One of the joys of kegging your beer is not having to endlessly clean bottles or them occasionally exploding in your garage. Force carbonating is also another advantage of kegging, allowing you to carbonate faster and without the sediment found in the bottom of the bottle when naturally carbonating.
Of course you can naturally carbonate in a keg by adding the correct amount of sugars and keeping it warm for about two weeks but most people prefer to 'force' the carbonation into the beer using a CO2 cylinder. Contrary to some people's beliefs, force carbonating does not affect the head retention or size of the bubbles in the beer, CO2, once dissolved into the beer is the same weather it comes from a cylinder or produced by the yeast.
Although the principal is the same, there are many different techniques to carbonate in a keg. There are three 4 main factors at play when force carbonating, pressure, temperature, surface area and time.
Pressure and temperature are both related and determine the carbonation level of the beer. Typical beers will have a carbonation level around 2.4 - 2.6 volumes of CO2 by less common styles can have much higher or lower carbonation. The higher the temperature of your beer the higher the pressure will need to be inside the keg to achieve the desired carbonation level. The table below shows the pressure required to achieve your desired carbonation depending on the temperature.
Obviously the whole keg won't be carbonated as soon as you set this pressure on your regulator. Over time the beer will approach the carbonation level determined by the pressure and temperature depending on the surface area to volume of the keg. Shaking the keg or using a carbonation stone effectively increases the surface area hence reduces the time.
With this information in mind we'll explain three techniques to carbonate in your keg.
Set & Forget Method
This is the simplest and safest way to carbonate the beer in your keg. Although it takes more time to achieve than force carbonating rapidly, there is no risk of over carbonation. It is much easier to get CO2 into beer than it is to get it out!
This method simply requires you to set the pressure on your regulator using the chart above. Typically this consists of chilling your beer down to the desired serving temperature, commonly 2oC and setting your regulator at around 9-11psi which will carbonate a beer around the 2.4 to 2.5 CO2 volume mark over the course of 5-8 days.
Semi-Speed Carbonation Method
If you're in more of a hurry to carbonate you can speed up the process after you’ve cold crashed your beer, setting your pressure to 30psi for 2 days. Then revert back to equilibrium pressure and waiting another couple of days to get that last bit of carbonation. It has some risk involved in over carbonation, as if you forget the beer at 30 psi it will eventually reach about 4.5 volumes of CO2 but it will reduce the time required by a couple of days.
Rapid Force Carbonation Method
We’ve all been there, a brew smells amazing as it comes out and you just want a cold drop of it immediately and of course ‘fizzy’. What’s a frothy without the froth!!
This method consists of applying high levels of CO2 at approximately 30-50psi and roll, shake, dip dive and dodge their kegs for 1-3 minutes depending on how cold the beer is and what pressure you set it to. This shaking/rolling action helps the liquid absorb the CO2 much quicker by increasing the surface area. As you're shaking the keg you'll hear gas hiss through the regulator and bubble through the beer. There are many variables such as the exact pressure, temperature, flow rate of gas through your regulator and check valves ect, how vigorously you shake the keg and how full the keg is which will determine exactly how long this will take. It can take a but of trial and error to find what works for you and your system.
As a good starting point turn your regulator to 35 psi and shake vigorously for 45 seconds. Give the beer 10-15 minutes to settle before pouring a small glass to taste the carbonation level. If it's a bit low, raise to 35 psi and shake again for 15 seconds, wait and taste again. If you choose to use this method it is important to keep all the factors above consistent from keg to keg to get consistent carbonation levels, take notes so you'll remember for the next keg. This method is highly HIGHLY prone to over carbonation if you are new to the homebrewing game. Done correctly this is the quickest method to carbonate your brew, if you get to zealous though you'll have to wait as much time as the set and forget method or more to decarbonate the keg.
There are some other variables affecting how much it CO2 will saturate into the solution such as remaining sugar levels in the finished beer, and the alcohol content but these tend to be insignificant for most homebrewers.
Carbonation Keg Lid
If shaking your keg isn't really your style another option for speeding up your carbonation time is the carbonation keg lid. This is a cornelius style keg lid with a ball lock post on the lid with a 0.5 micron carbonation stone attached. This greatly increases the surface area of the CO2 by bubbling tiny bubbles through the beer. Full instructions on how to use the carbonation keg like can be found here.