Creating a CO2 loop during closed transfer

[ILMSTMF]

Hello,

I'm interested in using the CO2 "exhaust" from keg to feed back to FV during a closed transfer. My hopes are that
• I conserve my CO2 tank supply
• I can maintain a reasonably short transfer time

To the former, I think that's an obvious yes. But, am I wrong about the latter?

Current workflow
• purge keg of O2. Fill with StarSan, charge with tank CO2, push out a full pint of StarSan, purge the headspace, push out remaining StarSan. I don't capture the vented CO2 - that's a topic for another day.
• FV is Fermzilla. It contains beer that has had a head pressure of ~5psi while warm. That is from fermentation gas / no airlock attached after most of primary has "calmed down".
• FV gets crashed. As it cools, the beer is absorbing the CO2 from the headspace. Right? So, I'll put the tank supply on the FV post at 1psi just in case / to prevent implosion.
• Transfer day. The purged keg has about 10psi in it. The FV gets 11 or 12psi from the tank. Spunding valve attached to keg, set to 10psi. Transfer begins. At this point, I turn off the CO2 tank supply to the FV. As transfer will inevitably slow down, I reopen the supply until transfer gets moving again. I do this with the belief that it will reduce use of tank supply.
• Instead, once I get the transfer started, could I attach a line with QD from the out of the spunding valve to the gas post of the FV? Will I be able to move 5 gallons into keg in about 10 minutes?

Thank you in advance.

 

[Bobby_M]

Transfer begins. At this point, I turn off the CO2 tank supply to the FV. As transfer will inevitably slow down, I reopen the supply until transfer gets moving again. I do this with the belief that it will reduce use of tank supply.
• Instead, once I get the transfer started, could I attach a line with QD from the out of the spunding valve to the gas post of the FV? Will I be able to move 5 gallons into keg in about 10 minutes?

Without a constant supply into the FV, you're letting the pressure drop and you will get some CO2 breakout and the transfer will slow.

The only way to do a closed loop transfer, where the keg's vent feeds back to the FV is to have a gravity assist.

Thank you in advance.

 

[mashdar]

As Bobby said, you can do a closed gravity transfer with connected head spaces. Important: purged keg should have at least equal pressure to fermenter prior to starting, or transfer could blow up the yeast cake. (Don't ask me how I know this.)

• Set keg below fermenter
• Connect gas-gas line to keg
• Purge line
• Connect gas-gas line to fermenter (equalize)
• Connect liquid-liquid line to fermenter
• Purge liquid-liquid line
• Connect liquid-liquid line to keg
• Walk away
• Return later, note beer in gas-gas line, indicating keg is full to gas dip tube
• Drain some beer before/while hooking up to gas, or you risk back flow into gas lines.

Not listed: sanitation steps. If you're hand-purging, a spray bottle of star san is handy.

Purging is a big deal for O2 exposure, and also primes the liquid syphon.

 

[mac_1103]

The only way to do a closed loop transfer, where the keg's vent feeds back to the FV is to have a gravity assist.

And patience. If really short transfer time is your priority, you're probably going to be disappointed.

• Walk away
• Return later

 

[beren]

I can never get this to work. I transfer 1/3 or so then it stops. I start it again and it does not but stops again. In the end I just need to push with co2.

 

[Bobby_M]

I can never get this to work. I transfer 1/3 or so then it stops. I start it again and it does not but stops again. In the end I just need to push with co2.

As it transfers, the delta between liquid levels starts to drop so you don't get as much gravity assist. If you could get the fermenter a few more feet higher, it wouldn't stop. It's usually not convenient to do so and CO2 is cheap enough especially if you go with a 20LB tank.

 

[mac_1103]

I can never get this to work. I transfer 1/3 or so then it stops.

It always works for me. It is anything but fast, and keeps getting slower as it gets closer to the end. Is the bottom of your fermenter above the top of your keg?

 

[mac_1103]

If you could get the fermenter a few more feet higher, it wouldn't stop.

Yeah, every time I do a transfer I find myself wishing my jumpers were a couple of feet longer. One of these days I'm going to make myself a set of jumpers that are a couple of feet longer.

 

[beren]

Is the bottom of your fermenter above the top of your keg?

It is, but only just a little higher. Can’t easily raise it higher than that in the basement.

 

[mashdar]

My fermenter sits ~40" AFF to bottom in my upright fermentation freezer, so I just open the door and hook up the lines. If I had to move the fermenter I might reconsider, depending on the yeast involved.

 

[ILMSTMF]

The only way to do a closed loop transfer, where the keg's vent feeds back to the FV is to have a gravity assist.

Before we get too far, I don't think I'll be able to make it happen. A couple reasons.
Once FV is crashed, I don't want to move it 1) for concern of disrupting the yeast and 2) because I don't want to lug the heavy FV out.
Where it sits in the FC is where it stays during crash and transfer. I can't get it higher in the FC. The height difference between the liquid posts of the FV and keg might be 8"? Not sure if that matters - we really care about the difference between the heights of the beer in each container, right? ^^^

I mean...for the gravity assist, I wouldn't lay the keg on its side during transfer right?!?!

Purge liquid-liquid line

Actually, I do this by dispensing the first of the beer into hydrometer sample tube. Then I connect the liquid QD from FV to keg.

Purging is a big deal for O2 exposure, and also primes the liquid syphon.

...and that's why! ;-)

And patience. If really short transfer time is your priority, you're probably going to be disappointed.

I would like a definition for this, from anyone willing to answer please.
I transferred beer yesterday (not doing a closed loop). SWMBO asked how long it'd take and I estimated 10-15 minutes. I really should have checked the clock. When SWMBO visited later on with "10-15 huh?" 'Yeah, how long's it been?' "Probably a half hour!" I can't fathom...
Anyway. I don't expect it to take less than 10 minutes. But I sure would like for it to take only 10. Am I going about it the wrong way?

If you could get the fermenter a few more feet higher, it wouldn't stop. It's usually not convenient to do so and CO2 is cheap enough especially if you go with a 20LB tank.

Damnit if that doesn't strengthen the point I made! As for the tank, yeah, I would love to fit that in the FC but she only has the space for a 5#...and if I'm not conservative, it needs to be refilled more often than would be convenient. Filling my 20# (for keezer) is vastly more economical than filling the 5#!

Is the bottom of your fermenter above the top of your keg?

^^^
Yup, that's what I thought. ;-)

 

[mac_1103]

I would like a definition for this, from anyone willing to answer please.

My gravity assisted closed loop transfers take at least half an hour. Probably a good bit longer. I set them up and walk away. Do other stuff and come back to check. Walk away again. Etc. Etc. I don't time it because I'm not in any kind of rush and really don't care how long it takes.

 

[mac_1103]

Where it sits in the FC is where it stays during crash and transfer. I can't get it higher in the FC.

How big is your FC? Any chance you could raise the height of the whole thing?

 

[ILMSTMF]

I set them up and walk away.

Part of my problem is "what if the keg overflows?" I've had it happen before where the spunding valve got beer in it. I didn't enjoy cleaning that up...
Right, I suppose I could get a scale into the mix and figure out about how close to full / in danger of overfull it is.

Nevertheless, it sounds like I won't be able to save CO2 supply and time.

How big is your FC? Any chance you could raise the height of the whole thing?

It's a full size, standard one door fridge. In short, it will not be possible to lift it.
In long... it's in the garage / laundry room. A clothes rack is directly above it. Another fridge and chest freezer were recently moved around in the garage to accommodate my FC. The natives became restless... Making another modification in there will surely cause civil war! LMAO

 

[mac_1103]

Part of my problem is "what if the keg overflows?"

This. But if we're talking about a closed loop, overflow from the keg will just go back into the fermenter anyway. Or fill a two liter soda bottle with a carbonation tee before you start transferring to the keg so that you don't over fill it in the first place.

 

[ILMSTMF]

This.

Huh. I saw that a while ago but forgot about it since. Nice!

 

[Bobby_M]

Larger tubing ID definitely helps, but...
Consider that 28 inches of height differential (from the top of the FV liquid level to the top of the keg liquid level) is only ONE PSI of force. That's why an open loop transfer under even 2 psi would go twice as fast give or take. Even if the delta started at 28", by the time the FV is nearly empty and keg nearly full, that's more like ZERO PSI.

How much pressure can your FV handle? The higher you go, the faster the transfer.

 

[mashdar]

The other thing to consider with a closed transfer is that cleaning doesn't have to happen right away. The FV should still be pretty sanitary after transfer. So if it's easier, you can transfer Friday night during dinner, disconnect & walk away, then clean over the weekend.

Idea being, while the transfer took a while, you were doing other stuff for most of that time.

If doing forced transfer, I'd be tempted to get two of those float valves in series because I'm paranoid : ) And maybe set the keg in a water tight bucket.

 

[Broken Crow]

If you really want speed, there is another option. I chose this owing to disability, but even if I were able to lift my fermenters, I'd rather not disturb the trub:

The 1/4" ID EVABarrier can swag nicely onto the 3/8" barbs and I do my transfers with recieving keg sitting on a scale right next to the FV. These "12V RV water-pumps" can easily handle even already carbed beer and because they create their own output pressure foaming is dramatically reduced. (Not shown, is the gas-return line) I haven't actually timed it, but it takes well under 10 mins to fill a 5G keg.
Here's a link to a perfect pump:
https://www.brewhardware.com/product_p/supersucker.htm

 

[jerrylotto]

Like this...

 

[ILMSTMF]

How much pressure can your FV handle? The higher you go, the faster the transfer.

She's rated for... 35psi I think? Not that I'd want to put that much pressure on it.

I've about given up on the closed loop thing. Just going to stick with tank CO2 through the whole transfer.

Going off-topic...I'm not a genius so, please be patient. Tank CO2, head pressure into FV of, say, 15psi. On the keg, suppose I take spunding valve out of the equation. I can open the PRV and there will be an unrestricted transfer. But, the beer that's moving in is somewhat carbonated. So, that high pressure transfer is going to cause foaming in keg. Did I get that all right?
OK. Now, all of the above except, spund at 15 on the keg to equalize pressure between itself and the FV. Eliminates foaming in keg. But, does that (spunding at equal pressure) create a longer transfer time?

Thanks all!

 

[mashdar]

Beer will foam based on keg pressure vs equilibrium pressure of beer CO2 - if the beer is at steady state at 12psi, maintaining 12 psi at keg should prevent foaming*. Getting close will mostly prevent it.

Transfer rate will depend on the difference in pressure between the ends of the tube (including dip tubes). If you do 15psi headspace on both ends, you're doing a gravity transfer!

*assuming no temperature change. In reality, you'll get foaming from a warm keg.

 

[Bobby_M]

She's rated for... 35psi I think? Not that I'd want to put that much pressure on it.

I've about given up on the closed loop thing. Just going to stick with tank CO2 through the whole transfer.

Going off-topic...I'm not a genius so, please be patient. Tank CO2, head pressure into FV of, say, 15psi. On the keg, suppose I take spunding valve out of the equation. I can open the PRV and there will be an unrestricted transfer. But, the beer that's moving in is somewhat carbonated. So, that high pressure transfer is going to cause foaming in keg. Did I get that all right?
OK. Now, all of the above except, spund at 15 on the keg to equalize pressure between itself and the FV. Eliminates foaming in keg. But, does that (spunding at equal pressure) create a longer transfer time?

Thanks all!

It depends on how much carbonation you have. If you spund and create any signficant pressure above ambient, then you absolutely want to put some back pressure on the receiving keg. If the fermentation ends at something like 10psi, you want a 10psi PRV on the receiving keg's gas port and then you want to push about 15psi of pressure on the FV to make the transfer happen at a decent rate.

If the "some carbonation" is just some minimum residual stuff, don't worry about.

 

[ILMSTMF]

Excellent insight, @Bobby_M !

It depends on how much carbonation you have.

Is there an "easy way" to calculate that? I use this handy tool to estimate what to set head pressure to in order to achieve a target volume of carbonation.

http://kotmf.com/tools/forcecarb.php

...I just don't know how long it takes at a specific temperature to consider the beer carbonated to the target carbonation. Know what I'm saying?

 

[beren]

2 weeks is what’s generally said

 

[day_trippr]

2 weeks plus a few more days ime...

Cheers!

 

[mashdar]

It uses a bit more gas, but IMO if your FV can take it, throw 15psi on the keg and 20+ on the FV and it's not an issue. (Assuming you're not brewing a lambic or something, it's cold, and it's not horribly over-carbonated.)

("It" being foaming in the keg.)

 

[Bobby_M]

Excellent insight, @Bobby_M !


Is there an "easy way" to calculate that? I use this handy tool to estimate what to set head pressure to in order to achieve a target volume of carbonation.

http://kotmf.com/tools/forcecarb.php

...I just don't know how long it takes at a specific temperature to consider the beer carbonated to the target carbonation. Know what I'm saying?

The comments about 2 weeks are accurate if you're starting at no carbonation and apply chart pressure to the headspace.

If you're building up that head pressure by closing the fermenter and/or using a pressure release valve (spunding) during active fermentation, then it doesn't take any time. If you set a prv to 10 psi, and it builds up to that pressure and starts venting, you already have that level of carbonation in saturation.

 

[ILMSTMF]

If you're building up that head pressure by closing the fermenter and/or using a pressure release valve (spunding) during active fermentation, then it doesn't take any time. If you set a prv to 10 psi, and it builds up to that pressure and starts venting, you already have that level of carbonation in saturation.

Nailed it. Exactly the info I was hoping for.
That about sums up my process. Playing devil's advocate though - the pressure is built during primary fermentation, warm. Suppose 10psi is built up (no venting, spunding valve tells us the pressure it feels). When I crash temp, do I still have that level of carbonation in the beer? (Please excuse the noob questions). Thanks very much!

 

[mashdar]

The short answer is don't worry about it. The long answer is that the solubility increases faster than the headspace pressure drops, causing extra CO2 to slowly dissolve when you crash. How much, and how long it takes, depend on liquid:gas volumes and starting/ending temperature. But it's usually not a huge effect, and if you've got a gauge on it, matching gauge pressure is good enough.

 

[Bobby_M]

Nailed it. Exactly the info I was hoping for.
That about sums up my process. Playing devil's advocate though - the pressure is built during primary fermentation, warm. Suppose 10psi is built up (no venting, spunding valve tells us the pressure it feels). When I crash temp, do I still have that level of carbonation in the beer? (Please excuse the noob questions). Thanks very much!

Yes, use the chart to understand the concept. If you achieve 15 psi during fermentation at 65F, you have 1.7 volumes of CO2. As you cold crash the fermenter to 40F (assuming no external CO2 is connected), the 1.7 volumes will be maintained but the head pressure will drop to about 4psi. It's reasonable and customary to set your CO2 regulator to about 14 psi and attach it while you cold crash since you might as well pickup whatever additional carbonation you can in the meantime, but it's not critical to do so.