My brewing buddy and I went Nitro at the same time. He did as Int3lig3ntdzign did and the beer served out okay but doesnt have that classic 'Guiness' Nitro cascade of fine bubbles. Its a light cascade at best.
My procedure: I kegged the beer and hit it with 40 psi of the Nitro gas mix (25% CO2). No straight CO2 at all. I shaked the hell out of it and hit it with 40 psi again. I repeat that for a few days until no more pressure will go in. Bascially the CO2 gets saturated (equivalent of 10 psi CO2) and the Nitrogen gets absorbed a little...but not much.
Chilled it down and hooked it up to my line with a Nitro faucet and it pours beautifully! Looks just like a Guiness pour - although it only takes about eight seconds to fill a glass. The cascade of bubbles is something to behold! SO SO CREAMY! Its like drinking light, frothy, chocolate milk. I serve at 35 to 40 psi on the Nitro gas mix - perfect pour every time.
I found this on a Probrewer discussion site:
To hopefully add to the discussion, John Mallet in his New Brewer article from Nov/Dec 1997 article points out that ranges for commercial beers are from 10-35ppm with 20-25ppm being typical nitrogenated stout levels. He also points out that the equilibrium for beer at 5C(41F) and 15psig is 2.7vol for CO2 and just .004vols N2 (15psig is a lot less than 35psig and yes it is adsorbed). Hey I didn’t say it was a lot in solution but it is in solution!
It is important to remember that a nitrogenated beer is not just nitrogen but also CO2. Nitrogen solubility is so poor that it almost completely goes to gas phase in a near instantaneous manner when the equilibrium pressure is removed. For nitrogenated beer the trick is to get the CO2 out of solution at the same time. The problem is that the CO2 has little drive to leave solution due to its high solubility and typically moderate levels from 1.6-2.0vols in nitrogenated beer. So the solution is to push the beer through a plate that has pinholes that will create massive turbulence thus knocking the CO2 out even though it didn’t want to. The higher ~31psig delivery pressures are necessary to not only keep the small amount of nitrogen in solution (with “beer gas”) but also overcome the high restriction of the pin holes. So with both the nitrogen and CO2 coming out of solution you have nitrogen seeding CO2 bubbles. Since nucleation size is the most important factor in initial bubble size you start with tiny bubbles. And since nitrogen has a very small gas diffusion coefficient (especially compared to CO2) it maintains small bubbles (even with CO2 mixed in).http://discussions.probrewer.com/showthread.php?5039-Nitrogen-Fairy-Tales/page2