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The old keg foams as the beer disappears trick

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Georgedgerton

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While I have been home brewing since the early days (50 years ago for Pete's sake) most of that was bottled conditioned and I only really got in to kegging a couple of years back. Since then I have had all the issues of a newbie getting the set up right but suffered the old beer goes great for 2/3 the keg and gradually starts to poor more and more foam as it gets to the end. Went though the line length and dia stuff, serving pressure (which I carbonate at) right through to crap in the line and measuring the temperature for the top of the keg to bottom, all with no real explanation or real way to fix. Then found out as the volume of the beer drops, it absorbs the carbonation very rapidly, even though the pressure is stable. Even worse as it pours foam and the head collapses back in it looses the carbonation. So all you expert Keggers, I'm sure you have experienced this and overcome it. Regardless as old as topic as it is, I could do with some help from those in the know
 

Dozer71

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Have you checked the dip tube to ensure it doesn't have a hole in it about 2/3 the way down. I did hear of some having this problem.
 

MHB

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Going to try and keep this short and simple, got something to do soon so not being terse, just in a bit of a rush.

1/ The amount of CO2 in solution is directly related to the temperature and the pressure, here is the equation (Braukaiser Carbonation Tables)
2/ At a given temperature the amount of CO2 in solution will in time form an Equilibrium (this is important). At equilibrium the same amount of CO2 is going into the beer as is coming out of the beer, they are Equal, so there is no net change. Remember that it takes time to reach an equilibrium. Change the temperature and/or the pressure and the equilibrium point will change.
3/ CO2 enters the beer through the surface, a full or nearly empty keg as the same interface area between the liquid and the gas above it. The Volume to be conditioned and the area through which gas can defuse is known Aera:Volume (A:V) in science its M^2 : M^3 (Square meters to Cubic meters). More area to volume the system will move to equilibrium faster, and the converse applies. Shaking or using an airstone increases the area accelerating the movement of gas into/out of solution.

Those are the three main parameters. Alter any of them and the amount of CO2 in solution will change.
To keep the temperature fixed, make sure the thermostat on the fridge is reasonably accurate (holds to within 1-2oC). Fit a fan inside the fridge, this stops the formation of thermal layers which can easily be 5oC over the height of a fridge. Hasn't got to be very big a small computer fan is heaps.

Keeping the temperature homogeneous means you avoid the change in temperature that occurs as the beer level in the keg falls. If the fridge is colder at the bottom the beer in a less full keg will be colder than the top you will get increased CO2 in Solution.
The other really important factor is that as the level in the keg falls the gas interface aera changing the A:V so the changes in dissolved CO2 happens faster as the keg gets both Colder and as the A:V increases
Put in simplest terms, at a constant pressure -
Les colder beer, gas goes in faster
You are moving to a new higher equilibrium and further away from you target control point.
Put a little fan in the fridge.
Mark
 

Georgedgerton

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Have you checked the dip tube to ensure it doesn't have a hole in it about 2/3 the way down. I did hear of some having this problem.
Sure have , changed O rings all that stuff, so frustrating
 

Georgedgerton

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Going to try and keep this short and simple, got something to do soon so not being terse, just in a bit of a rush.

1/ The amount of CO2 in solution is directly related to the temperature and the pressure, here is the equation (Braukaiser Carbonation Tables)
2/ At a given temperature the amount of CO2 in solution will in time form an Equilibrium (this is important). At equilibrium the same amount of CO2 is going into the beer as is coming out of the beer, they are Equal, so there is no net change. Remember that it takes time to reach an equilibrium. Change the temperature and/or the pressure and the equilibrium point will change.
3/ CO2 enters the beer through the surface, a full or nearly empty keg as the same interface area between the liquid and the gas above it. The Volume to be conditioned and the area through which gas can defuse is known Aera:Volume (A:V) in science its M^2 : M^3 (Squair meters to Cubic meters). More area to volume the system will move to equilibrium faster, and the converse applies. Shaking or using an airstone increases the area accelerating the movement of gas into/out of solution.

Those are the three main parameters. Alter any of them and the amount of CO2 in solution will change.
To keep the temperature fixed, make sure the thermostat on the fridge is reasonably accurate (holds to within 1-2oC). Fit a fan inside the fridge, this stops the formation of thermal layers which can easily be 5oC over the height of a fridge. Hasn't got to be very big a small computer fan is heaps.

Keeping the temperature homogeneous means you avoid the change in temperature that occurs as the beer level in the keg falls. If the fridge is colder at the bottom the beer in a less full keg will be colder than the top you will get increased CO2 in Solution.
The other really important factor is that as the level in the keg falls the gas interface aera changing the A:V so the changes in dissolved CO2 happens faster as the keg gets both Colder and as the A:V increases
Put in simplest terms, at a constant pressure -
Les colder beer, gas goes in faster
You are moving to a new higher equilibrium and further away from you target control point.
Put a little fan in the fridge.
Mark
wouldn'
Going to try and keep this short and simple, got something to do soon so not being terse, just in a bit of a rush.

1/ The amount of CO2 in solution is directly related to the temperature and the pressure, here is the equation (Braukaiser Carbonation Tables)
2/ At a given temperature the amount of CO2 in solution will in time form an Equilibrium (this is important). At equilibrium the same amount of CO2 is going into the beer as is coming out of the beer, they are Equal, so there is no net change. Remember that it takes time to reach an equilibrium. Change the temperature and/or the pressure and the equilibrium point will change.
3/ CO2 enters the beer through the surface, a full or nearly empty keg as the same interface area between the liquid and the gas above it. The Volume to be conditioned and the area through which gas can defuse is known Aera:Volume (A:V) in science its M^2 : M^3 (Squair meters to Cubic meters). More area to volume the system will move to equilibrium faster, and the converse applies. Shaking or using an airstone increases the area accelerating the movement of gas into/out of solution.

Those are the three main parameters. Alter any of them and the amount of CO2 in solution will change.
To keep the temperature fixed, make sure the thermostat on the fridge is reasonably accurate (holds to within 1-2oC). Fit a fan inside the fridge, this stops the formation of thermal layers which can easily be 5oC over the height of a fridge. Hasn't got to be very big a small computer fan is heaps.

Keeping the temperature homogeneous means you avoid the change in temperature that occurs as the beer level in the keg falls. If the fridge is colder at the bottom the beer in a less full keg will be colder than the top you will get increased CO2 in Solution.
The other really important factor is that as the level in the keg falls the gas interface aera changing the A:V so the changes in dissolved CO2 happens faster as the keg gets both Colder and as the A:V increases
Put in simplest terms, at a constant pressure -
Les colder beer, gas goes in faster
You are moving to a new higher equilibrium and further away from you target control point.
Put a little fan in the fridge.
Mark
I am aware of that, but wouldnt have thought less than a 2 dg temp range from top to bottom would have caused such a differnence
 

MHB

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If you don't like that answer, maybe conjuring with the right magic words will fix the problem for you, you could try prayer, sacrificing to your favorite god... or stick with science

Don't forget that its not just 2 dg difference, there is time to include to. As you get closer to the bottom if you are emptying the keg fairly quickly you are into double whammy, its getting colder and the A:V is increasing so the speed the CO2 is going into the beer is accelerating.
Not knowing how long the beer has been sitting under pressure I cant tell if it ever reached equilibrium, if you aren't patient it possibility hasn't, so odds on your at a bit higher pressure than you could be for best results.
Worth taking a look at the carbonation tables to see just where your settings are at.
Mark
 

Georgedgerton

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Taking onboard what you're saying and it's not that I didn't like your answer, I was just a bit surprised a couple dg would make such a difference, but as you have pointed out, there is more to it than just that, and I do appreciate you taking the time to reply
 

kadmium

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Taking onboard what you're saying and it's not that I didn't like your answer, I was just a bit surprised a couple dg would make such a difference, but as you have pointed out, there is more to it than just that, and I do appreciate you taking the time to reply
Do you have a gas manifold or check valves?
 

Kodos

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As I'm sure you learned getting this far, getting the system balanced can take a bit of trial and error (more error on my part). And it's even harder if you don't have flow-control taps.

Part of balancing the system is factoring in the height difference between the beer and the keg (rise). Generally you take the measurement from the middle of the keg, and figure that a little above, or a little below that as the beer volume in the keg changes is OK.

But maybe your system notices this affect more (depending on the current rise in your system)? So as the beer has to be pushed that extra 30cm higher, the extra resistance is causing foaming in the lines? (as opposed to over-carbing).

I'm having trouble quickly finding a decent metric calculator, but playing around with this Beer Line Length Calculator suggests that a height difference of 1 foot could require a difference of 0.78 foot of beer line (23cm), which isn't insignificant when trying to get your beer line length perfect. Maybe as the keg empties you'll want to tweak the serving pressure to account for this? It may seem counter-intuitive, but you might want to bump up the pressure a smidge to counter the extra resistance from gravity pushing the beer up higher?

Might be worth a try at least.
 

kadmium

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As I'm sure you learned getting this far, getting the system balanced can take a bit of trial and error (more error on my part). And it's even harder if you don't have flow-control taps.

Part of balancing the system is factoring in the height difference between the beer and the keg (rise). Generally you take the measurement from the middle of the keg, and figure that a little above, or a little below that as the beer volume in the keg changes is OK.

But maybe your system notices this affect more (depending on the current rise in your system)? So as the beer has to be pushed that extra 30cm higher, the extra resistance is causing foaming in the lines? (as opposed to over-carbing).

I'm having trouble quickly finding a decent metric calculator, but playing around with this Beer Line Length Calculator suggests that a height difference of 1 foot could require a difference of 0.78 foot of beer line (23cm), which isn't insignificant when trying to get your beer line length perfect. Maybe as the keg empties you'll want to tweak the serving pressure to account for this? It may seem counter-intuitive, but you might want to bump up the pressure a smidge to counter the extra resistance from gravity pushing the beer up higher?

Might be worth a try at least.
I find flow control taps worse for foaming as I believe the flow control should be done by a properly balanced system rather than the mechanism on the tap. That's my opinion though.


I don't think rising is an issue, especially if OP is using 4mm beer line. I think increasing pressure will cause more issues.

I would think that the beer is over carbing over time, and that it just needs to balance out properly.

You need about 1.5m of 4mm beer line to provide enough resistance to reduce foaming. Too short it will flow too fast, too long and it will flow too slowly causing foaming. Then you bump the pressure to get it to pour faster and it seems OK and then a week later its over carbed and pouring foam.

The correct way is to use forward sealing taps, with properly balanced lines to ensure adequate flow rate to the desired vol you want. It makes it hard to have multiple pressures IE heffeweizen on one and stout on the other. It can be done but you would need inline regs and appropriate beer line lengths for each style.

In short, the higher the pressure the longer the line you will need. So you will need to either bump the line length up or lower the pressure. I have found that with my line length, I run about 11PSI and that gets me a nicely carbed beer at 4 degrees.

Also, check valves can inhibit pressure so bear that in mind. So for instance one check valve may reduce by 1PSI and another may reduce by 2PSI so one keg may be higher by 1PSI (10%) simply via the check valves. Have you found one beer tap does it more than the others?
 

MHB

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Taking onboard what you're saying and it's not that I didn't like your answer, I was just a bit surprised a couple dg would make such a difference, but as you have pointed out, there is more to it than just that, and I do appreciate you taking the time to reply
If you look at the equation its pretty clear why temp plays such a big role
Condition in g/L = Absolute Pressure (Gauge + Atmospheric) X Solubility Constant to the power of (^) Constant/Temperature (in k or absolute).

Kodos
The pressure involved in lifting the beer will have a much larger effect on the flowrate, adjusting the pressure will make it very difficult to control condition.
Personally I would set the system to give the perfect carbonation for the beer I'm drinking as above multiple regs would make life easy. Then adjust the lines to give a reasonable flow.
If you assume the keg is about 600mm high and had a FG of 1.010 the dynamic difference over the keg would be, from P=Ro*g*h =1.010*9.81*.6 = 5.9kPa (0.86 PSI for the luddites)

Considering how little they cost I'm thinking of going to beer pumps, get the beer dialed in and set the flow all easy peasy.
Mark
 

Georgedgerton

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Look thanks for all your help, no doubt I can sort it, and while I have tried to get most aspects right, things obviously still need tweaking. Interesting kadmium said he found flow control taps worse for foaming rather than getting the system right. I have flow control taps and sometimes this problem seems worse than at other times; so now wondering if the taps (especialy if you have been mucking around with them) may not be at least a factor in my problem
 

kadmium

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Look thanks for all your help, no doubt I can sort it, and while I have tried to get most aspects right, things obviously still need tweaking. Interesting kadmium said he found flow control taps worse for foaming rather than getting the system right. I have flow control taps and sometimes this problem seems worse than at other times; so now wondering if the taps (especialy if you have been mucking around with them) may not be at least a factor in my problem
I just feel the mechanism can add turbulence and are finicky with cleaning. A piece of debris stuck in there etc can knock co2 out of solution.

That's my opinion. I'm not saying they are bad, they have definite uses. I just think they aren't a silver bullet for a non balanced system.
 

Georgedgerton

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I certainly think there is merit in what you say, I previously had an issue where the keg just suddenly started foaming in the early stages, suspected just that, took the tap apart, cleaned it out and the problem went away when I put it back.
 

onemorecell

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I find flow control taps worse for foaming as I believe the flow control should be done by a properly balanced system rather than the mechanism on the tap. That's my opinion though.
Last week I swapped one of my FC taps over to a regular forward sealing one for a test run, and it pours SO much better. I'll probably update all of mine to this.

I always get this same problem. No idea how to fix it...
- have a fan running
- fridge varies between 2-4 degrees, with thermometer in a wine bottle of sanitiser to stay more static
- beer lines are fine (probably?)
- i use a 4 way manifold
 

kadmium

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Last week I swapped one of my FC taps over to a regular forward sealing one for a test run, and it pours SO much better. I'll probably update all of mine to this.

I always get this same problem. No idea how to fix it...
- have a fan running
- fridge varies between 2-4 degrees, with thermometer in a wine bottle of sanitiser to stay more static
- beer lines are fine (probably?)
- i use a 4 way manifold
Try dropping the pressure by 1 PSI and seeing if that helps, but it should have a fair bit of play in it.

Yeah I like simple forward sealing taps personally. I think FC were introduced before you could get the small EVA lines we get now, as they used to be bigger beverage lines and people in the states especially always seem to have miles of big line.
 

MHB

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The quality of taps, line and fittings makes a big difference to how well your beer will pour.
The difference between one of the pro Brumby from Andale or Lancer (something Japanese) alongside one of the cheap knockoffs has to be seen to be believed.
Low quality systems can be impossible to control properly and will always foam. That said it isn't the problem the OP is having, that is down to dissolved CO2 levels changing.

I'm inclined to agree on Flow Controllers causing more trouble than they are worth. Don't agree on forward/back seal issue. The old EK, Flowrite and DA taps are all forward sealing, Brumby (the best selling commercial tap in Australia) is back sealing. All of them will pour well on a well designed and set system.

Onemorecell I would be looking to get better temperature control than you have. It can be a disadvantage to have the sensor in water, if the temperature of the water is moving up and down in a 2oC band the air temperature is probably moving a lot more. Worth trying it just stuck to the side of the fridge (especially if you have a fan) and have a look at your band width adjustment, narrow that down to 1oC max.

As mentioned before, its really important to first establish how much dissolved CO2 you want in your beer.
Then create the conditions you need to get that level of carbonation - look at the carbonation tables - if you are drinking mostly say APA and serve it at say 4oC, and want 5g/L of dissolved CO2, you need 80kPa to get and maintain that amount of fizz.
Then design/build a system that will pour well at those conditions.

One point worth noting.
Gauges on most regulators are far from precision instruments, seen plenty out by 10% and more than a few out by 20%. It would be nice if we could all afford certified pressure gauges but I sure cant. If you set the reg to give a reported say 80kPa and you aren't getting the fizz you want there is a decent chance the reading is off. If you have a couple of regs testing them against each other and seeing if there is a big difference isn't a bad notion. I used to be able to drop in to the Mech Engineering school at my local TAFE and get one of the guys to test gauges for me. One place I knew had a very good digital gauge in the keg conditioning circuit plugging in to that was pretty handy. One retirement and a business closing and I'm back to guessing. Have to come up with an alternative.
Mark
 

BKBrews

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I just feel the mechanism can add turbulence and are finicky with cleaning. A piece of debris stuck in there etc can knock co2 out of solution.

That's my opinion. I'm not saying they are bad, they have definite uses. I just think they aren't a silver bullet for a non balanced system.
I definitely agree with this. I started out with flow control perlicks, and when I bought a bigger freezer to increase capacity, I opted to add cheap ultrataps for the additional, with no flow control. Using PSI charts and beer line calculators, I worked out the correct line length for all of my taps (worked out to just over 4m of 5mm ID line on all taps). The flow control taps still feel a little bit unbalanced, and even with the flow control fully open, they do not pour as well as the much, much cheaper ultrataps. That said, I still prefer them - they are a waaaaaay better build!
 

onemorecell

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Onemorecell I would be looking to get better temperature control than you have. It can be a disadvantage to have the sensor in water, if the temperature of the water is moving up and down in a 2oC band the air temperature is probably moving a lot more. Worth trying it just stuck to the side of the fridge (especially if you have a fan) and have a look at your band width adjustment, narrow that down to 1oC max.
A good point - but the intention is also to prevent the compressor turning on and off so often. I'm using a chest freezer and apparently this is better for them.
Bit of a catch 22...

The temp adjustment is at 1 degree. I've got it set to 3 and it fluctuates between 2-4
 
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