Carbonating half full kegs

A forum to discuss the various ways of getting beer into your glass.
Post Reply
HopIt

Carbonating half full kegs

Post by HopIt » Fri Jan 12, 2018 9:54 am

If you have 2 corny kegs, and fill both up to 13 litres, there will be quite a lots of headspace and therefore space for co2. If you pressurise to 30 or 40 psi, and remove from the gas, will they carbonate? How would this differ from fully filling a keg, going to 30/40 psi, and leaving connected to the gas for the desired amount of time?

McMullan
Drunk as a Skunk
Posts: 825
Joined: Tue Jul 14, 2015 7:48 pm
Location: Here

Re: Carbonating half full kegs

Post by McMullan » Fri Jan 12, 2018 11:51 am

You'd have to get a refill more often, I guess.

Jambo
Hollow Legs
Posts: 375
Joined: Wed Jul 30, 2008 2:00 pm
Location: Aberdeenshire

Re: Carbonating half full kegs

Post by Jambo » Fri Jan 12, 2018 1:26 pm

Other thing to bear in mind with that sort of headspace is the importance of burping the keg to displace oxygen.

To answer your question, they will carbonate but not sure to what level and don't know off the top of my head how to calculate it... You'll have 6L of CO2 at 40 psi initially and 13 L of beer. Over time this CO2 will dissolve into the beer until an equilibrium is reached and you'll have some level of carbonation and 6L of CO2 at some lower pressure. What 'some' means in both cases is what you need to figure out, it can be calculated if you know how, and it is (highly) temperature dependent.

I think most Cornies can take up to 100 psi so as long as you work it out you can probably get this to work. But it's not ideal - is there no way you can leave it hooked up for a week or so?

HopIt

Re: Carbonating half full kegs

Post by HopIt » Fri Jan 12, 2018 2:21 pm

I could leave one at a time hooked up for a week. I think will only have space in my kegerator for one keg at a time, so won't be able to carb both at the same time, unless I did so outside of the fridge.

Basically my brew length is about 25 litres, and cornies only hold 19l and have had enough of bottling for a lifetime so am trying work out the best solution. It doesn't help that the 2nd fridge I just got will probably only fit 1 keg in.

Also am a bit concerned about the amount of co2 I'll get through with 2 half full kegs.

Any ideas?

Jambo
Hollow Legs
Posts: 375
Joined: Wed Jul 30, 2008 2:00 pm
Location: Aberdeenshire

Re: Carbonating half full kegs

Post by Jambo » Fri Jan 12, 2018 2:51 pm

Ah OK. Couple of ideas - do you know you can get mini corny kegs, I think about 5L? That would be a nicer solution and only theoretically leave you with a spare litre. No headspace and you could potentially fit both in the fridge?

You could carbonate outside the fridge but you'd need to consider carbing temperature vs serving temperature... Or one in and one out and you could carb at a 'correct' pressure and top up quickly every evening for a week or so.

f00b4r
Lost in an Alcoholic Haze
Posts: 636
Joined: Fri Jul 11, 2014 10:54 pm
Location: Berlin

Re: Carbonating half full kegs

Post by f00b4r » Fri Jan 12, 2018 2:54 pm

Apart from reducing your brewlength or using Jambo’s suggestion? You could use a carbonation cap or three along with a few sparkling water bottles (1.5 or 2L) to fill the rest directly into these, carb with CO2 directly in the bottles and then use the carb cap to just top up with CO2 if you don’t drink all of a bottle quickly. Do a search for on the forum for “ghetto keg overflow” for more details.

Fil
Telling imaginary friend stories
Posts: 5215
Joined: Sun Oct 16, 2011 1:49 pm
Location: Cowley, Oxford

Re: Carbonating half full kegs

Post by Fil » Fri Jan 12, 2018 3:10 pm

You will use more co2, google will help with the formula to calculate mass of co2 in X litres @ Y psi, to give you an idea. but co2 inst expensive if bought in 6-7kg packages, so will imho add pennies not £s to the price of each pint poured.. an off the top of my head guestimate is it may mean buying a co2 refil after 9 months rather than 12+??

but on the flip side if you dont usually keep beer on gas at pressure when conditioning your carbonation will go a lot quicker/ easier with a significantly larger volume of co2 under pressure in each keg, so the chances of depleting the supply if off gas will be much lower..
ist update for months n months..
Fermnting: not a lot..
Conditioning: nowt
Maturing: Challenger smash, and a kit lager
Drinking: dry one minikeg left in the store
Coming Soon Lots planned for the near future nowt for the immediate :(

Fil
Telling imaginary friend stories
Posts: 5215
Joined: Sun Oct 16, 2011 1:49 pm
Location: Cowley, Oxford

Re: Carbonating half full kegs

Post by Fil » Fri Jan 12, 2018 3:15 pm

hows this for an off the wall idea?? If excessive co2 use is a major issue.. make up the 'missing' volume with some inert mass?? like the toilet hippos (bricks) placed in toilet reservoirs to reduce water usage. something you can easily boil sanitise perhaps??

i ebayed a set of SS balls a while back with the intention of using them to weigh down hop bags, i was gutted when they arrived and proved to be hollow shells that floated, but in this case ;)
ist update for months n months..
Fermnting: not a lot..
Conditioning: nowt
Maturing: Challenger smash, and a kit lager
Drinking: dry one minikeg left in the store
Coming Soon Lots planned for the near future nowt for the immediate :(

User avatar
Dads_Ale
Piss Artist
Posts: 172
Joined: Fri Feb 14, 2014 5:58 pm
Location: Newbury UK

Re: Carbonating half full kegs

Post by Dads_Ale » Fri Jan 12, 2018 4:26 pm

I do not reckon there will be any difference in gas usage irrespective of how much beer you put in the corny. It will only take a certain amount of CO2 to reach the required level in the beer.

If you are turning off the cylinder rather than leaving it open 24/7 then with a bigger head space you may well have to use a lower psi value or shorter carbonation time. (bigger head space means more square inches)

Jambo
Hollow Legs
Posts: 375
Joined: Wed Jul 30, 2008 2:00 pm
Location: Aberdeenshire

Re: Carbonating half full kegs

Post by Jambo » Fri Jan 12, 2018 5:20 pm

Dads_Ale wrote:
Fri Jan 12, 2018 4:26 pm
I do not reckon there will be any difference in gas usage irrespective of how much beer you put in the corny. It will only take a certain amount of CO2 to reach the required level in the beer.
Indeed the gas used PER KEG won't change (may actually be less since you're not dissolving it in as much beer and then drinking it), but two kegs i.e. 38 L of keg space for 25L of beer is not an optimal use of gas.

But as Fil points out, the CO2 itself is not particularly expensive, so not worth worrying about.

jaroporter
Drunk as a Skunk
Posts: 983
Joined: Sat Jul 21, 2012 11:12 pm
Location: Garden of England

Re: Carbonating half full kegs

Post by jaroporter » Fri Jan 12, 2018 8:05 pm

i reckon jambo's point about purging the o2 is probably the important one. i either prime kegs or transfer when the yeast is still active as that is supposed to help too. it also saves me using co2 from the tank..

if you're bored of bottling i wouldn't do this though. wait to see how annoying it is when kegs run out quickly and you spend all your time washing something out that doesn't fit in the sink!
maybe just me.. :D

the carbonation caps are always a good shout for overspill, as is minikegs / growlers / just making sure you're kegging when you fancy a beer or two..
dazzled, doused in gin..

Matt in Birdham
Drunk as a Skunk
Posts: 759
Joined: Thu Oct 08, 2015 10:27 pm

Re: Carbonating half full kegs

Post by Matt in Birdham » Fri Jan 12, 2018 8:29 pm

Agree about the O2 - it is very hard to effectively purge a keg of O2 using CO2. Someone ran the numbers once, and although I won't search for them now suffice to say that you would need to burp at least half a dozen times from decent pressure to make a meaningful dent in the O2.
I'm a big advocate of carbonation caps as well, and usually have a few bottles too much for a keg. I fill 500ml pet bottles, cap fridge them "as is" and carbonate them on demand with a carbonation cap at 40 psi and about 4 minutes of shaking. I think of it as something of a treat actually as you can get a pretty good idea of what the beer will be like, so I'm actually disappointed if I don't have least a few bottles worth left over after kegging.

Fil
Telling imaginary friend stories
Posts: 5215
Joined: Sun Oct 16, 2011 1:49 pm
Location: Cowley, Oxford

Re: Carbonating half full kegs

Post by Fil » Fri Jan 12, 2018 8:57 pm

thinking about it no extra co2 will be used in serving.
But when conditioning with excess pressure ie @ 20 or 30 psi, the extra 10l of headroom will have an impact.
If conditioned at serving pressure as the kegging chart enthusiasts would suggest, then again it may not use any extra co2 and in fact use less.. (per keg, tho it will increase nominally the volume of gas used to serve per pint, upto 2x perhaps..)

however the sq inches of beer surface able to absorb co2 wont increase with headspace only the cubic inches of gas sat above, the difference being that pressure will not diminish as rapidly with absoption if off gas as it would with only a nominal headspace as found in a full keg...
ist update for months n months..
Fermnting: not a lot..
Conditioning: nowt
Maturing: Challenger smash, and a kit lager
Drinking: dry one minikeg left in the store
Coming Soon Lots planned for the near future nowt for the immediate :(

AdrianTrace
Piss Artist
Posts: 139
Joined: Tue Feb 23, 2010 12:42 am
Location: Botley, Hampshire

Re: Carbonating half full kegs

Post by AdrianTrace » Sat Jan 13, 2018 7:47 pm

I don't think it matters that much - I don't leave the gas hooked up when carbonating, either. I do either 14l or 19l brewlengths, so the keg headspace varies accordingly.

After purging I whack it up to 50-60psi and disconnect. For the 14l brewlength this drops to 14-20psi over the next few days, which is where I tend to keep them, depending on season (bit lower in winter). The 19l brewlength drops down to minimal 2-3psi, so I have to keep bumping it back up over the next few days as it dissolves until it reaches the right point.

I figure that at that point there is the same CO2 used as when 5l of the 19l keg has been consumed and replaced by gas. :-k Possibly less, as the consumed beer would have CO2 dissolved in it... but the purging would take more CO2 :-k

See! not worth worrying about - probably bugger all difference :D and far less than when you get a leak :evil:
Ready to go: Malt extract, grain, yeast and a freezer full of hops.
Fermenting: Nowt.
Conditioning: Nelson's Revenge.
Drinking: Stop Wining, Firsty Gold, DarkMun, Yankee, Porter, ApAht, Cider, Mead, Tripel, Elderflower beer, Gluten Free, beer, wine, port, gin,beer, wine, port, gin...

Post Reply