Fri Sep 24, 2010 4:06 am
When you set your regulator to 30 psig that means that the absolute pressure is 30 + 14.7 = 44.7 psia. If the gas is pure CO2 then the pressure of CO2 in the keg is 44.7 psia. But if the gas is a blend of 25% CO2 the "partial pressure" of CO2 is 0.25*44.7 or about 11.2 psia which is less than one atmosphere (an atmosphere is 14.7 psia). It is the CO2 partial pressure which determines the carbonation level of the beer. Obviously, it's going to be pretty low and a 25% mix is better called "stout gas" because stout is the only beer that you would want to serve with it. The idea here is to use the total pressure of the mix (the nitrogen does not dissolve in the beer to an appreciable extent) to force the low carbonated beer vigorously through small holes in the sparkler plate thus forcing it to give up what little dissolved CO2 it contains to form the classic creamy head. A well poured stout is pretty flat (but there should be enough dissolved gas left to give some "life" to the beer.)
"Beer gas" is usually around 60% CO2 which, with the 30 psig regulator setting will give you a partial pressure of CO2 of 26.8 psia which is equivalent to 26.8 - 14.7 = 12.1 psig. As far as carbonation is concerned the beer thinks it is under 12 psig pure CO2. As nitrogen is a lot less soluble than CO2 it is as if it isn't there in terms of carbonation. But it can push beer. So if you have a beer that should be, at its proper serving temperature, on 12 psi CO2 but you have to push it from the cellar to a bar way at the other end of the building, the friction in the long lines would slow the flow way below the 2 Oz/sec. rate considered desirable. Here's where beer gas comes into play. You can put 30 psig "serving pressure" on it while only having 12 psig "carbonation pressure" on it. It pours at 2 Oz/sec but is not overly carbonated.
So you would only be interested in the 25% mix if you are serving stout and a 60% mix if you have long lines. In the UK blends are commonly used with a sparkler on ales other than stouts with the object being to get the creamy head without having to use a beer engine.
The final consideration WRT blends is that they are gas. A bottle about the same size as a 5 pound CO2 bottle will only push 1 - 1/2 to 2 kegs (Sankey - not cornelius) of beer. A 5 pound CO2 bottle, conversely, holds 5 pounds of CO2 which should push a dozen or more.
