Closed-circuit Fermentor-to-Keg Transfer

[day_trippr]

fwiw, I started a pair of hopped-up fermentors cold-crashing this morning, thought I'd document the results.

Took a picture of the hoppier vessel at the start with the beer temp at ~68°F,
then a couple of hours or so later when the beer had dropped to ~58°F,
then an hour later when the beer had dropped to 55°F.
Nearly all of the hoppy sludge had dropped already...

Cheers!

 

[mongoose33]

This is an impossibility for me due to my liquid-out tubes being cut about an inch above the bottom of the keg. I fear that I'd leave too much sanitizer at the bottom of my keg and it would water-down or create a strange flavor within my beer.

Today I kegged 5 gallons from my ssBrewTech Chronical. I did a closed-circuit transfer from the sample port and put the conical under CO2 pressure. Since I've had issues with hop trub getting stuck within the QD OUT and the OUTpost, I removed the internal components of both QD and OUTpost and the beer flowed quickly and seamlessly. Sure, once I filled the keg I had to unscrew the OUTpost to reassemble the internal components, but I'm assuming that there was minimal oxygen exposure from that space during the reassemble. Furthermore, the only volume of the beer exposed to oxygen was maintained within liquid-out tube. I can't see that oxygen-exposed volume escaping to oxygenate the rest of the beer. I'll let you know how the beer turns out. Does anyone see any issues/flaws with this method???

When I use my Torpedo kegs, a cup or thereabouts of Star-San is left in the keg after I've driven out the Star-San with CO2 in order to clear the keg of O2. I don't want that in my beer either, so I pop the lid, turn the keg upside down over the sink, and let that liquid out. There must be a little air replacing that Star-San, but it's minimal--just about, I imagine, what what you get when you reassemble your out posts.

I have very little Star-San left in my soda kegs by comparison, but I usually invert them to dump out whatever is in there anyway.

With a little purging after the beer is transferred, I just can't imagine I'm getting much if any noticeable oxidation. I don't taste it in my kegged beers, which tells me what I'm doing is sufficient.

 

[schematix]

"A volume of air smaller than would fill a shot glass, if
trapped in the keg, contains enough oxygen to raise the dissolved oxygen level
of a 20 liter batch of beer by more than 0.2 ppm. With a dissolved oxygen
level of 0.8 ppm, the fresh flavor of the beer fades within a week, even at cold
temperatures." -- http://www.germanbrewing.net/docs/Brewing-Bavarian-Helles.pdf

 

[oakbarn]

Just use a bag and more hops. I destroyed a March Pump by not using bags. I do not fly sparge, I add extra grain. I do not free float the hops,I use a bag and extra hops. I also fill the cornys with CO2 then free flow through the lid using a Dave's Rag ( A rag soaked in Star San) to cover the top.

 

[schematix]

I destroyed a March Pump by not using bags.

Can you elaborate on what happened to your pump?

 

[mongoose33]

"A volume of air smaller than would fill a shot glass, if
trapped in the keg, contains enough oxygen to raise the dissolved oxygen level
of a 20 liter batch of beer by more than 0.2 ppm. With a dissolved oxygen
level of 0.8 ppm, the fresh flavor of the beer fades within a week, even at cold
temperatures." -- http://www.germanbrewing.net/docs/Brewing-Bavarian-Helles.pdf

I appreciate the reference. I guess what I'm missing is why I can't seem to taste the oxidation.

I know that whole German PDF thread is about the dangers of oxidation, but if it truly was such a terrible, awful thing, then how on earth are people producing delicious homebrews, people who aren't taking as much care in avoiding oxidation as the Germans apparently are doing?

 

[day_trippr]

"It's a mystery"

Oxidation is a moving process - depending on where you catch it, its appearance may differ.

Classically, it'll start by the all-too-rapid attenuation of aroma characters, proceed to an untoward sweetness, and finish with the dreaded sherry-heading-towards-cardboard phenomenon. All moderated by time and degree of O2 exposure, of course.

There've been a hella lot of threads started in kegging forums regarding the hop aroma attenuation thing, and almost without fail all paths lead to oxidation. Which shouldn't be surprising - what the heck else could cause many ounces of aroma hops to disappear??

Cheers!

 

[Gustatorian]

When I use my Torpedo kegs, a cup or thereabouts of Star-San is left in the keg after I've driven out the Star-San with CO2 in order to clear the keg of O2. I don't want that in my beer either, so I pop the lid, turn the keg upside down over the sink, and let that liquid out. There must be a little air replacing that Star-San, but it's minimal--just about, I imagine, what what you get when you reassemble your out posts.

I have very little Star-San left in my soda kegs by comparison, but I usually invert them to dump out whatever is in there anyway.

With a little purging after the beer is transferred, I just can't imagine I'm getting much if any noticeable oxidation. I don't taste it in my kegged beers, which tells me what I'm doing is sufficient.

How do you like those Torpedo kegs? Can you tell me more about them?

In addition to the fill with water/sanitizer-then force it out with CO2 method, this obviously won't work if I'm dry-hopping in the keg. Also, maybe another way to get the residual Star-San from the keg would be to just open the PRV and let it out from there? Obviously that would let in air too.

I'm thinking that replacing the components of my OUTpost would let in much less air then opening the top due to the small amount of surface area exposed to the air when the OUTpost is removed. Additionally, the volume exposed to oxygen is contained within the dip tube. Again, if anyone sees flaws with that, LMK!

 

[mongoose33]

How do you like those Torpedo kegs? Can you tell me more about them?

In addition to the fill with water/sanitizer-then force it out with CO2 method, this obviously won't work if I'm dry-hopping in the keg. Also, maybe another way to get the residual Star-San from the keg would be to just open the PRV and let it out from there? Obviously that would let in air too.

I'm thinking that replacing the components of my OUTpost would let in much less air then opening the top due to the small amount of surface area exposed to the air when the OUTpost is removed. Additionally, the volume exposed to oxygen is contained within the dip tube. Again, if anyone sees flaws with that, LMK!

I think they're great.

They work the same as a normal corny keg. They have no rubber on the base or comprising the handles, so I'm not getting black marks all over whatever. I also like that the kegs weigh less than the corny kegs which is helpful when hefting one over the collar of the keezer.

They have two versions--a shorter fatter version, and a taller, skinnier version. They also come in small, medium and large capacities. I have the large and small ones. Taking the small one (filled of course) to a party this weekend.

As far as the displace star-san w/ CO2 thing, why wouldn't it work with dry hopping? Isn't your keg empty regardless how you do it?

 

[Gustatorian]

I think they're great.

They work the same as a normal corny keg. They have no rubber on the base or comprising the handles, so I'm not getting black marks all over whatever. I also like that the kegs weigh less than the corny kegs which is helpful when hefting one over the collar of the keezer.

They have two versions--a shorter fatter version, and a taller, skinnier version. They also come in small, medium and large capacities. I have the large and small ones. Taking the small one (filled of course) to a party this weekend.

As far as the displace star-san w/ CO2 thing, why wouldn't it work with dry hopping? Isn't your keg empty regardless how you do it?

Will the posts for the torpedo work with standard CO2/Liquid QDs?

Regarding Dry-Hopping: You'll displace all that liquid with CO2, but you're going to have to open the top to pour hops in regardless - exposing the inside to air. I think the process of replacing liquid volume with CO2 volume is a solid procedure to assure that most oxygen is out of the keg, and potentially would work for me if a) my liquid dip tubes reached the bottom of my keg and could take out all of the sanitizer and b) if I wasn't dry-hopping my beer.

 

[mongoose33]

Will the posts for the torpedo work with standard CO2/Liquid QDs?

Yes--it's a standard corny keg except no rubber.

Regarding Dry-Hopping: You'll displace all that liquid with CO2, but you're going to have to open the top to pour hops in regardless - exposing the inside to air. I think the process of replacing liquid volume with CO2 volume is a solid procedure to assure that most oxygen is out of the keg, and potentially would work for me if a) my liquid dip tubes reached the bottom of my keg and could take out all of the sanitizer and b) if I wasn't dry-hopping my beer.

There will be a certain amount of oxygen that attaches to the hops unless you're pouring directly from a nitrogen-flushed package--and even then, at least some will come in.

But think about this: as you pour *anything* into the keg, it's displacing the CO2 left behind. Maybe some O2 comes in with whatever you're pouring in, but you're pushing C)2 out as you pour anything in--which creates a positive OUT pressure.

Dry hopping should work fine with this. And the Torpedoes? Standard Corny Kegs, except improved. I'd get more. I recently bought 5 standard (rubber) corny kegs for $250, in great shape; I couldn't pass that up, I needed some more kegs. But if they were Torpedoes, I'd be even happier.

 

[doug293cz]

...

But think about this: as you pour *anything* into the keg, it's displacing the CO2 left behind. Maybe some O2 comes in with whatever you're pouring in, but you're pushing C)2 out as you pour anything in--which creates a positive OUT pressure.

...

As soon as you open the keg lid after a liquid purge, air starts mixing with the CO2 in the keg (CO2 "blankets" are a myth.) Whatever you add next won't come near to displacing enough gas to get out all the O2 you let in. You can still get the O2 out by doing multiple purges after filling the keg, but there no way to know how many purges you need without an O2 meter. So, you have to do extra purges just to be safe. Also, if your CO2 supply has more than 0.1 - 0.2 ppm O2, then you can't get enough O2 out, no mater what you do.

Brew on

 

[schematix]

Also, if your CO2 supply has more than 0.1 - 0.2 ppm O2, then you can't get enough O2 out, no mater what you do.

Brew on

Why did you have to go and open that can of worms???

Great point though. So who knows where to buy an O2 scrubber for a kegging system?

 

[AF1HomeBrew]

Great discussion here. I've been thinking about how I could do this for the last few months, and I am amazed that someone hasn't created a Kickstarter product to deal with this LOL. Anyway I think the next time I brew I might configure one of my SS Brewtech buckets with a Clear Draught system (http://www.clearbeerdraughtsystem.com/) and try transferring from my Brew Bucket to a keg to see how it works. This would transfer the beer from the fermentor from the top down.

Wish I would have thought of the "Dave's Rag" when I transferred my Vienna Lager back in April.

Pics from a Vienna Lager I brewed back in April. The Clear Draught system is installed in the kegs that I lagered the beer in.

 

[oakbarn]

I use the 1/4 inch type ball lock connectors. I just screw on a black one to purge my Corneys of oxygen. I normally empty the kegs of star san then fill with CO2 through the beer out. The top is covered with a Dave Rag (Star San Soaked Rag) and then I just put the hose from the conical into the keg and fill. I use the Dave rag to wipe off the hose as it is going in. I would say that O2 is not an issue this way as some beers are months in the keg without issues.

 

[oakbarn]

As soon as you open the keg lid after a liquid purge, air starts mixing with the CO2 in the keg (CO2 "blankets" are a myth.) Whatever you add next won't come near to displacing enough gas to get out all the O2 you let in. You can still get the O2 out by doing multiple purges after filling the keg, but there no way to know how many purges you need without an O2 meter. So, you have to do extra purges just to be safe. Also, if your CO2 supply has more than 0.1 - 0.2 ppm O2, then you can't get enough O2 out, no mater what you do.

Brew on

In a confined space, you can create a Blanket of CO2. As far as air mixing when you open the lid, that is true but the bottom of the keg is still full of CO2. 0.1 to 0.2 PPM is an insignificant amount of O2 compared to the 99.9 to 99.8 PPM of CO2. Grain Silos where there is a natural CO2 "blanket", require breathing equipment to enter. You can create a visual blanket with some Dry Ice and water. The CO2 will evaporate and cover the water in a fog. Sure, it goes away, but if you did it in an enclosed contained, it would take a long time.

 

[jddevinn]

In a confined space, you can create a Blanket of CO2. As far as air mixing when you open the lid, that is true but the bottom of the keg is still full of CO2. 0.1 to 0.2 PPM is an insignificant amount of O2 compared to the 99.9 to 99.8 PPM of CO2. Grain Silos where there is a natural CO2 "blanket", require breathing equipment to enter. You can create a visual blanket with some Dry Ice and water. The CO2 will evaporate and cover the water in a fog. Sure, it goes away, but if you did it in an enclosed contained, it would take a long time.

Sorry but 0.2ppm is NOT an insignificant amount of O2 according to all published brewing literature.

Like an active fermentation dry Ice is a continuous supply of CO2. The stratification between gasses observed is mostly due to temperature differences.

If by a "Long Time" you mean less than a minute to be WAY above 1ppm then yes.

 

[TexasWine]

When I use my Torpedo kegs, a cup or thereabouts of Star-San is left in the keg after I've driven out the Star-San with CO2 in order to clear the keg of O2. I don't want that in my beer either, so I pop the lid, turn the keg upside down over the sink, and let that liquid out.

Why not just turn the keg upside down and pull the PRV to push out that last little bit of Star San?

 

[doug293cz]

Why not just turn the keg upside down and pull the PRV to push out that last little bit of Star San?

Even if you do that, you still have about 3 fl oz of liquid trapped because of the lid design.





Brew on

 

[TexasWine]

Even if you do that, you still have about 3 fl oz of liquid trapped because of the lid design.

View attachment 360548

View attachment 360549

Brew on

Hmm. Shorten the gas post, tilt the keg a smidgen, press in the poppet?

 

[Gustatorian]

Sorry but 0.2ppm is NOT an insignificant amount of O2 according to all published brewing literature.

Like an active fermentation dry Ice is a continuous supply of CO2. The stratification between gasses observed is mostly due to temperature differences.

If by a "Long Time" you mean less than a minute to be WAY above 1ppm then yes.

Mind linking any of this literature?

 

[doug293cz]

Mind linking any of this literature?

Here's my favorite: http://www.craftbrewersconference.com/wp-content/uploads/2015_presentations/F1540_Darron_Welch.pdf. Look at page 21.

Brew on

 

[doug293cz]

In a confined space, you can create a Blanket of CO2. As far as air mixing when you open the lid, that is true but the bottom of the keg is still full of CO2. 0.1 to 0.2 PPM is an insignificant amount of O2 compared to the 99.9 to 99.8 PPM of CO2. Grain Silos where there is a natural CO2 "blanket", require breathing equipment to enter. You can create a visual blanket with some Dry Ice and water. The CO2 will evaporate and cover the water in a fog. Sure, it goes away, but if you did it in an enclosed contained, it would take a long time.

You can only have a stable blanket (that lasts for more than a few minutes) if you have a continuous source of CO2 generation. The thickness of the blanket will depend on the rate of CO2 generation vs. the rate of air/CO2 inter diffusion. With dry ice and water, what you see is water fog (made up of small water droplets.) CO2 is invisible, just like air. Check the "enclosed container" in this video. Takes only about 30 minutes for Br2, which is 3.6 times heavier than CO2, to completely mix in a totally enclosed system. CO2 is about the same density as the NO2 shown later in the video, which mixes much faster than the Br2.

[ame]https://www.youtube.com/watch?v=_oLPBnhOCjM[/ame]

OSHA requires breathing equipment when the O2 content of the local atmosphere is less than 19.5% (vs. 21% normally). So, that is a meaningless comparison. Likewise, allowable long term exposure limits for humans to CO2 is 0.5%, and max short term limit is 3%, and both are easily exceeded in an enclosed fermentation area. So, too much CO2 for breathing is another meaningless comparison.

Even if you replace 99.9% of the air with CO2 you still have 0.1% air (10,000 ppm) and 0.021% O2 (2,100 ppm.) That's still about 20,000 times too much O2. It doesn't take much O2 to degrade the flavor of beer over time. See page 21 of http://www.craftbrewersconference.com/wp-content/uploads/2015_presentations/F1540_Darron_Welch.pdf.

Brew on

 

[TexasWine]

You can only have a stable blanket (that lasts for more than a few minutes) if you have a continuous source of CO2 generation. The thickness of the blanket will depend on the rate of CO2 generation vs. the rate of air/CO2 inter diffusion. With dry ice and water, what you see is water fog (made up of small water droplets.) CO2 is invisible, just like air. Check the "enclosed container" in this video. Takes only about 30 minutes for Br2, which is 3.6 times heavier than CO2, to completely mix in a totally enclosed system. CO2 is about the same density as the NO2 shown later in the video, which mixes much faster than the Br2.

https://www.youtube.com/watch?v=_oLPBnhOCjM

OSHA requires breathing equipment when the O2 content of the local atmosphere is less than 19.5% (vs. 21% normally). So, that is a meaningless comparison. Likewise, allowable long term exposure limits for humans to CO2 is 0.5%, and max short term limit is 3%, and both are easily exceeded in an enclosed fermentation area. So, too much CO2 for breathing is another meaningless comparison.

Even if you replace 99.9% of the air with CO2 you still have 0.1% air (10,000 ppm) and 0.021% O2 (2,100 ppm.) That's still about 20,000 times too much O2. It doesn't take much O2 to degrade the flavor of beer over time. See page 21 of http://www.craftbrewersconference.com/wp-content/uploads/2015_presentations/F1540_Darron_Welch.pdf.

Brew on

This is exactly why I love Doug's posts.

 

[Carlscan26]

Even if you do that, you still have about 3 fl oz of liquid trapped because of the lid design.



View attachment 360548



View attachment 360549



Brew on

That's still far less than not flipping it over. Also if you leave it attached to the CO2 and shake it around I'd imagine you could get another ounce or two out...especially if you stop and let pressure build up before you open the PRV. Also, I doubt that 1-3 oz of starsan would make any noticeable difference in a five gallon batch of beer.

 

[doug293cz]

That's still far less than not flipping it over. ...

Did you measure this? If not, how do you know?

... Also, I doubt that 1-3 oz of starsan would make any noticeable difference in a five gallon batch of beer.

I agree with you on this.

Brew on

 

[Carlscan26]

Did you measure this? If not, how do you know?

I'm not going to cut any of my dip tubes to be 1" from the bottom of the keg but it's reasonable to assume that the remaining volume is definitely more than 3 oz right?

This is an impossibility for me due to my liquid-out tubes being cut about an inch above the bottom of the keg. I fear that I'd leave too much sanitizer at the bottom of my keg and it would water-down or create a strange flavor within my beer.

 

[doug293cz]

I'm not going to cut any of my dip tubes to be 1" from the bottom of the keg but it's reasonable to assume that the remaining volume is definitely more than 3 oz right?

For a dip tube cut 1" from the bottom, yes (I didn't realize you were talking about that case.) For an unmodified dip tube, I'm not so sure.

Brew on

 

[day_trippr]

If an unmodified oem dip tube is properly positioned in the small well at the bottom of the keg, it's only going to leave a couple of tablespoons of fluid (if that) when totally blown out...

Cheers!

 

[jddevinn]

Mind linking any of this literature?

Gustatorian,

The majority of the literature I am talking about is not available for linking as they are physical textbooks.

• Technology Brewing and Malting, Kunze
• A Textbook of Brewing, J. DE CLERCK
• Brewing Science and Practice
• The Role of Oxygen in the Brewery (this one is a link) http://www.ibdlearningzone.org.uk/article/search/?searchstring=yeast&category=22&author=&keyword=
  
  These books give both recommendations and chemical reasons for the changes due to oxygen.
  
  From Brewing Science and Practice
  
  Preventing air getting into the beer [during packaging} is essential. All the precautions followed in producing bright beer must be maintained. The final product specification for dissolved oxygen in teh beer will be <0.2mg/l [same as 0.2ppm], in some cases, <0.1mg/l, so during filling operations the pickup of oxygen must not exceed 0.02-0.03mg/l [0.02-0.03ppm]. if this oxygen level is not achieved serious flavour deterioration will result.
  
  ...
  
  Roughly 1 ml of air in a 300ml bottle will give an oxygen content of 1ppm, wich is probably enough to oxidize all the reductiones present in a light lager beer.
  

 

[Braufessor]

Just listened to one of the 2016 conference seminars on oxidation...... if you think it is depressing trying to figure out how to eliminate oxygen pick up transferring from fermenter to keg.... Give this a listen (if you can access it without being an AHA member???). You will be ready to give up entirely.

He talks about the impact of oxidation at every phase. The most depressing part is when he talks about the introduction of oxygen during the mash and the fact that enough oxygen is introduced in standard mashing processes to be well over the threshold. Big production breweries are actually going to nitrogen flushed mash tuns.

At that point I just thought.... well, that is never going to happen on the homebrew level.

https://www.homebrewersassociation....on16 - Identifying and Avoiding Oxidation.mp3

To be honest, while I acknowledge that the "industry standard" for oxygen in beer is very, very low. I don't think there are any home brewers achieving that over the course of their entire process. And, if some are, it is a tiny, tiny piece of a single percentage.

I would be curious if at some point there is simply a threshold that is above industry standard, but below what 90%+ beer drinkers can ever really notice as a detrimental effect in their beer. Basically, if no one can taste a certain level of a "problem", is it actually a problem?

With that said, everyone should take as much care as they can not to introduce oxygen - especially at the points they can control. I like the tip someone mentioned about turning the keg upside down and venting out the CO2 post to get the last bit of star san out in a keg with a short tube (I use one for dry hopping sometimes). Filling the keg with star san and pushing out with CO2 is absolutely the way to go - simple, efficient, effective.

 

[user 141939]

Maybe this is a dumb question. If you're filling a closed keg through the liguid out, how do you know when to stop? Since you can't see the level at all.

 

[TexasWine]

Maybe this is a dumb question. If you're filling a closed keg through the liguid out, how do you know when to stop? Since you can't see the level at all.

Well, you could use one of these.

https://www.ballandkeg.com/

Or, what I started doing was putting a known amount of wort in the fermenter and leaving a known amount behind. I'll put 5.5 gallons in, and I know where to set my rotating dip tube to have exactly 0.75 gallons left behind. 4.75 gallons to the fermenter every time.

 

[jddevinn]

Maybe this is a dumb question. If you're filling a closed keg through the liguid out, how do you know when to stop? Since you can't see the level at all.

I fill the kegs off the fermenter at the same time using a manifold. Once the beer starts coming out of the PRV (with NPT fitting and hose barb) or the gas out (that has a QDC) I pull the QDC off of that keg.

 

[doug293cz]

Maybe this is a dumb question. If you're filling a closed keg through the liguid out, how do you know when to stop? Since you can't see the level at all.

If you are transferring cold beer to the keg, you can just watch the condensation line on the outside of the keg (might not work so well during winter if outside or in unheated garage, or if the humidity is very low.)

Brew on

 

[vance]

Just listened to one of the 2016 conference seminars on oxidation...... if you think it is depressing trying to figure out how to eliminate oxygen pick up transferring from fermenter to keg.... Give this a listen (if you can access it without being an AHA member???). You will be ready to give up entirely.

He talks about the impact of oxidation at every phase. The most depressing part is when he talks about the introduction of oxygen during the mash and the fact that enough oxygen is introduced in standard mashing processes to be well over the threshold. Big production breweries are actually going to nitrogen flushed mash tuns.

At that point I just thought.... well, that is never going to happen on the homebrew level.

https://www.homebrewersassociation....on16 - Identifying and Avoiding Oxidation.mp3

To be honest, while I acknowledge that the "industry standard" for oxygen in beer is very, very low. I don't think there are any home brewers achieving that over the course of their entire process. And, if some are, it is a tiny, tiny piece of a single percentage.

I would be curious if at some point there is simply a threshold that is above industry standard, but below what 90%+ beer drinkers can ever really notice as a detrimental effect in their beer. Basically, if no one can taste a certain level of a "problem", is it actually a problem?

With that said, everyone should take as much care as they can not to introduce oxygen - especially at the points they can control. I like the tip someone mentioned about turning the keg upside down and venting out the CO2 post to get the last bit of star san out in a keg with a short tube (I use one for dry hopping sometimes). Filling the keg with star san and pushing out with CO2 is absolutely the way to go - simple, efficient, effective.

I thought oxygen during mashing was a good thing?

 

[mongoose33]

I fill the kegs off the fermenter at the same time using a manifold. Once the beer starts coming out of the PRV (with NPT fitting and hose barb) or the gas out (that has a QDC) I pull the QDC off of that keg.

That must leave almost no headspace--how easy or how long is it to carbonate something like that?

 

[mongoose33]

If you are transferring cold beer to the keg, you can just watch the condensation line on the outside of the keg (might not work so well during winter if outside or in unheated garage, or if the humidity is very low.)

Brew on

I racked (closed circuit) to a keg last night, and that's exactly what I did--watched the rising condensation line on the keg.

 

[jddevinn]

That must leave almost no headspace--how easy or how long is it to carbonate something like that?

Depending on the method I'm using:

1. My "default" carbing method is to use a keg with an additional QDC added to the middle of the lid. Carb stone is attached to this QDC and carbing is done in 2-3 days, headspace doesn't matter I then transfer to another keg to serve.
2. IF I want to force carb "normally" I'll put pressure on the keg then hook a picnic tap to the gas in and pour beer out (or more realistically drink) down to the bottom of the gas in pickup. Oversizing batches by a gallon or two helps still end up with full kegs.
3. I've started experimenting with natural carbing with a spunding valve. In this case headspace doesn't matter.

 

[jddevinn]

I also remembered back when I used to fill one keg at a time I'd calculate the weight of 5 gallons of that gravity beer, place the keg on my grain scale, tare and then fill until I got the weight of 5 gallons before switching kegs.