Hop aroma retention (or lack thereof) with pressure fermentation and transfer.

[rlprafa]

Hello everyone,

Not too long ago I started playing around with pressure fermentation and pressure transfers to an oxygen-less process (as much as possible for me, at least) and the beers are great.

I ferment in the all rounder, and when the fermentation is done, I remove the spunding valve prior to cold crashing and when it's time to transfer to the keg, I put some co2 and purge it a few times before connecting the hoses and everything else. In the gas side of the keg, I use a flow stopper with the spunding valve on top to control the pressure diference between vessels. I had a co2 bottle connected to the fermenter and kept it at 10 PSI while the keg had a bit less.

in my last batch I tried a pint right off the fermenter and it was the better hop aroma I've had in a non-IPA homebrew. I thought that would carry over to the keg, however a day later a poured myself another pint and for my surprise the hop aroma was gone.


I'm wondering what may have been my mistakes. Should I have a smaller pressure difference? or maybe set the spunding valve to a higher psi and not let any gas go out as I keep increasing the pressure in the fermenter?

I am not sure really what to do and my working theory is that the aroma was gone with the gas that went out by the spunding valve.

I am planning on brewing a NEIPA soon, and any help to fix that would be appreciated. Cheers.

 

[Elric]

If you are worried about losing aroma why not do a full closed transfer? Instead of off gasing the keg with a spunding valve, pressurize the keg to one or two psi less than your fermzilla and connect the gas in posts to each other. The pressure differential between the two will push the beer out of the fermzilla. It's best to have the fermzilla sitting higher than your keg so gravity can help the transfer. If transfer slows too much you can release a bit of gas in the keg with the prv to get it flowing again. This way you will not be losing any of your aromatics. try to make sure the keg is thoroughly purged before starting this though, as you will also not want to burp the keg after filling as this will just blow off the aromas you just worked so hard to keep.

 

[marc1]

I ferment in the all rounder, and when the fermentation is done, I remove the spunding valve prior to cold crashing and when it's time to transfer to the keg, I put some co2 and purge it a few times before connecting the hoses and everything else. In the gas side of the keg, I use a flow stopper with the spunding valve on top to control the pressure diference between vessels. I had a co2 bottle connected to the fermenter and kept it at 10 PSI while the keg had a bit less.

If that's the extent of purging your keg it could be part of your problem right there.

Here's a discussion of how much purging you need to get to negligible O2 levels:
https://www.homebrewtalk.com/threads/keg-purging-with-active-fermentation.628658/#post-8004741

Or it could need some more conditioning time. I find that beer changes a lot over the first couple weeks being kegged.

 

[rlprafa]

If you are worried about losing aroma why not do a full closed transfer? Instead of off gasing the keg with a spunding valve, pressurize the keg to one or two psi less than your fermzilla and connect the gas in posts to each other. The pressure differential between the two will push the beer out of the fermzilla. It's best to have the fermzilla sitting higher than your keg so gravity can help the transfer. If transfer slows too much you can release a bit of gas in the keg with the prv to get it flowing again. This way you will not be losing any of your aromatics. try to make sure the keg is thoroughly purged before starting this though, as you will also not want to burp the keg after filling as this will just blow off the aromas you just worked so hard to keep.

I guess I didn't tried a full closed because I assumed I'd have to keep bumping the pressure in the fermenter up because after a little while the pressure in the two vessels equalize and the transfer stops and I'd end up with 30 psi in the keg and having to purge it anyway. I'll admit that may have been a lazy approach. I should try and see.

 

[rlprafa]

If that's the extent of purging your keg it could be part of your problem right there.

Here's a discussion of how much purging you need to get to negligible O2 levels:
https://www.homebrewtalk.com/threads/keg-purging-with-active-fermentation.628658/#post-8004741

Or it could need some more conditioning time. I find that beer changes a lot over the first couple weeks being kegged.

Mind blowing! Thanks for sharing that.

Based on the discussion in that thread, I am definitely not purging it enough.

 

[marc1]

Mind blowing! Thanks for sharing that.

Based on the discussion in that thread, I am definitely not purging it enough.

If you are keeping it closed everywhere else, that might be worth looking at, especially for NEIPAs.

 

[Elric]

I guess I didn't tried a full closed because I assumed I'd have to keep bumping the pressure in the fermenter up because after a little while the pressure in the two vessels equalize and the transfer stops and I'd end up with 30 psi in the keg and having to purge it anyway. I'll admit that may have been a lazy approach. I should try and see.

I do it all the time. Like I said, if you also use gravity it should be fine and if need be you just release a small amount from the keg to pick up transfer rate again. You should not need to add any external gas to fully rack into the serving keg.

 

[rlprafa]

Pardon the mess in the pic. haha

Today I was racking another beer and this is what my racking setup look like.

The fermenter was at about 20psi (I forced carbonated after the fermentation as the thermo well fell off in the fermenter right after I closed the lid).

The keg was at about 13 to start with and I didn't do a fully closed transfer asI wanted to watch the pressure to understand (or try to) what was happening. I am either doing something very wrong here, or my first hunch was correct. The pressure between the two vessels equalize somewhat quickly and I am then left with two options:

1 - crank up the pressure in the fermenter
2 - release the pressure at the keg.

For this transfer, I did a combination of both. And neither was just a little. I had to release a lot of gas from the keg and pump a lot of gas into the fermenter.

I now know that I don't know how to do a closed transfer. So before doing a more hoppy forward beer where the hops would be wasted if I use the same technique I'll do some more studying.

From what you guys know, is there anything that seems absolutely wrong on what I am doing?

 

[marc1]

Pardon the mess in the pic. haha

Today I was racking another beer and this is what my racking setup look like.

The fermenter was at about 20psi (I forced carbonated after the fermentation as the thermo well fell off in the fermenter right after I closed the lid).

The keg was at about 13 to start with and I didn't do a fully closed transfer asI wanted to watch the pressure to understand (or try to) what was happening. I am either doing something very wrong here, or my first hunch was correct. The pressure between the two vessels equalize somewhat quickly and I am then left with two options:

1 - crank up the pressure in the fermenter
2 - release the pressure at the keg.

For this transfer, I did a combination of both. And neither was just a little. I had to release a lot of gas from the keg and pump a lot of gas into the fermenter.

I now know that I don't know how to do a closed transfer. So before doing a more hoppy forward beer where the hops would be wasted if I use the same technique I'll do some more studying.

From what you guys know, is there anything that seems absolutely wrong on what I am doing?

You should be OK without doing a closed loop, and just having the spunding valve on the gas port of your keg.

Let's confirm what you've got going on. It looks like:
-Beer coming out of the fermenter from the liquid post on top, and going into the liquid post of the keg.
-Gas coming out of the gas post of the keg, going through the auto-shutoff, then spunding valve, then ???? (open air?)

If you hook up gas to your fermenter and keep it at 20PSI, and keep the spunding at 15PSI, you should transfer fine.

I've never done a closed loop, but my understanding is that you would want them at about equal pressure. Liquid connected to fermenter and gas to the keg, with liquid and gas lines purged (run beer out the liquid, and gas out the gas). Then hook on the liquid connect to the keg and vent a little from the keg to get it started, then attach the gas to the fermenter at the gas post.

 

[rlprafa]

You should be OK without doing a closed loop, and just having the spunding valve on the gas port of your keg.

Let's confirm what you've got going on. It looks like:
-Beer coming out of the fermenter from the liquid post on top, and going into the liquid post of the keg.
-Gas coming out of the gas post of the keg, going through the auto-shutoff, then spunding valve, then ???? (open air?)

If you hook up gas to your fermenter and keep it at 20PSI, and keep the spunding at 15PSI, you should transfer fine.

I've never done a closed loop, but my understanding is that you would want them at about equal pressure. Liquid connected to fermenter and gas to the keg, with liquid and gas lines purged (run beer out the liquid, and gas out the gas). Then hook on the liquid connect to the keg and vent a little from the keg to get it started, then attach the gas to the fermenter at the gas post.

From the spunding valve it goes to a starsan filled bottle (the blue and orange thing in front of the fermenter).

If they are equal pressure, wouldn't the transfer stop? Unless there's some gravity siphoning going on that I can't see.

I think one good question to ask is: How long should I expect a fully closed transfer to go? It might be just a speed thing and I am too impatient to see the liquid going down. My transfers usually take anywhere between 15 and 30 minutes. Is that too short?

 

[marc1]

From the spunding valve it goes to a starsan filled bottle (the blue and orange thing in front of the fermenter).

If they are equal pressure, wouldn't the transfer stop? Unless there's some gravity siphoning going on that I can't see.

I think one good question to ask is: How long should I expect a fully closed transfer to go? It might be just a speed thing and I am too impatient to see the liquid going down. My transfers usually take anywhere between 15 and 30 minutes. Is that too short?

That's the theory behind the closed loop transfer. Once started, the beer transfers by gravity. Since everything is closed, you need the CO2 return to the fermenter to keep it going by gravity, otherwise the flow will stop because the pressure in the fermenter is decreasing and the pressure in the keg is increasing from the transferred beer.
I haven't done one, I just use CO2 to push the fermenter beer to the kegs, and have the kegs venting to the room.

 

[Jim R]

I would start purging your keg with fermentation CO2. I pressure ferment in my All Rounder (usually at just 12 psi or so) with my spunding valve on the fermenter. I then attach a Star San filled keg to the back side of the spunding valve with a hose to the gas line of the keg to force the fermentation CO2 into the keg. I have a hose from the beer line of the keg into a bucket to collect the kegs Star San as it slowly purges out during fermentation till the keg is empty (but now filled with fermentation CO2 and absolutely no O2).

Then when I do my closed transfer I put my CO2 tank onto my fermenter (at the same 12 psi as is in the fermenter during fermentation) and transfer the beer into the keg. I try to keep the pressure difference from the fermenter to the keg as small as possible (to minimize foaming with transfer). I raise the fermenter higher than the keg to use gravity also but I don't use a closed loop. I made a cheap spunding-type valve to attach to the gas side of the keg with a cheap push to fit plastic valve ($5 or so) with an attached small hose into a bottle of water or Star San. I could just use my spunding valve for this but I don't want to get any beer into it so this cheap plastic valve set-up prevents this. As I am making the transfer I can open this plastic valve just slightly till I see a little bubbling into this bottle of water as the keg CO2 is released. This probably maintains the keg pressure at 10-11 psi or so. I keep my keg on a small postal scale and stop the transfer when it reaches the weight that tells me the keg is full. Then I cold crash the keg and store it for sometimes for fairly long periods with no oxidation.

 

[Elric]

@marc1 has it right as to the issues you are encountering by not doing a closed loop and in that the closed loop relies a decent amount on gravity. If/when you decide to try a proper closed loop, you really only want –2psi less on your keg, not 7. Such a large difference will just blast the beer into the keg and potentially cause some excessive foaming in the keg.

 

[butterblum]

I'm wondering what may have been my mistakes. Should I have a smaller pressure difference? or maybe set the spunding valve to a higher psi and not let any gas go out as I keep increasing the pressure in the fermenter?

OP, were you ever able to sort this out?
I just started recapturing CO2 during fermentation and noticed that my samples straight out of the fermenter have been amazing, but are somewhat muted in the keg - even using closed pressure transfers.