# Flavour and Aroma disappear



## Blitzer (22/12/22)

Hi,

I have a keg of Stone and Wood clone on tap for about 3 weeks. Suddenly the aroma has completely disappeared, where before it was quite strong.

The aroma mainly came from a large dry hop of galaxy at day 5 in the fermentation. But what I was wondering is there a reason it would suddenly disappear such as an infection? I did change the keg line as well yesterday as it was pouring a lot of foam previously and thought that may solve the issue.

Any help would be appreciated so I can avoid what I have done in the future!

Thanks!


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## JDW81 (22/12/22)

Lots of things can make the hop flavour and aroma disappear. Have you noticed any other strange or odd flavours?

The two most common ones would be:
1: Oxidation: Not early or sufficient enough to give you that wet cardboard flavour, but is a common cause of loss of flavours/aromas.
2: Time: Hop flavour and aroma will always diminish with the passage of time. With heavily hopped beers it is more pronounced, but with hoppy beers (as a general rule) fresh is best - usually the first 1-2 weeks.

I suspect its a combination of the 2 above issues.

JD


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## KegLand-com-au (23/12/22)

I would totally agree with this. Oxidation absolutely kills fresh hop aroma.

Closed transfers are really a great way to go if you are not doing this already.

Also one issue that we do not often talk about is the issue with silicone keg lid o-rings. Many customers thing that if a keg is under pressure that the oxygen will not get in but this is completely false. Oxygen can pass through silicone fairly fast and fairly easily and even when the keg is under pressure the process of diffusion still allows oxygen to get into get into the beer. The keg lid o-ring is a large o-ring with lots of cross sectional area and as a result of this the transmission rate is high too.

Also in the past decade we have seen a large movement of customers choosing Silicone as the keg lid o-ring choice because its:
1. Chemical resistant
2. Has very good spring properties and doesn't compress flat like the old nitrile o-rings
3. Is soft and can tolerate poor lid alignment
Despite these great features above the main issue is that silicone has terrible oxygen transmission rate and has orders of magnitude higher oxygen transmission rate than other rubbers.

We have been trying to educate customers on this topic but customers keep purchasing silicone o-rings unfortunately and it's probably our fault for not doing more education on this subject.

The oxygen permeability of silicone is well known and well documented but not spoken about in home brewing for some reason. Similar silicone was put into contact lenses years ago and the high oxygen permeability allowed "extended wear contact lenses" to exist. The high oxygen flow through the silicone material allowed people to wear contact lenses for weeks at a time which previously was not possible.

We did spend a lot of time and money doing a lot of testing on o-rings and rubber compounds and we came up with this o-ring type:








Low2 Cornelius Keg Lid O-Ring


Suitable for any 19L, 9.5L Corny Keg Ball Lock or Pin Lock.




www.kegland.com.au





This material has way higher oxygen barrier, it doesn't perish like the old nitrile o-rings, has similar chemical resistance to silicone and is similarly soft. It has ever so slightly worse spring properties but still way better than the older nitrile o-rings. For the sake of $2 I would highly recommend this upgrade.


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## Blitzer (23/12/22)

Thanks both for the replies. They make sense, if oxygen came in as part of transfer would it be possible that it scrubs aroma later (I.e 3 weeks in)? Or more likely due to continual oxygen coming through the keg lid as mentioned.

I must admit I'm not sure what wet cardboard flavour would taste like.. I'll see if I can get someone to diagnose if they notice it


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## rayhaynes62 (24/12/22)

KegLand-com-au said:


> I would totally agree with this. Oxidation absolutely kills fresh hop aroma.
> 
> Closed transfers are really a great way to go if you are not doing this already.
> 
> ...


The one thing you are missing here is the keg is under positive pressure from within do it would be impossible for the oxygen to infiltrate while the CO2 is coming out.


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## rayhaynes62 (24/12/22)

rayhaynes62 said:


> The one thing you are missing here is the keg is under positive pressure from within do it would be impossible for the oxygen to infiltrate while the CO2 is coming out.


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## S.E (26/12/22)

Blitzer said:


> The aroma mainly came from a large dry hop of galaxy at day 5 in the fermentation.


You can always add more dry hops to the keg. Dry hopping was traditionally done in the cask, not so much in the fermenter. Just pop the lid off your keg and add more hops, give it a day or two and you’ll have your hop aroma back again.

Only issue with keg hopping is the dip tube and/or beer line and connections can block up but you can use a hop sock or similar.

Casks are sometimes re opened and dry hopped just before they are sent out from the brewery so the aroma is fresh when they are tapped a few days later.


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## S.E (26/12/22)

rayhaynes62 said:


> The one thing you are missing here is the keg is under positive pressure from within do it would be impossible for the oxygen to infiltrate while the CO2 is coming out.


If you re read the post it was explained “Oxygen can pass through silicone fairly fast and fairly easily and even when the keg is under pressure”.

Gasses don’t behave as you would expect and can pass from a lower to higher pressure apparently.


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## MHB (26/12/22)

Close, call it Partial Pressure and you will be even closer.

It’s the concentration of molecules of each gas and they have to be looked at individually.
In a given volume at any pressure we can calculate how many molecules there are. The bigger the difference between the sides of a semi/permeable membrane, the concentration of the gasses and the temperature will all affect the rate gasses pass through. As will the permeability of the membrane.

But yes the O2 outside the keg will treat the inside like a vacuum (inside an O2 free keg) and will try to get in. The high partial pressure of CO2 in the keg will be doing the opposite and trying to get out.
How fast this is going to happen is a different question. The biggest variable being the material of the seals I suspect.
Mark


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## S.E (26/12/22)

MHB said:


> How fast this is going to happen is a different question. The biggest variable being the material of the seals I suspect.


Not even close I’m afraid, the biggest variable will be the container itself. For instance a wooden cask will be more permeable than a stainless steel one. The seals will be negligible in comparison.

I think the reason the aroma has disappeared is not really in question any longer, everyone seems to be agreeing on that.

What are your thoughts on fixing the problem? I have suggested adding more dry hops to the keg. Would you agree or do you have any other ideas?


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## MHB (26/12/22)

I was talking about beer in a corny keg (or similar), which is what the OP was asking about.

Agreed the container would be the biggest factor, but given that we are talking impermeable Stainless, the next place to look would be the hatch O-Ring. What Keg-Land said is true Silicone wouldn’t be my first choice.

I would question if enough O2 is getting into a pressurise keg to have much effect on either hop flavour or aroma in as short a time as weeks. It would be a much more important consideration if you were going to vintage a beer for months or years.

I suspect there will be a lot of components to the solution rather than a magic bullet.
We know that O2 will harm both flavour and aroma, if you want to make highly hopped beers that are stable for more than a week or two. You would really need to look at Low DO brewing from start to finish of the brewing, fermenting and transfer processes. I suspect that the amount of O2 picked up as far back in the process as mashing in will be far more important than what will creep in through a keg hatch seal.
Think about HSA and start excluding O2 from the start.
There are a bunch of processes that will contribute to staling, a lot of these involve Oxygen that is already in the wort tied up in other chemicals, these can be rearranged liberating Oxygen ions that will then do more harm. One of these is involved in the oxidisation of lipids by Lipoxygenase, that can be minimised by getting your pH right during mashing and boiling.
Short boils won’t be a help and longer (90 minute+) will do more to stabilise the beer. The pH of the finished beer really should be in that 4.0-4.2 range (for most beers) or you can expect problems.

There is a fair bit of evidence that dry hopped beers are inherently unstable so the more you can weight your hops toward kettle additions the more stable the flavours should be.

That doesn’t give you the huge hop aroma, many brewers/drinkers are looking for but good brewing practice will help to stabilise a lot of the beer flavours.
Remember to that when it comes to hops, more isn’t always better, you can reach the point were more hops are largely going to waste as lots of hops can block more from going into solution.

Maybe the best thing to do is to brew smaller batches and drink them quickly, dry hop them as hard as you like but don’t expect them to be really stable for long.
Mark

PS - I really question the benefits of short boils, I think they are doing a lot more harm than people realise.
M


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## S.E (26/12/22)

MHB said:


> I was talking about beer in a corny keg (or similar), which is what the OP was asking about.


You are really going off on a tangent here Mark, no more xmas beers for that man!

OP hasn’t mentioned corny kegs (or if has perhaps it is me that needs to take a beer break?)

Op has mentioned “The aroma mainly came from a large dry hop of galaxy at day 5 in the fermentation”.

So unless the fermenter was completely sealed and transfer completely O2 free you can’t really blame the seal on the keg or cask whatever it is made of?

Home brewing is a simple hobby that can be over complicated by commercial practices if you try to follow them without good reason.

In this case I would just chuck more hops in to the keg and drink it within a week or two. If OP wants to keep it for any extended time then look at keeping the whole brewing process O2 free.


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## peteru (26/12/22)

The OP did mention a keg (first few words of the post) and it is reasonable to assume that in a home brew situation it is most likely to be a ball lock corny.

What is missing, is enough detail to perform any useful troubleshooting. Some of the classic signs of oxidisation are darkening of the beer and other flavour changes, such as sherry/card board notes. If those are also present, then O₂ ingress at some point (most likely packaging) would be high on the list of possible causes.

I've been on a quest to eliminate as much exposure to O₂ (past high krausen) as possible for the last half a decade or so. I believe I have many of the significant contributors under control. For my setup and process it makes sense to pursue incremental improvements, such as better keg lid seals. On the other hand, if the OP is still at a stage where they are transferring from fermenter to keg using a siphon between two vessels open to the atmosphere, then the keg seal won't help as the O₂ contributions from the transfer will be orders of magnitude greater.

One of the things that I can highly recommend is joining a good homebrew club and participating in / hosting collab brew days. There's a lot you can learn by observing other people brew. Similarly, you can get many useful tips and suggestions when others join your brew day and comment on your process.


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## S.E (27/12/22)

peteru said:


> The OP did mention a keg (first few words of the post) and it is reasonable to assume that in a home brew situation it is most likely to be a ball lock corny.


If you re read my post I said OP did not mention a Corny keg. It could be a commercial keg and coupler, or it could be a HDPE homebrew keg.

OP said, “I have a keg of Stone and Wood clone on tap for about 3 weeks. Suddenly the aroma has completely disappeared, where before it was quite strong”.

I would not assume from this statement that the problem is caused by a silicone lid seal on a corny keg.

Even if it is a corny with a silicone seal it’s not the first thing I would be looking at. As I said above, unless the fermenter was completely sealed and transfer completely O2 free you can’t really blame the seal.


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## peteru (27/12/22)

Oh, I see, you are here for the argument.


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