Venting keg during transfer = hop aroma loss. Fact or myth?

[CyberFox]

Has it been proven or disproven that venting a keg during transfer leads to hop aroma loss?

Some say it does and others say that if the aroma's in the headspace, then it was never in the beer in the first place. What say you?

 

[Bobby_M]

Does it smell like hops while you're transferring? If it does, yes, you're losing some aroma. The reason you can smell certain hop compounds is that they are very volatile. It may be true that concentrations being in the head space are not in the beer, but if you vent those out of the keg, more will come out of the beer to replace them. Concentrations in a closed system with seek equilibrium.

 

[Broken Crow]

Thanks for bring that up... If I ever do a brew in which a high degree of hoppiness is mandatory, I'll make sure to not sample it before transfer and wait at least a day after it's been in the serving keg, so as to give time for 'expectations' to diminish.
...if I'm unsatisfied, I'll just adjust the volume of hops on my next try.

 

[day_trippr]

fwiw, "venting" beer during transfer implies introducing oxygen.
Oxygen will attenuate character, with aroma going missing first then flavor...

Cheers!|

 

[CyberFox]

fwiw, "venting" beer during transfer implies introducing oxygen.
Oxygen will attenuate character, with aroma going missing first then flavor...

Cheers!|

I didn't know that venting would introduce oxygen. What I mean by "venting" is pushing CO2 into the sending keg and exhausting out of the receiving keg for a transfer. I figured it was like purging a keg, where only CO2 is being pushed in and a mix of oxygen and CO2 are being pushed out. If venting does somehow introduce oxygen, you could attach tubing to the exhaust and direct it into a jar of sanitizer to mitigate oxygen intake. As far as I know, the potential aroma loss would still occur though since it would be bubbing out through the sanitizer.

 

[day_trippr]

Ok, you're use of the word "venting" is non-traditional in this context. We call that a "CO2 push".
And I for one do exhaust the receiving keg via a gas QD and tubing dunked in a bucket of water.

If the receiving keg and all of the tubing used has been purged via liquid or CO2 there should be no oxygen in the system to push out...

Cheers!

 

[AlexKay]

It’s a theoretical way to lose volatiles, as mentioned by @Bobby_M, but I would be very surprised indeed if it was significant in this case. If you were to bubble CO2 through your beer continuously as a means of force carbonating, then maybe.

 

[CyberFox]

Ok, you're use of the word "venting" is non-traditional in this context. We call that a "CO2 push".
And I for one do exhaust the receiving keg via a gas QD and tubing dunked in a bucket of water.

If the receiving keg and all of the tubing used has been purged via liquid or CO2 there should be no oxygen in the system to push out...

Cheers!

I guess "exhaust" is a more accurate term than "venting" then. I only mentioned a CO2 push to highlight a scenario where this exhausting would occur. The only oxygen in the system that might be pushed out when exhausting is any leftover oxygen introduced from dry hopping (either by the hops themselves or if the keg wasn't thoroughly purged after opening the lid and throwing the hops in).

It’s a theoretical way to lose volatiles, as mentioned by @Bobby_M, but I would be very surprised indeed if it was significant in this case. If you were to bubble CO2 through your beer continuously as a means of force carbonating, then maybe.

I agree that it likely wouldn't be a make or break situation, but I thought it was an interesting subject. I've even heard some say that transferring in a fully closed system would still "blow off" aromatics into the pure CO2. Not sure how you could prove or disprove something like that. You can only be so careful.

 

[BigDave1303]

Have you tried doing a closed transfer & returning the venting/exhaust on the receiving keg back to the top of the fermenter to form a closed loop, & use gravity to transfer the liquid? I've done this for the last few years.

 

[CyberFox]

That's exactly what I'm planning to start doing from now on! Glad to hear it works for you.

I've been fermenting in a carboy and using a carboy cap to inject CO2 into the carboy and transfer through a racking cane into the liquid post of a keg. I don't cold crash due to the vacuum (oxidation) and racking with dry hops is a PITA.

My plan is to start fermenting in a keg with a floating dip tube and do a fully closed transfer like you described. It seems like the most foolproof way to prevent oxidation.

I was planning to have both the sending and receiving kegs at the same pressure, elevate the sending keg, and give a quick pull on the receiving keg's PRV to reduce the pressure just enough to start the transfer. Any extra tips you have for the process?

 

[Bassman2003]

I have been studying O2 and its effects on beer for the past four years as a member of a certain group... The more I learn about it the more I am surprised at how difficult it is to keep out of everything. The mixing of gases appears to be instantaneous as well as happen though objects like the wrong kind of rubber used in seals etc... at a steady pace. Closed loop transfers are mainly as good as the weakest link in the setup - like unpurged lines or the oxygen that sneaks in when we put a QD over a post. You can work to minimize but getting rid of it all takes more effort. Remember that tank CO2 has O2 in it as well.

Your keg is the same a bottle for delivery and they measure O2 down to the parts per billion for packaging in larger berweries. You are aiming for the right technique as closed transfers are our best way but it still takes some time and practice to clean up your approach and make it as tight as possible.

 

[CyberFox]

I have been studying O2 and its effects on beer for the past four years as a member of a certain group... The more I learn about it the more I am surprised at how difficult it is to keep out of everything. The mixing of gases appears to be instantaneous as well as happen though objects like the wrong kind of rubber used in seals etc... at a steady pace. Closed loop transfers are mainly as good as the weakest link in the setup - like unpurged lines or the oxygen that sneaks in when we put a QD over a post. You can work to minimize but getting rid of it all takes more effort. Remember that tank CO2 has O2 in it as well.

Your keg is the same a bottle for delivery and they measure O2 down to the parts per billion for packaging in larger berweries. You are aiming for the right technique as closed transfers are our best way but it still takes some time and practice to clean up your approach and make it as tight as possible.

Yep, oxygen is pretty difficult to keep at bay. You can't rely on a CO2 blanket (since it's a myth) and even the regular silicone o-rings aren't the best for keeping out oxygen (seems like EDPM rubber is the way to go). I'll do whatever I can to keep out oxygen just short of it being a PITA. At the end of the day, as long as we put in a solid effort to keep out oxygen, we should end up with pretty good beer.

 

[gabrielrskin]

From my personal experience (nothing scientifical), the hop aroma loss is minimal. I usually purge my IPA kegs many times before transferring, then after they've been transferred, and then keep purging them even during forced carbing/after they're ready to be served, and although the purged gas smells delicious, the beer itself never seems to lose aroma due to that. Oxygen exposure, on the other hand, will definitely ruin your beer pretty quickly.

I do believe that's because most of hop oil compounds with desirable aroma, especially monoterpene alcohols and thiols, are quite solluble in water, and - despite popular belief - won't volatilize so easily. Hence dry hopping during active fermentation has become so popular and actually works, despite all the yeast CO2 activity dragging a small portion of that aroma away. It just seems a lot because it smells like all your hop aroma is being thrown away, but it's just not that much after all.