Carbonation Question

R

Robert McKeon

Member
I brewed a batch of honey Kolsch and Keg carbonated to 2.5 vol co2.
Put into kegerator at 50 degrees and let carbonate for 2 weeks at 13 psi.
Lowered the CO2 Pressure to 10 psi to serve at 40 degrees.
Left at that for 2 weeks but thought was a little under carbonated.
Turned pressure up to 15psi and let sit for another week.
Beer was all foam and way over carbonated.
My question is:
I thought once it was carbonated it was done and couldn't be changed. Is appears that is not the case.
Can you always take an under carbonated beer and jack up the carbonation level at anytime?

Any thoughts?
Thanks, Bob
 
Yes, you can add co2 to a keg at any time and add additional carbonation. The opposite is also *sort* of true, if you can get the co2 out of solution (shake, purge, shake, purge, etc) you can lower carbonation on a beer by putting it under no, or less pressure.

40 degrees at 15psi (assuming your temps are correct, your regulator is working, etc) should give you about 2.7 vol of c02 (http://www.kegerators.com/carbonation-table.php), which should be fine for a Kolsch. If it's all foam it might not overcarbed, but your kegerator might not be balanced.

What type of faucet? How long is your beer line? Is the beer line cold the whole way? Tower, or shanks through a fridge wall (how high does the beer have to travel to get to the faucet from the keg?) What could be happening is that the beer itself is carbed correctly, but your keg system is letting too much of the carbonation out while it's pouring, causing foam.

I carb my beers at room temperature, 68-72 degrees, at about 28 psi for a week or two. Usually gives me a good carb range. Might not be exact, but it's close enough. Then add to the fridge, let it cool overnight, and serve the next day. I serve between 8 and 10 PSI with 9ft of line.
 
Thanks
I have a small igloo keg setup.
The temp is right because I keep a thermometer on top of keg to verify.
The lines are very short.
Probably only about 4' of line to tap.
Think I should be using longer lines?
Standard 1 tap tower made for the igloo setup.
Faucet is chrome plated brass.
Just kicked the keg last night and this is the first time it has happened in about 4 kegs I've done.
I have an industrial quality regulator (about 250 bucks) so I think that is ok.
Just trying to get smarter for next time to avoid in future.
 
Someone else here probably knows the math behind the balancing of the draft lines, but 4' is way short. At that length your serving pressure should probably only be 5 or 6 psi I would guess. If you served through 4' of line at 15 psi, you're going to get nothing but foam if you have carbonation in your liquid at all.

What you shoul do is carb to your desired volumes of C02 based on a carb chart like I posted above, then turn down the pressure to serve pressure so that it doesn't foam like crazy when pouring.

I also have no idea what an "igloo keg setup" looks like, care to share a picture?
 
Ah didn't realize igloo made fridges as well as coolers. I thought you had built some sort of cooler/kegerator thing out of a cooler or something.

So, yeah, lines still short (which is fine, but you'll need to have a lower pressure) and don't dispense at 15 with those size lines and see if that helps.
 
If you find your beers not fully carbed with a low regulator psi (under 10) you may want to increase your beer line lengrh. I have 10ft lines and my regulator is at 14psi. Balancing the system may take some time and trial and error, but totally beats bottling.
 
An article I saved from BeerSmith email:
Line Resistance is Not Futile

So how does one design a draft beer system to maintain proper balance at the tap? The pressure drop depends on resistance in the beer line. Beer lines have two types of resistance - one due to elevation change (i.e. the keg being higher or lower than the tap), and a second due to the beer lines themselves which generate friction as the beer flows through the lines.

Lets look at resistance first to keep things simple. Here are some sample resistance ratings for various popular beer lines:

3/16" ID vinyl tubing = 3 psi/ft
1/4" ID vinyl tubing = 0.85 psi/ft
3/16" ID Polyethylene tubing = 2.2 psi/ft
1/4" ID Polyethylene tubing = 0.5 psi/ft
3/8" OD Stainless tubing = 0.2 psi/ft
5/16" OD Stainless tubing = 0.5 psi/ft
1/4" OD Stainless tubing = 2 psi/ft
Generally plastic tube of smaller than 3/16" ID is not recommended - it provides too much resistance for practical use!

So now that we have the resistance factors how to we go about designing a keg system that is in balance? For the purpose of our example lets assume that you have pressurized your kegging system at a nominal 12 psi, which at a 40F refrigerator temperature represents a mid range carbonation level of about 2.5 volumes of CO2 - typical for an average American or European beer.

At the tap end of our balanced keg system we want a slight positive pressure to push the beer out, but not enough to foam. Generally this would be between less than 1 psi. So let's target a tap end pressure of 1 psi. The math from here is pretty easy to calculate the balanced line length (L):

L = (keg_pressure - 1 psi) / Resistance
So starting with our example of 12 psi keg pressure, and some typical 3/16" vinyl keg tubing (which loses 3 lb/ft) we get L= (12-1)/3 which is 3.66 feet. So a 12 psi kegging system would provide 1 psi of pressure at the tap with 3.66 feet of tubing.

Note that some authors leave out the 1 psi tap pressure (i.e. use zero tap pressure) and simplify the equation to L= (keg_pressure/Resistance) which makes the math even easier (the simplified equation would give you 4 feet of tubing vs 3.66 ft). The truth is that you can target anywhere between zero and 1 psi at the tap and still be in balance - the difference is relatively small, though a slight positive keg pressure will give you a better flow rate.

The four foot example with 3/16" ID vinyl is great if we only have a few feet to go (i.e. in a fridge) but what if one needs to go further? A simple switch to 1/4" ID vinyl tubing will get us there - looking at the same 12 psi keg system we get: L = (12-1)/0.85 = 12.9 feet. So with the larger tubing we can deliver our beer to just under 13 feet. For other applications we can consider polyethylene or stainless. However if going a long distance one needs to also consider refrigeration - as you don't want a large volume of warm beer in the lines.

Beer Line Length and Elevation

Changes in elevation also come into play if you design a more complex serving system. The rule of thumb is that your beer loses 0.5 psi/foot of elevation gain. So if your tap is 1 foot higher than the keg it loses 0.5 psi, and conversely if it is lower than the keg it will gain 0.5 psi per foot of elevation.

So if we roll this into our equation, we get the following for a given height (Height - in feet) of the tap above the keg itself:

L = (keg_pressure - 1 - (Height/2)) / Resistance
So lets go back to our original example of a 12 psi keg pressure, 3/16" ID vinyl tubing and this time put the tap 2 feet above the keg itself. We get L=(12-1-(2/2))/3 which is 10/3 or a line length of 3.33 feet.

Another example with longer lines: 12 psi keg pressure, 1/4" ID vinyl and a tap four feet above the keg gives: L=(12-1-(4/2)/0.85 which is 9/0.85 or 10.6 feet of line length.


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The only way to have different CO2 pressures is with a separate regulator or split regulator. So if you wanted to serve both British ales and Belgians at their appropriate CO2 levels, you would need a dual regulator or 2 separate tank/regulator sets.
 
Yes, if you have a single regulator then all beers on tap have to be at the same carbonation / dispensing pressure. You can theoretically carbonate one keg at a higher or lower level than the rest (and use a longer or shorter line to serve), but once it's on tap it will eventually gain or lose carbonation to match the system. The only real way to have beers at multiple CO2 levels is to use multiple regulators.

To much bother for me; I target a slightly-higher-than-average carbonation level and just use that for everything. My English beers are a little overcarbed (not too much, but certainly not "cask style" either), and my spritzier beers are a little under.

Here's the draft line length calculator I've been using:
http://www.mikesoltys.com/2012/09/17/de ... kegerator/

Also, for anyone using the EJ Bev barrier tubing (https://www.brewhardware.com/product_p/ ... 316bev.htm), note that it is sold as 3/16" (0.1875") but it's really 1/5" (0.2"). Plan accordingly, I did not and now I have to redo the whole thing. :evil:
 
I have a dual regulator and can handle 2 pressures: 1 regulator is hooked to 1 gas line for various uses (carbonating kegs, or lower/higher carb level keg) the other regulator is hooked to a 4 way splitter for the other kegs.
It wasn't too expensive to do.


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Coming in on this post late, but am curious what exit pressure will generate foam? I have seen posts on other home brewing blogs that talk about 8-10psi (keg pressure) and others which mention 2-4. Based on Matt's excellent piece on line resistance and length, I assume the authors of these comments are stating the keg pressure that works best in THEIR configuration. The mystery and trial and error can be overcome if there was an ideal pressure at the tap you needed to hit.

What do bars do? Is this also their problem with the occasional foamy drafts when changing kegs?
 
pressure drop across the tap should be minimized. higher pressure drop through the tap results in more velocity - more turbulence in the beer. This higher energy will cause a bigger dip in instantaneous pressure and can go below the pressure needed to keep the CO2 in solution. by the time the pressure recovers the CO2 will have come out of solution...this is why you should always open a tap fully when you pour a beer.


TL;DR - use the information matt gave and try to get the pressure at the tap to as close to 0 as you can.
 
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