Using fermentation pressure to purge keg

[mggray87]

Maybe a dumb question but if I plan to purge 2 5g kegs during fermentation to save on CO2 tank. I sanitized both 5g kegs I dumped them out. Closed them up. Now do I want the CO2 to go down the dip tube beverage line and purge to the top. Or go into the in port and purge oxygen from bottom up?

I know there is a way to keep the first keg full to the top of starsan but I was confused with a bowtie how to chain two kegs and have the keg fill up to the top with the starsan before draining. I pictured the second one as soon as the pressure was up to bowtie pressure it would force the starsan out the dip tube before the second leg filled up?

 

[Clint Yeastwood]

Let's see.

I start with an empty keg and a keg full of Star San. The plan is to put CO2 in the Star San keg and then fill it with beer. To do this, I have to let the Star San push the air out of the empty keg.

Gas IN on Star San connected to CO2 bottle to let CO2 in. Liquid OUT on Star San keg to Liquid OUT on empty keg to move solution. Spunding valve connected to gas IN on empty keg to let air out.

CO2 goes from bottle to Star San keg, pushing solution up Star San keg's dip tube and into empty keg's OUT post. This fills empty keg with solution while CO2 fills Star San keg.

Air from empty keg goes out through spunding valve as solution fills it. I set the spunding valve maybe 4 psi lower than the CO2 bottle pressure to maintain movement while keeping it slow to prevent foaming. When the Star San keg starts pumping CO2 instead of solution, I disconnect. Then I invert the CO2-filled former Star San keg and let any remaining fluid out through the gas post.

Before using the keg which is now full of solution to purge a third keg, I top it off to get rid of excess air, and now I have test strips to make sure the solution is still okay to reuse.

Seems to work. I guess I should purge the headspace in the filled serving keg, since there will be a tiny amount of O2 in it. Not sure I've been doing that, but I try to use common sense, so maybe I have been.

 

[mac_1103]

If you're purging an empty keg, it's better to have the fermentation gas go in through the liquid post. If you're pushing liquid out of the keg, then the fermentation gas obviously has to go in through the gas post. The CO2 from fermenting a 5 gallon batch of 1.050 wort is very effective at purging one empty 5 gallon keg, but probably not two in series.

doug293cz's epic post on CO2 generation

 

[Clint Yeastwood]

Well, I totally misread the first post.

 

[mggray87]

If you're purging an empty keg, it's better to have the fermentation gas go in through the liquid post. If you're pushing liquid out of the keg, then the fermentation gas obviously has to go in through the gas post. The CO2 from fermenting a 5 gallon batch of 1.050 wort is very effective at purging one empty 5 gallon keg, but probably not two in series.

Oh so maybe do 1 at a time. Not chain them. That's good to know

 

[AlexKay]

I would think that if you connect the two kegs in series, both would purge almost exactly as well. Maybe it depends on the assumption of mixing (which doesn’t seem too strong anyway.) But I’d do it with no worries.

 

[khannon]

I would fill one keg with starsan(all the way), use fermentation to gas in on the keg, use liquid out to another keg's liquid out post. and put a spunding valve on the gas in post of the second set enough to let gas out. Wait for all the liquid to be in keg 2, then swap keg 2 into keg 1's place to push sanitizer out (adding more kegs as needed/wanted?). I don't think there is a great way to "Set it and forget it" past the first keg.

I do roughly this 1-2 times per year except with a CO2 cylinder, daisy chaining and swapping until I have all available kegs sanitized and pressurized. (35 kegs or so and you get a system and a rhythm, and a keg cleaning weekend..) but it means the rest of the times I get to "grab 2 fresh kegs" to package, so it's a rare case of past me not being such a jerk...

 

[Brew_Dude41]

So I have a question: if you are pushing sanitizer from a full keg to empty keg on a level surface using the liquid "in" posts, will a siphon start once the liquid starts flowing?

If so, would that create negative pressure in the fermenter until the kegs have equal volume and the pressure would build again to then push the liquid out of the keg being purged, or would the liquid only flow at the rate of CO2 production?

Just curious...

 

[mac_1103]

I would think that if you connect the two kegs in series, both would purge almost exactly as well. Maybe it depends on the assumption of mixing (which doesn’t seem too strong anyway.) But I’d do it with no worries.

I probably should have said maybe instead of probably, but I take Doug's word on all of this stuff, and he once said

If you string kegs together, then the flushed volume will be much higher, and the results less impressive.

but he later went on to say that two kegs would appear to give acceptable results.

 

[day_trippr]

fwiw, I do ten gallon batches, daisy-chain a pair of 5g kegs on the fermentation gas, and between the gas purging and adding 1 teaspoon of ascorbic acid in each keg just before filling I have been enjoying shelf life on my hazies like never before...

Cheers!

 

[DuncB]

Siphon can be an issue if you use a collapsible fermenter such as all rounder as the " ferment gas engine " and have one or two kegs that are positioned in a way to allow a siphon. You need a good head of pressure in the all rounder to replace the fluid volume movement. Be watchful.

 

[mggray87]

fwiw, I do ten gallon batches, daisy-chain a pair of 5g kegs on the fermentation gas, and between the gas purging and adding 1 teaspoon of ascorbic acid in each keg just before filling I have been enjoying shelf life on my hazies like never before...

Cheers!

I'll get my feet wet and do a single keg first. Let me dip the toes first!

 

[jerrylotto]

I leave a few cups of sanitizer in each keg and daisy chain them with fermentation gas going in the liquid post and an bubbler on the last keg gas post. The first keg on the line gets used first after I blow out the last little bit of sanitizer through the liquid post and I keep the keg order for my next batch by adding one to the end. Typically there are two or three in line

 

[balrog]

I don't believe you need to push sanitizer out with ferment gas.
Just hook up the ferment gas to liquid side, hook gas side to tub into blowoff jar.
There's enough CO2 produced by 5gal batch to sufficiently de-oxygenate a 5gal keg.

 

[DuncB]

Reading link in post 3 explains it all, marginal gain of pushing sanitiser out with ferment gas. I'm happy to go for that marginal gain.