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There are many different methods of artificial carbonation,
from the simple 'shaking keg' method, to in-line pin-point carbonators
with high speed pumps. They all share in common, however, a
few simple principles that, when understood will allow you to
achieve perfect levels of carbonation every time. The following
handout is designed to help you understand what carbonation
is, how it is measured, and how to aim for a desired level of
carbonation in your beer.
What is Carbonation?
Carbonation is the process of injecting or dissolving carbon
dioxide gas in a liquid to create an effervescence of pleasant
taste and texture. In order to force-carbonate a liquid, two
conditions have to be met: The liquid must be cold enough to
accept the gas, and the liquid must be in a sealed pressure
vessel to allow the gas to forced in under pressure.
Why cold?
It has to do with the fact that carbon dioxide is soluble
in a solution in an inverse relationship to the temperature
of the solution. You can visualise this by thinking about
two cans of soda pop. If you keep one can on ice, when you
open it, it will foam very little, and the soda will be strongly
fizzy on your tongue. If you keep the other in the back window
of your car on a summer day, it will foam explosively when
you open it, and after that will seem flat and bland. That
is because the carbon dioxide gas in the warm soda has escaped
from solution. As a general rule of thumb in carbonation procedures,
cold=good.
As for pressure vessels, most of these will
commonly be soda kegs, or beer kegs. There are some other sealed
pressure vessels on the market, but they are proprietary designs
of the manufacturer, and none are as easy to use as the soda/beer
models. Be sure that all of your pressure vessels have proper
safety fittings, and are clean and sanitised before use.
How is Carbonation Measured?
Carbonation is measured in Volumes of CO2. One volume of CO2
is equal to one litre of carbon dioxide dissolved in one litre
of liquid, two volumes is equal to two litres of gas in one
litre of liquid, etc. Remembering this definition isn't important,
but this is the only way measurements of 'fizziness' are defined.
Examples of Carbonation
Levels
Most North American commercial beers are carbonated to 2.5-2.9
volumes. British cask ales are between 1.5 and 1.8 volumes
(this 100% difference in carbonation is the reason why a lot
of North Americans think the British drink their beer 'flat'),
while some German Weizen beers have 3.0-3.5 volumes. While
it is a matter of individual taste, most people will appreciate
a beer that has about 2.4-2.6 volumes of CO2.
The Carbonation Chart
As was stated above, the colder the liquid is, the easier
carbon dioxide will dissolve into it. The following chart
shows the maximum volume of CO2 that a beer will hold at a
given temperature. To use this, look up the volume of CO2
that you wish to dissolve in the beer, cross reference it
to the temperature your beer is at, and this will tell you
the gas pressure needed.
| Deg. F |
Deg. C
Deg. C
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PSI |
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1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
10 |
11 |
12 |
13 |
| 30 |
-1.11 |
1.82 |
1.9 |
2.03 |
2.14 |
2.23 |
2.36 |
2.48 |
2.6 |
2.7 |
2.82 |
2.93 |
3.02 |
- |
| 31 |
-0.56 |
1.78 |
1.9 |
2 |
2.1 |
2.2 |
2.31 |
2.42 |
2.54 |
2.65 |
2.76 |
2.86 |
2.96 |
- |
| 32 |
0.00 |
1.75 |
1.9 |
1.95 |
2.05 |
2.16 |
2.27 |
2.38 |
2.48 |
2.59 |
2.7 |
2.8 |
2.9 |
3.01 |
| >33 |
0.56 |
- |
1.8 |
1.91 |
2.01 |
2.12 |
2.23 |
2.33 |
2.43 |
2.53 |
2.63 |
2.74 |
2.84 |
2.96 |
| 34 |
1.11 |
- |
1.8 |
1.86 |
1.97 |
2.07 |
2.18 |
2.28 |
2.38 |
2.48 |
2.58 |
2.68 |
2.79 |
2.89 |
| 35 |
1.67 |
- |
- |
1.83 |
1.93 |
2.03 |
2.14 |
2.24 |
2.34 |
2.43 |
2.52 |
2.62 |
2.73 |
2.83 |
| 36 |
2.22 |
- |
- |
1.79 |
1.88 |
1.99 |
2.09 |
2.2 |
2.29 |
2.39 |
2.47 |
2.57 |
2.67 |
2.77 |
| 37 |
2.78 |
- |
- |
- |
1.84 |
1.94 |
2.04 |
2.15 |
2.24 |
2.34 |
2.42 |
2.52 |
2.62 |
2.72 |
| 38 |
3.33 |
- |
- |
- |
1.8 |
1.9 |
2 |
2.1 |
2.2 |
2.29 |
2.38 |
2.47 |
2.57 |
2.67 |
| 39 |
3.89 |
- |
- |
- |
- |
1.86 |
1.96 |
2.05 |
2.15 |
2.25 |
2.34 |
2.43 |
2.52 |
2.61 |
| 40 |
4.44 |
- |
- |
- |
- |
1.82 |
1.92 |
2.01 |
2.2 |
2.3 |
2.39 |
2.47 |
2.56 |
2.65 |
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Things to Keep In Mind...
This carbonation chart assumes 100% efficiency of CO2 uptake.
If you have a very large head space in your keg (i.e.; 23
litres of beer in a 50 litre keg) you will probably need to
vigorously carbonate your keg at a higher pressure, and then
reduce the gas pressure to allow it to condition. In addition,
the act of bottling your beer will allow a little CO2 to escape,
so slightly more carbonation will be needed to compensate.
Most commercial quality (Brew-On-Premise) carbonating
systems don't allow for 100% efficiency of uptake: they rely
on 'overkill', putting a high CO2 pressure on the keg and
using the carbonation recirculating pump for a short period
of time to force it into solution. People using these systems
should consult the manufacturers instructions for carbonation
times and pressures. The chart provides the correct data for
carbonating your beer, but there's no substitute for knowing
your equipment's characteristics.
No matter what kind of system you use,
your beer will display better carbonation characteristics
if you allow it to condition. Conditioning is the process
of allowing the bubbles to become finer and finer in solution.
If you carbonate and attempt to dispense immediately, the
bubbles will be large and unstable. Allowing the beer to rest
overnight at carbonating temperature will yield finer bubbles
and longer lasting carbonation.
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