Proper Serving Pressures
(The following information comes directly from
Northern Brewer. They said it best, so I'm not going to try to
re-word this knowledge and pass it off as my own. I will give
credit where credit is due.)
"Brewers express the amount of carbonation in a
beer in 'volumes.' A volume is defined as the volume the CO2 in
beer would occupy at 0° F and atmospheric pressure, relative to
the volume of the beer itself. For example, the CO2 in one pint
of British Ale carbonated to 2 volumes of CO2 would occupy two
pints of space.
For
reference, here is a list of beer styles and the corresponding
amount of [recommended] carbonation:
British Ale: 1.8 to 2.2 volumes
German Lager: 2.5 volumes
American Lagers and Ale: 2.6 to 2.8 volumes
Wheat Beers: 3.0 volumes
With the assistance of Table 1, it is possible
to precisely carbonate a beer to any arbitrary level of
carbonation... The top row contains the pressure in pounds per
square inch. The first column lists beer temperatures. The
numbers in the center represent the volumes of CO2 that will be
dissolved in the beer at equilibrium.
In order to duplicate the carbonation of a
German Lager, for example, you would need to force 2.5 volumes
of CO2 into the beer. If you know your refrigerator is set at
45° F, you can consult Table 1 to determine that 2.5 volumes of
CO2 is achieved at 15 PSI. If you were to lower the temperature
of the refrigerator to 35° F, you would need just 10 PSI of
pressure to achieve the same level of carbonation.
Table 1.
Carbonation Chart
|
Temperature |
5 PSI |
10 PSI |
15 PSI |
20 PSI |
25 PSI |
30 PSI |
|
30° F |
2.23 |
2.82 |
|
|
|
|
|
35° F |
2.02 |
2.52 |
3.02 |
|
|
|
|
40° F |
1.83 |
2.30 |
2.75 |
3.19 |
|
|
|
45° F |
1.66 |
2.08 |
2.51 |
2.94 |
|
|
|
50° F |
1.50 |
1.90 |
2.30 |
2.70 |
3.10 |
|
|
55° F |
|
1.75 |
2.12 |
2.47 |
2.83 |
3.18 |
|
60° F |
|
1.62 |
1.95 |
2.27 |
2.60 |
2.92 |
Simply
setting the regulator pressure to the proper level will cause
the beer to become carbonated. However, it may take many days
for the beer to reach equilibrium with this method... If the
beer becomes over-carbonated, it is possible to decarbonate the
beer. You should periodically pull the pressure relief valve on
the keg, de-pressurizing the head space. This will cause CO2 to
come out of solution and re-pressurize the head space, at which
point you can repeat the process. In extreme cases of
over-carbonation, or very full kegs, you may find it
advantageous to leave the keg open to the atmosphere by
attaching a gas disconnect to the 'IN' post."
