Spunding valve between the two kegs or at the end of the chain?

[kohalajohn]

Like many of us I use the fermentation co2 from the fermenting keg to purge the serving keg.

But where to place the spunding valve? Photo below shows how I currently do it. The spunding valve is in the middle, after the fermentation keg and before the serving keg. So the fermenting keg has 12 psi and the serving keg is ambient pressure. The serving keg runs co2 into a jar of sanitizer.

I think there are pros and cons each way.

The pro of my current way is that I have higher volume of gas flowing through the serving keg. The weight of gas produced is the same, but if I put the spunding valve at the end of the chain, then the serving keg would also be 12psi and the gas would be compressed, meaning less volume to flush out oxygen.

But now I am thinking of moving the spunding valve to the end of the chain, to the gas out port on the serving keg. It may make the closed transfer better. Both kegs would have equal pressure. And with lovely pure fermentation gas. I would not have to top up the serving keg with bottle co2.

Looking forward to your thoughts.

 

[kohalajohn]

Oh, the kegs in the photo are different sizes. But normally all the kegs are the same size. So go on that assumption.

 

[sibelman]

As I recall, @doug293cz's purging calculations assume that substantially all the gas flows through the serving keg. Your current setup keeps some of that gas in the fermenting beer. Moving the spunding valve to after the serving keg would further reduce the purge.

Perhaps Doug will estimate the effects of each, and the likely ppb of O2 in the serving keg after transfer. Or maybe he already has?

Of course, filling the serving keg will remove most of what's left there, either way, but residual O2 will soon equilibrate into the beer.

 

[kohalajohn]

That's right. I was just reading @doug293cz 's post on purging with fermentation gas. He puts a jumping line between the kegs, not a spunding valveven keeping the fermenting .

Having said that, even with the tank under pressure, the exit pipe is still hammering away for three to four days. Seems to be a lot of gas.

Since I want to ferment under pressure, I suppose the best answer is to put the spunding valve on the fermenting keg and use the remaining fermenting gas to push sanitizer through the serving keg.

 

[kohalajohn]

Actually he gives the answer here. I can still enjoy pressure in my fermenter, and still have enough left over gas to purge the serving keg. But only if the spunding valve is between the two kegs. It appears that I can't get too greedy and pressurize both kegs.

It is very interesting how the process varies depending on whether you are using gas or sanitizer.

Doug says:


There are a couple of ways to purge a keg with fermentation gas, depending on whether you start with a keg full of sanitizer, or an empty keg:

Starting with a keg full of sanitizer:

Connect the fermenter CO2 exhaust to the gas post of the keg, and connect a tube to the liquid post of the keg, and place the other end of the tube in a bucket to collect the sanitizer being forced out of the keg. Weight down the end of the tube in the sanitizer bucket so that it will stay submerged in the sanitizer and act as an air lock after the keg has emptied. If pressure fermenting the spunding valve should be placed between the fermenter and the keg.

Starting with an empty (but already sanitized) keg:

Connect the fermenter CO2 exhaust to the liquid post of the keg, and connect a blow-off tube or airlock to the gas post of the keg. If using a blow-off tube, the exit end should be submerged in sanitizer to form an airlock. This method of connecting the tubing forces the CO2 to flow upwards in the keg, helping to push air (and O2) up and out thru the gas post. The gas flow is then enough so that complete mixing of the CO2 and residual air is prevented, thus increasing the effectiveness of the purge (over the calculated worst case.) Again, if pressure fermenting the spunding valve should be placed between the fermenter and keg, as pushing lower pressure CO2 into the keg pushes more CO2 volume thru the keg, and the more volume "turn-overs" in the keg, the better the purging.

 

[sibelman]

If you use fermentation gas to push sanitizer out of your serving keg, you should be just fine, spunding or not, as there's almost no air (or oxygen) in the serving keg to begin with.

Doug's calculations (I found his massive post on this) are based on an empty, sanitized serving keg -- no spunding. Here is a thread about purging with spunding, but it doesn't include revision to the calculations to account for the reduced purging. However, the post you quoted seems to indicate that you can adequately purge an empty, sanitized keg even though considerable CO2 is retained in the pressure-fermented beer. But I don't recall seeing any numbers (i.e., ppb of oxygen) on this scenario.

Cheers!

 

[kohalajohn]

I think I have the answer. For me anyway.

Put a spunding valve on both kegs. The fermenting keg is set at 12 psi.

The serving keg has a valve set wide open and with a tube into a starsan jar

For the first two days of vigorous carbonation, purge the serving keg.

Then close the valve on the serving keg , to 12 psi. The eventual closed vessel transfer is balanced and will go well.

 

[mac_1103]

Why exactly do you want to pressurize the empty kegs anyway?

 

[kohalajohn]

Why exactly do you want to

Why exactly do you want to pressurize the empty kegs anyway?

Becasuse eventuallly I will be doing a closed transfer from the fermenting keg to the serving keg. It has been tried with a pressurized fermenting keg, and a non pressurized serving keg. When you connect the two kegs, the sudden rush to same pressure, causes the yeast cake to be violently disturbed. You have to stop, cold crash again and clarify again.

A second reason is that I don't want to pressurize the serving keg with a bottle. Bottled co2 contains some oxygen.

 

[mac_1103]

When you connect the two kegs, the sudden rush to same pressure, causes the yeast cake to be violently disturbed. You have to stop, cold crash again and clarify again.

Pull the PRV on the fermenter before you transfer.

A second reason is that I don't want to pressurize the serving keg with a bottle. Bottled co2 contains some oxygen.

How do you serve?

 

[kohalajohn]

Pull the PRV on the fermenter before you transfer.

How do you serve?

Have you tried pulling the PRV? It may be a solution, I just have not tried it yet. I may work great, but I imagine that even with the headspace depressurized, the liquid is still pressurized and would immediately start to reach equilibrium with the headspace and with the serving keg down below. It seems that equal pressure would make for a more gentle transfer.

But maybe I'll try it.

On the second point, yes, I do serve with bottled co2. But simply replacing the volume in the headspace as beer is drawn out, is a small amount of bottled co2 compared to using a bottle to dissolve 12ps in the whole body of the liquid beer.

Getting back to why I use fermentation gas to pressurize the serving keg, it's because it's there. It's free. It contains no oxygen. It makes for a more gentle closed transfer.

I'm going to have to eventually pressurize the serving keg anyway. I think the question is not why do I want to use fermentation gas to pressurize it, but why would I use bottle gas to pressurize it.

The only reason for using bottle gas, that I can think of, is that the fermentation keg can only produce enough gas to purge the serving keg and no more. And I don't know the answer to this yet. We'll figure it out.

If the fermenting keg has trouble producing enough gas to both purge and then pressurize the serving keg, that may be an argument for pushing a keg of starsan through the serving keg. You just have to push one volume through, instead of multiple volumes of gas.

 

[mac_1103]

the liquid is still pressurized and would immediately start to reach equilibrium with the headspace and with the serving keg down below

Yes, it will immediately start to equilibrate, but it would take a couple of weeks to actually reach equilibrium.

simply replacing the volume in the headspace as beer is drawn out, is a small amount of bottled co2 compared to using a bottle to dissolve 12ps in the whole body of the liquid beer

I didn't say that you shouldn't spund to carbonate the beer.

 

[sibelman]

sudden rush to same pressure

This can also be mitigated by slowly opening the transfer valve, but @mac_1103's PRV suggestion probably makes more sense. If you pull the PRV, I recommend you do so gently/gradually, thus reducing foaming in the fermenter. Might not be an issue if you have lots of head space.

 

[Broken Crow]

When beer is already pressurized and has to be transfered to the serving keg, my big concern is having the back-pressure to suppress foaming so I don't get a gallon of foam exiting the gas post on the receiving keg and gunking it up while throwing my measurements off. I always make sure the receiving keg starts 1-2psi higher than the feeder, connect the gas-return line first and then plug in the liquid line immediately after so that I don't get a keg 1/4 liquid and 3/4 foam....same process wether pushing with CO2, gravity or a racking pump.
That said; Is this a lager or IPA or one of the beers that actually benefits from pressure fermenting?
..just my 2-cents.

 

[rallenhall]

Before transferring from the fermenter to the purged serving keg, I add a bit of CO2 to each to ensure equilibrium. I don't want sudden bursts of decompression stirring things up in the fermenter, so control the transfer with a coupler/picnic tap on the serving keg gas post ... easier and more precise than pulling the PRV. Have not had issues with foam.

 

[kohalajohn]

Yes, it will immediately start to equilibrate, but it would take a couple of weeks to actually reach equilibrium.

I didn't say that you shouldn't spund to carbonate the beer.

Ah. I misunderstood.

 

[kohalajohn]

When beer is already pressurized and has to be transfered to the serving keg, my big concern is having the back-pressure to suppress foaming so I don't get a gallon of foam exiting the gas post on the receiving keg and gunking it up while throwing my measurements off. I always make sure the receiving keg starts 1-2psi higher than the feeder, connect the gas-return line first and then plug in the liquid line immediately after so that I don't get a keg 1/4 liquid and 3/4 foam....same process wether pushing with CO2, gravity or a racking pump.
That said; Is this a lager or IPA or one of the beers that actually benefits from pressure fermenting?
..just my 2-cents.

BC, rightly or wrongly, I'm pressure fermenting all of them, whether or not its a style that benefits from it.

It's probably my Scottish blood, but I like getting free co2. Having positive pressure keeps the gasket on my corny pressed up tight, even during cold crash.

 

[kohalajohn]

This morning I was very surprised at how much co2 is actually produced during fermentation. Last night I replaced the blow off hose on the serving keg with a spund valve and a blow off hose.

I guess the spund valve on the serving keg was pretty tight, as this morning the dials on the spunds for both kegs, were pinned past the maximum. It took ages to release enough co2 to get the dials back to a reasonable 12psi. The starsan jug was foaming up to overflowing as I released gas.

I think next time I'll fill keg #2, the serving keg, with starsan. I'll let the fermentation gas push the starsan through to keg #3, an empty keg.

Then I remove keg #3 from the system and put it away to be the serving keg in the next batch.

And then the first two kegs remain connected, same pressure, and each with a spund, ready for closed transfer. The second spund on the serving keg now runs a line into a starsan jug.

I'm sure this is all obvious to most of you, but it's a fun discovery for a beginner like me.

 

[mac_1103]

rightly or wrongly, I'm pressure fermenting all of them, whether or not its a style that benefits from it.

It's probably my Scottish blood, but I like getting free co2.

You don't have to pressure ferment to get the free CO2 and you can just spund the last few points to carbonate.

 

[Bobby_M]

You don't have to pressure ferment to get the free CO2 and you can just spund the last few points to carbonate.

Totally true and there are a lot of styles that objectively suffer from fermenting under pressure. English beers, Hefeweizens and most Belgians.

 

[Dland]

For what it's worth, I purge the two 5 gallon kegs I'm going to use for each batch with fermentation gas from conical fermentor. One keg at a time. For first half of fermentation I hook up one, after a few days, (or a week if a cold fermented lager that is going to take two weeks) I hook up the other keg.

Kegs are already sanitized and contain only air.

I do a trub dump and gravity test when fermentation is slowing down.

If getting close to expected gravity, I do a closed gravity fed transfer from fermentor to kegs, with low pressure CO2 feeding in from airlock port of to displace the beer as it leaves fermentor, so no air with 02 is sucked in.

I use a scale to tell when kegs are getting full, so I can leave a little head space at top.

I don't actually use an air lock, I have a tube that feeds down to a container of starsan. Most airlocks do not contain enough volume to be reliable after 5 gallon batches or so.

The fermentation process is finished in kegs, which I monitor with a pressure gauge. Beer is naturally carbonated by tail end of fermentation once in kegs. This is called spunding, but I have also heard that term used for low pressure fermentaion.

When I see that pressure has stopped rising in kegs, I know fermentation process is completely over, and yeast has cleaned up any diacytl and other unwanted fermentation by products.

Then I cold cash in keezer at around 32F.

Target pressure at cellar temp is around 30 PSI, which results in around 12 PSI at 32F. If pressure is higher than that once beer is cold crashed, I use the extra pressure to help dispense kegs that are already tapped.

Everyone is going to develop their own system after a while, but this has been serving me well for well over a hundred of batches of beer at this point.

If you have got this far in reading this, thanks for bearing with me. It just seems that sometimes fellow brewers make things more complicated than they need to be, and I like to share ideas to make things simpler. Hope this helps.

Feel free to ask if anyone has questions about this process.

 

[kohalajohn]

Totally true and there are a lot of styles that objectively suffer from fermenting under pressure. English beers, Hefeweizens and most Belgians.

There are some styles, some lagers, that do benefit though?

 

[Bobby_M]

There are some styles, some lagers, that do benefit though?

The theory is that you can ferment a lager on the warmer side under pressure with the benefit of faster fermentation while still suppressing the esters that a higher temperature would normally produce. You should still pitch on the higher side (number of cells) because pressure is one of the stress inputs for yeast.

Pressurized lager ferments is in lieu of proper temp control. If you're controlling temps down to lager temps, applying pressure during the whole ferment is counterproductive with no benefit.

 

[kohalajohn]

The theory is that you can ferment a lager on the warmer side under pressure with the benefit of faster fermentation while still suppressing the esters that a higher temperature would normally produce. You should still pitch on the higher side (number of cells) because pressure is one of the stress inputs for yeast.

Pressurized lager ferments is in lieu of proper temp control. If you're controlling temps down to lager temps, applying pressure during the whole ferment is counterproductive with no benefit.

Interesting. I do have temperature control.

If pressure is contraindicated during fermentation then surely it follows that we should not naturally carbonate. Why is it ok to naturally carbonate at the end but not the beginning?

It also makes we question why we have spunding valves.

Is it that some brewers feel the convenience of natural carbonation outweighs the negatives?

 

[Bobby_M]

Interesting. I do have temperature control.

If pressure is contraindicated during fermentation then surely it follows that we should not naturally carbonate. Why is it ok to naturally carbonate at the end but not the beginning?

It also makes we question why we have spunding valves.

Is it that some brewers feel the convenience of natural carbonation outweighs the negatives?

Spunding is happening at the back 5% of fermentation. It's the front 95% where we are setting the ester/phenol profile of the beer.

Pressure fermenting, which is a relatively new concept in homebrewing, is a similar but separate topic than spunding. You can build up enough pressure to naturally carbonate a beer by fermenting completely open and then set the spunding valve with a couple gravity points of attenuation remaining.

 

[kohalajohn]

Right. So I can still purge at the beginning. And still carbonate at the end.

And I think I still have my answer to the original question posted, which is that when I do add the spunging valve, I do it at the end of the daisy chain, so that both kegs are equally carbonated and I will have a gentle closed transfer.,

Actually, I start with the spunging valve attached, but wide open and hosed into a starsan jug. At the end of fermentation, I close the valve.

You don't pressurize kegs in the initial fermentation stage. You pressurize them later, to avoid vacuum suck back during the cold crash and then to make a good closed transfer.

Is this about right?