bottles on a regular basis. Thanks!

 

[brick_haus]

Hmm, if its not oxidation, i have no idea what it could be. Please let us know when you get it figured out.

 

[olotti]

Thanks for the response! The only thing I can think of to reduce my beer's oxygen exposure is to keg by beer. There is no apparent crack in my syphon. I do cold crash all my beers. I do not use O2 scavenging caps because I have heard bad things about them. I transfer into bottles by first boiling my priming sugar and placing that solution into my bottling bucket. I then submerge the end of my transfer tubing in the solution within the bottling bucket. Then start the siphon. Once the carboy has been emptied of all but trub, I use my bottling wand to fill my (8) bottles & cap. So it does not take long when you have only 8 bottles to fill & cap. So I just have a hard time imagining I would have such severe oxygenation issues after only a few weeks when many home brewers bottle and cap 50+ bottles on a regular basis. Thanks!

I've had the same issues lately. I've had 3 ipas/dipas all with a pound of hops in them oxidize in 2 weeks, crazy, and I'm super careful not to shake the carboy, cause o2 bubbles during racking to the bucket, etc. etc. I just think that the hoppier the beer it can actually increase the rate at which a beer gets oxidized. I realize as long as I bottle I'll always be at risk since there's just no real way to eliminate the O2 unless I buy a CO2 bottle and purge every bottle before racking beer into them. So don't feel alone its a common problem and often why people like us who bottle get into kegging because its extremely frustrating going through the time and money and effort to have this amazing smelling and tasting beer at bottling and then it goes into the toilet never seeing its potential. I did try a different technique in this last heavy ipa and that was fill a bottle, place a cap, fill a bottle, place a cap and do that for 6 beers then crimp the caps, so far so good, I used to just fill the bottles and set aside then when I'd fill 24 Id cap them all so maybe this will work for you too.

 

[BykerBrewer]

I've had the same issues lately. I've had 3 ipas/dipas all with a pound of hops in them oxidize in 2 weeks, crazy, and I'm super careful not to shake the carboy, cause o2 bubbles during racking to the bucket, etc. etc. I just think that the hoppier the beer it can actually increase the rate at which a beer gets oxidized. I realize as long as I bottle I'll always be at risk since there's just no real way to eliminate the O2 unless I buy a CO2 bottle and purge every bottle before racking beer into them. So don't feel alone its a common problem and often why people like us who bottle get into kegging because its extremely frustrating going through the time and money and effort to have this amazing smelling and tasting beer at bottling and then it goes into the toilet never seeing its potential. I did try a different technique in this last heavy ipa and that was fill a bottle, place a cap, fill a bottle, place a cap and do that for 6 beers then crimp the caps, so far so good, I used to just fill the bottles and set aside then when I'd fill 24 Id cap them all so maybe this will work for you too.

Thanks olotti! It definitely can be frustrating. I will give that a try next bottling day. I have three IPA's in the fermenter right now, and I will try a few things (including your cap placing technique) to see if I can find a solution. Will report back! Thanks everyone!

 

[olotti]

Thanks olotti! It definitely can be frustrating. I will give that a try next bottling day. I have three IPA's in the fermenter right now, and I will try a few things (including your cap placing technique) to see if I can find a solution. Will report back! Thanks everyone!

I also used to do a prolonged cold crash of my carboys for like 3-4 days but I think that may have been an issue too as I was getting def suck back with the three piece airlock even with refilling it multiple times with starsan so now I just keep it to 24 hr cold crash and then I just figure the rest will settle when the bottles hit the fridge. The crazy thin and here's where I see the happier the beer can increase oxidation is I've brewed a pale ale and a blonde ale that are both over a month old and crystal clear and no signs of oxidation so I'm convinced the extra hop matter in suspension somehow adds to advancing the effects of oxidation if O2 gets in the syste somewhere.

 

[jddevinn]

Thanks for the response! The only thing I can think of to reduce my beer's oxygen exposure is to keg by beer. There is no apparent crack in my syphon. I do cold crash all my beers. I do not use O2 scavenging caps because I have heard bad things about them. I transfer into bottles by first boiling my priming sugar and placing that solution into my bottling bucket. I then submerge the end of my transfer tubing in the solution within the bottling bucket. Then start the siphon. Once the carboy has been emptied of all but trub, I use my bottling wand to fill my (8) bottles & cap. So it does not take long when you have only 8 bottles to fill & cap. So I just have a hard time imagining I would have such severe oxygenation issues after only a few weeks when many home brewers bottle and cap 50+ bottles on a regular basis. Thanks!

I also used to do a prolonged cold crash of my carboys for like 3-4 days but I think that may have been an issue too as I was getting def suck back with the three piece airlock even with refilling it multiple times with starsan so now I just keep it to 24 hr cold crash and then I just figure the rest will settle when the bottles hit the fridge. The crazy thin and here's where I see the happier the beer can increase oxidation is I've brewed a pale ale and a blonde ale that are both over a month old and crystal clear and no signs of oxidation so I'm convinced the extra hop matter in suspension somehow adds to advancing the effects of oxidation if O2 gets in the syste somewhere.

If you are not cold crashing under positive CO2 pressure you are oxidizing during this process. Even for 24 hours.

Let's assume that air is an ideal gas (close enough) and your carboy is COMPLETELY sealed by the airlock. For round numbers let's assume that you have 1 gallon of airspace. If you drop the temperature from 70°F to 35°F keeping a constant volume (since the carboy is completely sealed) there would be a 1 psi pressure on the outside of the carboy from the temperature (and volume) decrease of the air. Obviously this 1 psi is enough to overcome the airlock. 1 psi is ~28 inches of water column, so this pressure change would also suck StarSan through a 2 foot blow off tube.

OK so we know that the carboy won't hold the vacuum created. What will happen is the volume of gas will contract and suck in air to fill the volume. There is no such thing as a "CO2 blanket" , the air and the CO2 will very quickly diffuse together creating a mixture. The O2 in that air will then oxidize the beer.

 

[olotti]

If you are not cold crashing under positive CO2 pressure you are oxidizing during this process. Even for 24 hours.

Let's assume that air is an ideal gas (close enough) and your carboy is COMPLETELY sealed by the airlock. For round numbers let's assume that you have 1 gallon of airspace. If you drop the temperature from 70°F to 35°F keeping a constant volume (since the carboy is completely sealed) there would be a 1 psi pressure on the outside of the carboy from the temperature (and volume) decrease of the air. Obviously this 1 psi is enough to overcome the airlock. 1 psi is ~28 inches of water column, so this pressure change would also suck StarSan through a 2 foot blow off tube.
View attachment 363110
OK so we know that the carboy won't hold the vacuum created. What will happen is the volume of gas will contract and suck in air to fill the volume. There is no such thing as a "CO2 blanket" , the air and the CO2 will very quickly diffuse together creating a mixture. The O2 in that air will then oxidize the beer.

Wow this is amazing, thank you for posting this. So let me ask this. If I were to obtain a co2 bottle and shoot the co2 into the carboy then put the airlock or just a solid bung back on would this purge the carboy of O2 enough to cold crash.

 

[olotti]

If you are not cold crashing under positive CO2 pressure you are oxidizing during this process. Even for 24 hours.

Let's assume that air is an ideal gas (close enough) and your carboy is COMPLETELY sealed by the airlock. For round numbers let's assume that you have 1 gallon of airspace. If you drop the temperature from 70°F to 35°F keeping a constant volume (since the carboy is completely sealed) there would be a 1 psi pressure on the outside of the carboy from the temperature (and volume) decrease of the air. Obviously this 1 psi is enough to overcome the airlock. 1 psi is ~28 inches of water column, so this pressure change would also suck StarSan through a 2 foot blow off tube.
View attachment 363110
OK so we know that the carboy won't hold the vacuum created. What will happen is the volume of gas will contract and suck in air to fill the volume. There is no such thing as a "CO2 blanket" , the air and the CO2 will very quickly diffuse together creating a mixture. The O2 in that air will then oxidize the beer.

So then there must be a correlation between the increase in hop oils, poly phenols and yeast compounds in suspension that increases the speed at which these beers are oxidized. I say that as I have a blonde ale I bottled a month ago, low ibu and only like 6 oz of hops in the whole beer and it's crystal clear and showing no signs of oxidation while the hoppy IPA and dipas I make with 16oz of hops start to show signs of oxidation in 3 weeks, some recently have started to turn as soon as 2 weeks.

 

[henchman24]

This looks exactly like oxidation to me.

The first step I'd take is to stop cold crashing. I used to cold crash all of my beers in the fermentor, but I started having some similar issues on hoppy beers (I almost always keg... especially hoppy beers). I stopped cold crashing and my issues have completely gone away. I'm to the point where I don't even think of cold crashing in the fermentor and only will do it in the keg. I've gotten much better results that way, and the only downside is a couple of cloudy pours at the beginning.

When I have bottled I only use O2 scavenging caps. I don't know if any really downside or bad things other than they cost a touch more, but caps are so cheap that I don't worry about the extra dollar or two.

 

[jddevinn]

Wow this is amazing, thank you for posting this. So let me ask this. If I were to obtain a co2 bottle and shoot the co2 into the carboy then put the airlock or just a solid bung back on would this purge the carboy of O2 enough to cold crash.

After fermentation is done, if the airlock is tight and doesn't allow any air leakage, than the headspace is already all CO2. The issue becomes when this CO2 is cooled it becomes smaller and the space has to be filled with something else.

I would be afraid to put a solid bung into a carboy. This thread https://www.homebrewtalk.com/showthread.php?p=7419568#post7419568 has a bunch of discussion on this topic. Daytrippers solution is my favorite for carboys https://www.homebrewtalk.com/showpost.php?p=7419568

So then there must be a correlation between the increase in hop oils, poly phenols and yeast compounds in suspension that increases the speed at which these beers are oxidized. I say that as I have a blonde ale I bottled a month ago, low ibu and only like 6 oz of hops in the whole beer and it's crystal clear and showing no signs of oxidation while the hoppy IPA and dipas I make with 16oz of hops start to show signs of oxidation in 3 weeks, some recently have started to turn as soon as 2 weeks.

Beers will oxidize in different ways. Hoppy beers will have the hops fade quickly, really light ones will go dark faster...

Go pop into the thread going on on hot side oxidation and low oxygen brewing for some interesting reading. If you can't get what you want by limiting the O2 exposure it's possible to dose with SMB so that it reacts with the O2 before the beer, although there are some water chemistry impacts.

 

[olotti]

After fermentation is done, if the airlock is tight and doesn't allow any air leakage, than the headspace is already all CO2. The issue becomes when this CO2 is cooled it becomes smaller and the space has to be filled with something else.

I would be afraid to put a solid bung into a carboy. This thread https://www.homebrewtalk.com/showthread.php?p=7419568#post7419568 has a bunch of discussion on this topic. Daytrippers solution is my favorite for carboys https://www.homebrewtalk.com/showpost.php?p=7419568



Beers will oxidize in different ways. Hoppy beers will have the hops fade quickly, really light ones will go dark faster...

Go pop into the thread going on on hot side oxidation and low oxygen brewing for some interesting reading. If you can't get what you want by limiting the O2 exposure it's possible to dose with SMB so that it reacts with the O2 before the beer, although there are some water chemistry impacts.

So what day tripper is doing is cold crashing under positive co2 pressure, am I looking at that right.

 

[jddevinn]

Yep, so when the temperature decreases and the volume of gas in the headspace shrinks instead of pulling in outside air CO2 is pulled in at a very low pressure. I like his way of connecting to a carboy.

 

[olotti]

Yep, so when the temperature decreases and the volume of gas in the headspace shrinks instead of pulling in outside air CO2 is pulled in at a very low pressure. I like his way of connecting to a carboy.

That is slick.

 

[p_p]

Are you storing your bottles cold? That change of color in only 4 weeks is quite extreme.

 

[BykerBrewer]

Just an update to anyone who comes across this thread...

I stopped cold crashing & the issue disappeared. My IPA's are tasting infinitely better. Thank you to everyone who offered their ideas! It feels great to have that one resolved!

 

[tgmartin000]

Excellent. I have an ipa on tap that I think is oxidized. I cold crashed for 3-4 days. Might have to start with gelatin instead.

 

[olotti]

Just an update to anyone who comes across this thread...

I stopped cold crashing & the issue disappeared. My IPA's are tasting infinitely better. Thank you to everyone who offered their ideas! It feels great to have that one resolved!

This is interesting news as I've dealt with the same prob you have so I'm not gonna cold crash this next batch and see what happens. There's lots of hops in it so I'll have to step up my racking game.

 

[jddevinn]

This is interesting news as I've dealt with the same prob you have so I'm not gonna cold crash this next batch and see what happens. There's lots of hops in it so I'll have to step up my racking game.

If you already have kegging equipment you can build a positive pressure connection for the fermenter relativly cheap (see earlier in the thread).

 

[derekcw83]

My IPA's wee doing the same thing. How are yours tasting once the darkness comes around???

I've done 3 things to eliminate oxygen, a couple have been mentioned. No more cold crash. Cap and let sit. But I let mine sit for like a half hour before full capping. And REDUCE HEADSPACE in your bottles. If any leftover oxygen is in the bottle, make sure it's minimal by leaving only 1/2" of headspace in them. Occasionally I'll even visibly see my caps moving from CO2 escaping as it sits on there for a half hour. You're effectively flushing it of oxygen this way. Not sure which has made the biggest difference. But it's working, so I prefer to do every measure possible as long as it has been working for me. My last 3 ipa's have been perfect,and they stay perfect for 2 months. They don't last much longer for other reasons

 

[BykerBrewer]

My IPA's wee doing the same thing. How are yours tasting once the darkness comes around???

I've done 3 things to eliminate oxygen, a couple have been mentioned. No more cold crash. Cap and let sit. But I let mine sit for like a half hour before full capping. And REDUCE HEADSPACE in your bottles. If any leftover oxygen is in the bottle, make sure it's minimal by leaving only 1/2" of headspace in them. Occasionally I'll even visibly see my caps moving from CO2 escaping as it sits on there for a half hour. You're effectively flushing it of oxygen this way. Not sure which has made the biggest difference. But it's working, so I prefer to do every measure possible as long as it has been working for me. My last 3 ipa's have been perfect,and they stay perfect for 2 months. They don't last much longer for other reasons

I hear the descriptors sherry/cardboard thrown around a lot to describe the flavor of oxidized beer. I can't say my beer has ever tasted of cardboard, and I have never had sherry... But the beer does take on a very off-putting sweet/fruity flavor once the color change occurs.

I have never used the bottling/capping method you described but, hey, if its working for you, keep with it! Thanks for sharing!

 

[BykerBrewer]

This is interesting news as I've dealt with the same prob you have so I'm not gonna cold crash this next batch and see what happens. There's lots of hops in it so I'll have to step up my racking game.

Haha well best of luck! I hope doing away with the cold crash serves you as well as it has me!

 

[Yooper]

I hear the descriptors sherry/cardboard thrown around a lot to describe the flavor of oxidized beer. I can't say my beer has ever tasted of cardboard, and I have never had sherry... But the beer does take on a very off-putting sweet/fruity flavor once the color change occurs.

I have never used the bottling/capping method you described but, hey, if its working for you, keep with it! Thanks for sharing!

Remember that only the longest most extreme examples of oxidation would be "cardboard".

The first sign is simpler- a staling or dulling of flavors. Later comes some "sherry" or "brandy" like sweet-ish notes. After that comes darkening, and once it's terrible severe, it may taste like wet paper or cardboard.

 

[day_trippr]

I think it's been fairly well shown that "darkening" starts well before the sweet/sherry notes.
Lots of threads noting darkened pales/ipas that lost their hops with no concurrent mention of sherry...

Cheers!

 

[lupulinaddict]

I haven't been getting color change, but I feel like my last few iPas/dipas have turned sweet when siting in the kegs after a week or too. I have been trying to narrow down why, so I'm glad I found this thread. I am going to make a few more iPas and skip the crash. I like the positive pressure solution. I was wondering about a few things if I can change to help keep out the oxygen.

If I don't secondary to prevent oxygen, but still need to dry hop, should I put it in and try to lightly swirl the carboy? I know if you do that the airlock bubbles, would that push out the oxygen?

Also, when racking to the keg, is a co2 purge after filling enough to push out any oxygen from the transfer?

 

[Yooper]

I think it's been fairly well shown that "darkening" starts well before the sweet/sherry notes.
Lots of threads noting darkened pales/ipas that lost their hops with no concurrent mention of sherry...

Cheers!

Sometimes. Sometimes not. It's a process, not that everything happens individually. Sometimes the first sign of oxidation is that "sweet" flavor, which may be a "loss of hops" to some. That can happen before darkening, concurrently, or after.

 

[Yooper]

I haven't been getting color change, but I feel like my last few iPas/dipas have turned sweet when siting in the kegs after a week or too. I have been trying to narrow down why, so I'm glad I found this thread. I am going to make a few more iPas and skip the crash. I like the positive pressure solution. I was wondering about a few things if I can change to help keep out the oxygen.

If I don't secondary to prevent oxygen, but still need to dry hop, should I put it in and try to lightly swirl the carboy? I know if you do that the airlock bubbles, would that push out the oxygen?

Also, when racking to the keg, is a co2 purge after filling enough to push out any oxygen from the transfer?

No to swirling! Whenever a carboy is opened, particularly after fermentation slows, there is just as much oxygen as anything else. I guess in theory that some of the dissolved c02 could be released during swirling, but it's much more likely that swirling would provide greater surface area for room air and oxygen to impact the beer. If the airlock bubbles, that just means that the pressure inside is greater than the pressure outside, and not that it's only c02 being released.

It's posted elsewhere in the forum in graph form, but it takes like 30 purges at 30 psi to really get rid most of the oxygen. Most of us don't do that. It's helpful to purge the keg first and do a closed transfer, to avoid oxygen pickup.

 

[inkman15]

I'm interested as to why there's hesitancy to use a solid bung during cold crash. Can someone explain that to me?

I had this darkening happen to me recently with a Galaxy IPA that I bottled. It was delicious at the gravity sample but after 2 weeks in the bottle, it took on that dark hue and the flavors got muted.

Followed the same process (cold crash with solid bung) on a recent IPA that I kegged and the beer is still delicious after a month.

Clearly I oxidized the Galaxy one, but I'm thinking it happened during the bottling process and not during cold crash.

 

[jddevinn]

OK, so if you put a solid bung into the top of the carboy and actually seal you will develop 2psi pressure on the outside of your carboy due to the vacuum created from the gas cooling. If glass you don't want 2psi pressure, if plasic you will collapse the carboy, if you have a conical you are already set up for positive pressure. If you do not create a vacuum then you have an air leak and oxidize the beer, if you pull the bung before the temperature (and pressure) returns to normal you will pull air into the vacuum and oxidize the beer.

 

[inkman15]

OK, so if you put a solid bung into the top of the carboy and actually seal you will develop 2psi pressure on the outside of your carboy due to the vacuum created from the gas cooling. If glass you don't want 2psi pressure, if plasic you will collapse the carboy, if you have a conical you are already set up for positive pressure. If you do not create a vacuum then you have an air leak and oxidize the beer, if you pull the bung before the temperature (and pressure) returns to normal you will pull air into the vacuum and oxidize the beer.

So, I use Better Bottles. I don't care, aesthetically speaking, if the carboy collapses at all since they are so durable. What you're saying is that if I don't allow it to "un-collapse" before pulling the bung, there's a rush of O2 introduced?

 

[jddevinn]

As long as you don't care that your fermenter collapses, you actually get it to fully seal and allow the CO2 that is in the head space to come back to temperature I suppose not.

You may find that this takes a long time though. The solubility of CO2 into beer increases as temperature goes down and increases as pressure goes down. If you allow the pressure to stay the same by collapsing the fermenter some (probably a small amount) of the CO2 in the headspace will go into solution into the beer. When the headspace returns to temperature the CO2 will expand most of the way back to it's original volume but some of the CO2 will remain dissolved in the beer. You will either have to wait for the CO2 to offgas from the warmer beer or allow some of the air to come in and take its place.

Certainly better than allowing air to come in during cold crash, and better than a vacuum on a carboy.... but I'd still just get the minimum amount of hardware necessary to cold crash under pressure.

 

[thiagomdm]

Just an update to anyone who comes across this thread...

I stopped cold crashing & the issue disappeared. My IPA's are tasting infinitely better. Thank you to everyone who offered their ideas! It feels great to have that one resolved!

that's great news. is it still working out good just by skipping the cold crash?

old topic but i have been researching for cases like this since i have been going through this issue with lots of batches. the beers get darker with very little time (even if stored in the fridge) and completely lose their hop aroma and taste. some bottles turn out good, some don't (most).

I thought just letting it sit for a few days or weeks in the fridge would solve my problem. Turns out it didn't.

i did skip cold crashing one time and the batch came out nice. will do that again and hope it works out.

 

[El Nino]

Just an update to anyone who comes across this thread...

I stopped cold crashing & the issue disappeared. My IPA's are tasting infinitely better. Thank you to everyone who offered their ideas! It feels great to have that one resolved!

Good info! Glad I came across this, as I was recently wondering what would work better between cold crashing and putting a filter / rubber band over my siphon when transferring to a bucket.

I'm guessing the suck back caused by cold crashing causes the oxidation?