We are having problems with foaming in our nitro beer, we carbonate it to a low level and then use a blended gas to push it through the nitro tap.
The thing that makes nitro beers give that wonderful “break out” of tiny bubbles and produce the creamy, stable head of foam is that unlike CO2, nitrogen does not dissolve well into beer but once dissolved it likes to stay there, in fact the nitro tap system forces the beer under high pressure through an “agitator plate” containing small holes in order to rouse the nitrogen to start its foaming process. In the world of physics and gas laws substances try to come back into equilibrium with their atmospheric concentration and the atmosphere we are breathing right now is about 78% nitrogen, 21% oxygen and about 0.04% CO2. That means that once nitrogen has been dissolved into the beer under high pressure it wants to stay in solution and forms those tiny bubbles which have a high surface tension and are wonderfully stable at the top of the pint. Essentially a stable nitrogen beer is interrupted by large amounts of carbonation present, which unlike nitrogen, wants to come out of solution fairly readily (there being a much smaller concentration of CO2 in the atmosphere). CO2 present in large amounts in the beer under the high driving pressure of a nitro tap will yield foam. To produce nitrogenated beers you need to eliminate carbonation- CO2 is not your friend- that means: